ALBERT

Description: The InSight spacecraft was proposed to be a build-to-print copy of the Phoenix vehicle due to the knowledge that the lander payload would be similar and the trajectory would be similar. However, the InSight aerothermal analysts, based on tests performed in CO2 during the Mars Science Laboratory mission (MSL) and completion of Russian databases, considered radiative heat flux to the aftbody from the wake for the first time for a US Mars mission. The combined convective and radiative heat flux was used to determine if the as-flown Phoenix thermal protection system (TPS) design would be sufficient for InSight. All analyses showed that the design would be adequate. Once the InSight lander was successfully delivered to Mars on November 26, 2018, work began to reconstruct the atmosphere and trajectory in order to evaluate the aerothermal environments that were actually encountered by the spacecraft and to compare them to the design environments.The best estimated trajectory (BET) reconstructed for the InSight atmospheric entry fell between the two trajectories considered for the design, when looking at the velocity versus altitude values. The maximum heat rate design trajectory (MHR) flew at a higher velocity and the maximum heat load design trajectory (MHL) flew at a lower velocity than the BET. For TPS sizing, the MHL trajectory drove the design. Reconstruction has shown that the BET flew for a shorter time than either of the design environments, hence total heat load on the vehicle should have been less than used in design. Utilizing the BET, both DPLR and LAURA were first run to analyze the convective heating on the vehicle with no angle of attack. Both codes were run with axisymmetric, laminar flow in radiative equilibrium and vibrational non-equilibrium with a surface emissivity of 0.8. Eight species Mitcheltree chemistry was assumed with CO2, CO, N2, O2, NO, C, N, and O. Both codes agreed within 1% on the forebody and had the expected differences on the aftbody. The NEQAIR and HARA codes were used to analyze the radiative heating on the vehicle using full spherical ray-tracing. The codes agreed within 5% on most aftbody points of interest.The LAURA code was then used to evaluate the conditions at angle of attack at the peak heating and peak pressure times. Boundary layer properties were investigated to confirm that the flow over the forebody was laminar for the flight.Comparisons of the aerothermal heating determined for the reconstructed trajectory to the design trajectories showed that the as-flown conditions were less severe than design

Description: Improvements and results of a new method are presented that computes a pre-test estimate of the precision error of the drag coefficient of a wind tunnel model. The error estimate is defined as the part of the drag coefficient's precision error that is primarily associated with the precision error of the angle of attack measurement and physical characteristics of the chosen strain-gage balance. The method indirectly describes the precision error of the angle of attack measurement by using an assumed balance gage output variation of one microV/V. The physical characteristics of the balance, on the other hand, are described by partial derivatives of the axial and normal forces with respect to the strain-gage outputs. These derivatives can directly be obtained from the data reduction matrix of the balance. The precision error estimate itself is calculated by applying a simple explicit equation that uses the model reference area, the dynamic pressure, the angle of attack, the coefficients of the linear terms of the data reduction matrix, and the electrical output variation of one microvolt per volt as input. Precision errors at constant angle of attack may be visualized as contour plots by plotting them, for example, versus the Mach number and the total pressure. Characteristics of NASA's MC60E balance are used in combination with the reference area of a generic wind tunnel model in order to demonstrate that error estimates are independent of both the balance load format and the units chosen for the description of balance loads, model reference area, and the dynamic pressure. Finally, experimental data from a wind tunnel test of the Ames Check Standard Model in the NASA Ames 11-foot Transonic Wind Tunnel illustrates the application of the method to real-world test data.

Description: Wake vortex spacing standards constrict the terminal area throughput and impose severe constraints on the overall capacity and efficiency of the National Airspace System. For more than two decades starting in the early 1990s, the National Aeronautics and Space Administration conducted extensive research on characterizing the formation and evolution of aircraft wakes. This multidisciplinary work included comprehensive field experiments (Pruis et al. 2016), flight tests (Vicroy et al. 1998), and wind tunnel tests (Rossow 1994; Chow et al. 1997). Parametric studies using large eddy simulations (Proctor 1998; Proctor et al. 2006) were conducted in order to develop fast-time models for the prediction of wake transport and decay (Ahmad et al. 2016). Substantial effort was spent on the formulation of acceptable vortex hazard metrics (Tatnall 1995; Hinton and Tatnall 1997). Several wake encounter severity metrics have been suggested in the past, which include the wake circulation strength, vortex-induced rolling moment coefficient (Clv), bank angle, and the roll control ratio (Tatnall 1995; Hinton and Tatnall 1997; Van der Geest 2012). The vortex-induced rolling moment coefficient introduced by Bowles and Tatnall (Tatnall 1995; Gloudemans et al. 2016) has been used extensively for risk and safety analysis of newly proposed air traffic management concepts and procedures. The original method of Bowles and Tatnall assumed a constant wing loading (the wing lift-curve slope, CL is constant), which resulted in an overestimation of the vortexinduced rolling moment coefficient. Bowles (2014) suggested a correction to the original method that provides more accurate values of Clv and which is also consistent with the underlying physics of the problem. The overestimation of Clv in the original method can be corrected by assuming an elliptical lift distribution. Figure 1.1 illustrates the correction in Clv achieved by the modified method.

Description: National airspace, the management for access and operation of these vehicles is required. This management is being developed under the unmanned aircraft system traffic management system (UTM) program. To determine the aerodynamic characteristics of drones, wind tunnel experiments and computation fluid dynamic (CFD) analysis have been conducted. These experiments and analyses are undertaken to understand the flight capabilities of these vehicles in variable head and cross wind conditions. The results of these investigations will provide metrics for the safe operation of these vehicles in and around civil populations and in urban settings. The focus of this paper is to model a drone installed in a wind tunnel for varying pitch attitudes and rotor rpm settings. Specifically, the IRIS drone is modeled in the NASA-Ames 7x10 ft. W/T. The tunnel mounting hardware and the tunnel enclosure are modeled with the IRIS drone geometry. The rotors of the drone are modeled using two methodologies: a rotor disk model and individual blade representations. The results of the analysis are compared with available experimental data to validate the computational approach.

Description: The Mid-Lift-to-Drag ratio Rigid Vehicle (MRV) is a candidate in the NASA multi-center effort to determine the most cost effective vehicle to deliver a large-mass payload to the surface of Mars for a human mission. Products of this effort include six-degree-of-freedom (6DoF) entry-to-descent trajectory performance studies for each candidate vehicle. These high fidelity analyses help determine the best guidance and control (G&C) strategies for a feasible, robust trajectory. This paper presents an analysis of the MRV's G&C design by applying common entry and descent associated uncertainties using a Fully Numerical Predictor-corrector Entry Guidance (FNPEG) and tunable Apollo powered descent guidance.

Description: Artificial ice shapes of various geometric fidelity were tested on a wing model based on the Common Research Model. Low Reynolds number test were conducted at Wichita State University's Walter H. Beech Memorial Wind utilizing an 8.9% scale model, and high Reynolds number tests were conducted at ONERA's F1 wind tunnel utilizing a 13.3% scale model. Several identical geometrically-scaled ice shapes were tested at both facilities, and the results were compared at overlapping Reynolds and Mach numbers. This was to ensure that the results and trends observed at low Reynolds number could be applied and continued to high, near-flight Reynolds number. The data from Wichita State University and ONERA F1 agreed well at matched Reynolds and Mach numbers. The lift and pitching moment curves agreed very well for most configurations. This confirmed results from previous tests with other ice shapes that indicated the data from the low Reynolds number tests could be used to understand ice-swept-wing aerodynamics at high Reynolds number. This allows ice aerodynamics testing to be performed at low Reynolds number facilities with much lower operating costs and generate results that are applicable to flight Reynolds number.

Description: The intermediate wakes of thin flat plates with circular trailing edges (TEs) are investigated here with direct numerical simulations (DNSs). The separating boundary layers are turbulent in all cases. The near wake in two thin-plate cases (IN & NS), with a focus on the vortex shedding process, was explored in a recent article. Intermittent shedding was observed in Case IN. Case NS, with half the TE diameter of Case IN, was an essentially non-shedding case. A third case (ST) with a sharp trailing edge was also investigated and found to exhibit an intermittent wake instability. The objectives of the present study are twofold. The first is to determine if the wake instability found in Case ST exists in Cases IN and NS as well. The second is to provide the distributions of the turbulent normal intensities and shear stress in the wake and to understand these distributions via the budget terms in the corresponding transport equations. The results show that both Cases IN & NS exhibit a wake instability in the intermediate wake region, that is similar to that found earlier in Case ST. We note that in Case IN, the presence of an intermediate-wake instability results in the co-existence of two different types of instability within a single wake. The distributions of the turbulent normal intensities and shear stress, and the budget terms for the streamwise intensity are included and discussed here. All the budget terms contribute appreciably to the overall budget in the transport equation for streamwise normal intensity.

Description: US Army MC-4/5 ram-air parachutes were tested in the 80- by 120-Ft test section of the National Full-Scale Aerodynamics Complex. Arrays of targets on the upper and lower surfaces of the central cell of the canopies were measured by stereo photogrammetry, and the target positions were used to estimate both the shape of the cell and angle of attack of the canopy. Forces and moments were measured by a six-axis load cell. Based on the photogrammetry and load-cell measurements, the relationships between lift, drag, and angle of attack were determined over a range of trailing-edge flap deflections, front riser lengths, and free-stream airspeeds. This paper describes the test, with an emphasis on the photogrammetry measurements, and presents a summary of results.

Description: The Advanced Supersonic Parachute Inflation Research Experiments (ASPIRE) project waslaunched to develop the capability for testing supersonic parachutes at Mars-relevant conditions.Three initial parachute tests, targeted as a risk-reduction activity for NASA's upcomingMars2020 mission, successfully tested two candidate parachute designs and provided valuabledata on parachute inflation, forces, and aerodynamic behavior. Design of the flight tests dependedon flight mechanics simulations which in turn required aerodynamic models for the payload, andthe parachute. Computational Fluid Dynamics (CFD) was used to generate these models preflightand are compared against the flight data after the tests. For the payload, the reconstructedaerodynamic behavior is close to the pre-flight predictions, but the uncertainties in thereconstructed data are high due to the low dynamic pressures and accelerations during the flightperiod of comparison. For the parachute, the predicted time to inflation agrees well with the preflightmodel; the peak aerodynamic force and the steady state drag on the parachute are withinthe bounds of the pre-flight models, even as the models over-predict the parachute drag atsupersonic Mach numbers. Notably, the flight data does not show the transonic drag decreasepredicted by the pre-flight model. The ASPIRE flight tests provide previously unavailablevaluable data on the performance of a large full-scale parachute behind a slender leading bodyat Mars-relevant Mach number, dynamic pressure and parachute loads. This data is used topropose a new model for the parachute drag behind slender bodies to aid future experiments.

Description: Objectives: Reliable evaluation of mass flow rates through permeable boundaries - Estimate and control discretization error- Consider both computational domain outflow and inflow- Applicable to simulating propulsion-system effects, as well as secondary flow paths - Explore feasibility of handling more general outputs at domain boundaries. Design optimization subject to mass-flow-rate constraints - Improve aerodynamic performance and reduce noise due to sonic boom - Control discretization error in design space to improve confidence in final designs.

Description: The experimental, fully electric X-57 Maxwell is designed to enable lower energy con-sumption at cruise compare to a fuel burning baseline. This is to be achieved using a sumof subsystem benefits incorporated in the electric, airframe, and propulsion systems. AMission Planning Tool captures the three stages of X-57 development in order to assess thedesign of each subsystem in the context of the whole aircraft. The Mission Planning Toolfor the fully electric X-57 Maxwell captures the aerodynamics, propulsion, heat transfer,and power system of the aircraft with trajectory optimization capabilities. It is able tomodel these subsystems through all phases of flight, from taxi to landing. Through thismultidisciplinary approach, we are able to predict the benefit of each subsystem and theeffect of key design assumptions and how the aircraft will react if they are not met or ex-ceeded. As the aircraft progresses and systems are tested, we can use the Mission PlanningTool to continue to predict performance. This paper details the continued development ofthe X-57 Mission Planning Tool and demonstrates its capabilities.

Description: NASAs Advanced Air Transport Technology (AATT) project is investigating boundary layer ingesting (BLI) propulsors for advanced subsonic commercial vehicle concepts to enable the reduction of fuel burn. A multidisciplinary team of researchers from NASA, United Technologies Research Center (UTRC), Virginia Polytechnic University, and the Air Force Arnold Engineering Development Complex developed and tested an embedded BLI inlet and distortion-tolerant fan (BLI2DTF) system in the NASA Glenn Research Center (GRC) 8- foot by 6-foot (8x6) transonic wind tunnel. The test demonstrated the component performance goals necessary for an overall fuel burn reduction of 3 to 5 percent on a large hybrid wing body (HWB) aircraft. Special test equipment, including a raised floor with flow effectors and a bleed system, was developed for use in the 8x6 to produce the appropriate incoming boundary layer representative of an HWB application. Detailed measurements were made to determine the inlet total pressure loss and distortion, fan stage efficiency, and aeromechanic performance including blade vibration stress and displacement response. Results from this test were used as input to a vehicle-level system study performed by the AATT project to assess the impact of BLI on an alternative advanced concept aircraft referred to as the NASA D8 (ND8), which is somewhat similar to the HWB in its integration of the propulsor. This paper will provide an overview of the project timeline, special test equipment needed in the wind tunnel to develop the appropriate incoming boundary layer, and the difficulties in designing a propulsor for the test. The paper will conclude with some representative aerodynamic and aeromechanic data from the test itself and conclude with how this data was used in the ND8 system study.

Description: This manual describes the installation and execution of FUN3D version 13.6, including optional dependent packages. FUN3D is a suite of computational fluid dynamics simulation and design tools that uses mixed-element unstructured grids in a large number of formats, including structured multiblock and overset grid systems. A discretely-exact adjoint solver enables efficient gradient-based design and grid adaptation to reduce estimated discretization error. FUN3D is available with and without a reacting, real-gas capability. This generic gas option is available only for those persons that qualify for its beta release status.

Description: _NASA's Advanced Air Transport Technology (AATT) project is investigating boundary layer ingesting (BLI) propulsors for advanced subsonic commercial vehicle concepts to enable the reduction of fuel burn. A multidisciplinary team of researchers from NASA, United Technologies Research Center (UTRC), Virginia Polytechnic University, and the Air Force Arnold Engineering Development Complex developed and tested an embedded BLI inlet and distortion-tolerant fan (BLI2DTF) system in the NASA Glenn Research Center (GRC) 8-foot by 6-foot (8x6) transonic wind tunnel. The test demonstrated the component performance goals necessary for an overall fuel burn reduction of 3 to 5 percent on a large hybrid wing body (HWB) aircraft. Special test equipment, including a raised floor with flow effectors and a bleed system, was developed for use in the 8x6 to produce the appropriate incoming boundary layer representative of an HWB application. Detailed measurements were made to determine the inlet total pressure loss and distortion, fan stage efficiency, and aeromechanic performance including blade vibration stress and displacement response. Results from this test were used as input to a vehicle-level system study performed by the AATT project to assess the impact of BLI on an alternative advanced concept aircraft referred to as the NASA D8 (ND8), which is somewhat similar to the HWB in its integration of the propulsor. This paper will provide an overview of the project timeline, special test equipment needed in the wind tunnel to develop the appropriate incoming boundary layer, and the difficulties in designing a propulsor for the test. The paper will conclude with some representative aerodynamic and aeromechanic data from the test itself and conclude with how this data was used in the ND8 system study.

Description: Thermal Protection System (TPS) modeling requires accurate representation and prediction of the thermomechanical behavior of ablative materials. State-of-the-art TPS materials such as Phenolic Impregnated Carbon Ablator (PICA) have a proven flight record and demonstrate exceptional capabilities for handling extreme aerothermal heating conditions. The constant push for lightweight materials that are flexible in their design and performance, and hence allow for a wide range of mission profiles, has led NASA over the past years to develop its Heatshield for Extreme Entry Environment Technology (HEEET). HEEET is based primarily on a dual layer woven carbon fiber architecture and the technology has successfully been tested in arc-jet facilities. These recent developments have sparked interest in the accurate micro-scale modeling of composite weave architectures, to predict the structural response of macro-scale heatshields upon atmospheric entry. This effort can be extended to incorporate in-depth failure mechanics analyses as a result of local thermal gradients or high-velocity particle impact.

Description: Prediction and control of the onset of transition and the associated variation in aerothermodynamic parameters in high-speed flows is key to optimize the performance and design of Thermal Protection Systems (TPS) of next-generation aerospace vehicles [1]. Boundary Layer Transition (BLT) characteristics can influence the surface heating budget determining the TPS thickness and consequently its weight penalty. Ablative heatshields are designed to alleviate the high heat flux at the surface through pyrolysis of their polymeric matrix and subsequent fiber ablation [2]. Pyrolysis leads to out-gassing and non-uniform ablation lead to surface roughness, both of which are known to influence the transition process. An ablator impacts BLT through three main routes: gas injecting into the boundary layer from the wall, changing the surface heat transfer due to wall-flow chemical reactions, and modifying surface roughness [3]. In preparation to Mars 2020 mission post-flight analysis, the predictive transition capability has been initiated toward hard-coupling porous material response analysis and aerothermal environment calculation.

Description: The Mars Science Laboratory (MSL) Entry, Descent and Landing Instrumentation (MEDLI) collected in-flight data largely used by the ablation community to verify and validate physics-based models for the response of the Phenolic Impregnated Carbon Ablator (PICA) material [1-4]. MEDLI data were recently used to guide the development of NASAs high-fidelity material response models for PICA, implemented in the Porous material Analysis Toolbox based on OpenFOAM (PATO) software [5-6]. A follow-up instrumentation suite, MEDLI2, is planned for the upcoming Mars 2020 mission [7] after the large scientific impact of MEDLI. Recent analyses performed as part of MEDLI2 development draw the attention to significant effects of a protective coating to the aerothermal response of PICA. NuSil, a silicone-based overcoat sprayed onto the MSL heatshield as contamination control, is currently neglected in PICA ablation models. To mitigate the spread of phenolic dust from PICA, NuSil was applied to the entire MSL heatshield, including the MEDLI plugs. NuSil is a space grade designation of the siloxane copolymer, primarily used to protect against atomic oxygen erosion in the Low Earth Orbit environment. Ground testing of PICA-NuSil (PICA-N) models all exhibited surface temperature jumps of the order of 200 K due to oxide scale formation and subsequent NuSil burn-off. It is therefore critical to include a model for the aerothermal response of the coating in ongoing code development and validation efforts.

Description: NASA is investigating the potential of integrating acoustic liners into fan cases to reduce fan noise, while maintaining the fans aerodynamic performance. An experiment was conducted to quantify the aerodynamic impact of circumferentially grooved fan cases with integrated acoustic liners on a 1.5 pressure ratio turbofan rotor. In order to improve the ability to measure small performance changes, fan performance calculations were updated to include real gas effects including the effect of humidity. For all fan cases tested, the measured difference in fan isentropic efficiency was found to be less than the measurement repeatability for a torque-based efficiency calculation (approx. = 0.2%), however, an unintended tip clearance difference between configurations makes it difficult to determine if circumferentially grooved fan cases degraded fan performance. Fan exit turbulence measurements showed a 1.5% reduction in total turbulence intensity between hardwall and circumferentially grooved fan cases in the tip vortex region, which is attributed to a disruption in the formation of the tip leakage vortex. This decrease in fan exit turbulence could potentially lead to a 1-2dB reduction in broadband rotor-stator interaction noise. Reduced aerodynamic performance losses associated with over-the-rotor liners could enable further fan noise reduction.

Description: A full-scale isolated proprotor test is currently being conducted in the USAF National Full-Scale Aerodynamics Complex (NFAC) 40- by 80-Foot Wind Tunnel at NASA Ames. The test article is a 3-bladed research rotor derived from the right-hand rotor of the AW609; this rotor was manufactured by Bell Helicopter under contract to NASA. In this paper, this research rotor is referred to as "699". The test, nearly completed, is an integral part of the initial checkout test of the newly developed Tiltrotor Test Rig (TTR), whose purpose is to test advanced, full-scale proprotors in the NFAC. Figure 1 shows the TTR/699 installed in the 40- by 80-Foot test section. The TTR rotor axis is horizontal and the rig rotates in yaw on the wind tunnel turntable for conversion (transition) and helicopter mode testing. To date, a substantial amount of wind tunnel test data has already been acquired. The completed operational conditions include hover, airplane mode (cruise, wind tunnel airspeed V=61 to 267 knots), and the helicopter and conversion conditions (with a comprehensive sweep of the TTR yaw angle ranging, to date, from 90-deg yaw helicopter mode to 30-deg yaw conversion mode, at varying airspeeds). This 699 proprotor performance and loads correlation study uses these newly acquired wind tunnel test data. This paper represents the third analytical study, coming after two earlier analytical studies on the TTR/699; that is, a 2018 paper on pre-test predictions of 699 performance and loads, Ref. 1, and an upcoming January 2019 paper on aeroelastic stability analysis of the TTR/699 installed in the 40- by 80-Foot Wind Tunnel, Ref. 2. Reference 8 will present an overview of the entire TTR/699 test program. For completeness, Ref. 3 addresses the development and initial testing of the TTR. Background information on the TTR effort at NASA Ames can be found at the Aeromechanics website: https://rotorcraft.arc.nasa.gov/Research/Facilities/ttr.html. To the authors' knowledge, the full-scale results presented in this paper are the first of their kind. A literature survey brought up several existing correlation studies, but these were either based on small-scale test data (for example, the studies performed by the University of Maryland) or full-scale aircraft flight test data (for example, flight tests conducted by Bell Helicopter). Separately, the 2009 NASA study involving the JVX rotor is relevant (see Ref.4). The JVX is closely similar to the 699 in size and aerodynamics, and is accordingly a good reference for performance calculations. In Ref. 1 (as mentioned above), pre-test reality checks of the current analytical model were made by comparing JVX and 699 predictions in hover and forward flight (airplane mode).

Description: Two full seven-equation turbulence models have been implemented into the FUN3D code to evaluate their ability to improve the computation of challenging flows encountered in aerospace propulsion, including mixing flows. These models are the SSG/LRR and Wilcox full second-moment Reynolds stress models. They solve equations for the six components of the Reynolds stress and a seventh equation for the mixing length. Two standard eddy viscosity models are also evaluated for comparison, the Spalart-Allmaras (SA) one-equation model and the Menter Shear Stress Transport (SST-V) two-equation turbulence model. Flow through an axisymmetric reference nozzle is examined at three flow conditions: subsonic unheated, subsonic heated, and near sonic unheated. Centerline profiles of velocity and turbulent kinetic energy and radial profiles of velocity, turbulent kinetic energy and turbulent stresses are examined. characteristics, no significant changes in the downstream flow behavior compared to the baseline case are observed. Furthermore, the total power consumed by the fans for different incoming flow conditions also remain marginally the same. It is hoped that the results, albeit obtained at very low speeds. would serve as a database for this technologically interesting flow field that has not been explored adequately before.

Description: Heated ethane (C2H6) has been proposed as an alternative to inert gases for use as a motive fluid in the experimental simulation of rocket exhaust plumes. By adjusting stagnation temperature, the isentropic exponent of ethane can be tuned to approximate those produced by common rocket propellants including hydrogen, hypergols, alcohols, and hydrocarbons. As a result, ethane can be made to follow a nozzle expansion process which is nearly identical to realistic rocket engine flow fields. Additionally, its high auto-ignition temperature and resistance to condensation enable the testing of expansion ratios much larger than conventional inertgas testing. NASA SSC has performed quasi-one-dimensional analyses using the Chemical Equilibrium with Applications (CEA) code as a preliminary means to compare flow fields produced by non-reacting ethane to those of reacting combustion products. A LO2/LH2 rocket engine operating at a chamber pressure of 5.0 MPa and a mixture ratio of 6.1 was used as an example case to demonstrate ethanes efficacy as a simulant. Errors for key similarity parameters were compared to legacy cold-flow test methods. Additional errors induced by machining tolerances and chemical impurities were also examined. Results suggest that at a 3% geometric scale and ~500 K ethane stagnation temperature, an error of less than 2.5% throughout the flow field is realistically achievable along the dimensions of Mach number, Reynolds number, pressure ratio, and isentropic exponent. The development of an experimental test bed for validation of this configuration is currently underway.

Description: A 13.49-percent-thick, slotted, natural-laminar-flow airfoil, the S207, for a transport aircraft has been designed and analyzed theoretically. The two primary objectives of high maximum lift, insensitive to roughness, and low profile drag have been achieved. The drag-divergence Mach number is predicted to be greater than 0.70.

Description: NASA's ASPIRE (Advanced Supersonic Parachute Inflation Research Experiments) project was launched to investigate the supersonic deployment, inflation and aerodynamics of full-scale disk-gap-band (DGB) parachutes. Three flight tests (October 2017, March 2018 and July 2018) deployed and examined parachutes meant for the upcoming "Mars 2020" mission. Mars-relevant conditions were achieved by performing the tests at high altitudes over Earth on a sounding rocket platform, with the parachute deploying behind a slender body (roughly 1/6-th the diameter of the capsule that will use this parachute for descent at Mars). All three tests were successful and delivered valuable data and imagery on parachute deployment and performance. CFD simulations were used in designing the flight test, interpreting the flight data, and extrapolating the results obtained during the flight test to predict parachute behavior at Mars behind a blunt capsule. This presentation will provide a brief overview of the test program and flight test data, with emphasis on differences in parachute performance due to the leading body geometry.

Description: Aerodynamic assessment of icing effects on swept wings is an important component of a larger effort to improve three-dimensional icing simulation capabilities. An understanding of ice-shape geometric fidelity and Reynolds and Mach number effects on iced-wing aerodynamics is needed to guide the development and validation of ice-accretion simulation tools. To this end, wind-tunnel testing was carried out for 8.9% and 13.3% scale semispan wing models based upon the Common Research Model airplane configuration. Various levels of geometric fidelity of an artificial ice shape representing a realistic glaze-ice accretion on a swept wing were investigated. The highest fidelity artificial ice shape reproduced all of the three-dimensional features associated with the glaze ice accretion. The lowest fidelity artificial ice shapes were simple, spanwise-varying horn ice geometries intended to represent the maximum ice thickness on the wing upper surface. The results presented in this paper show that changes in Reynolds and Mach number have only a small effect on the iced-wing aerodynamics relative to the clean-wing configuration. Furthermore, the addition of grit roughness to some lower-fidelity artificial ice shapes resulted in favorable lift and pitching moment comparisons to the wing with the highest fidelity artificial ice shape. For the wing with simple horn ice shapes, the dependence of maximum lift coefficient on horn height and angle are generally consistent with the trends observed for similar experiments conducted on iced airfoils in past research. In terms of usable lift however, the horn height did have a significant effect even for lower horn angles. This could be an important finding since usable lift may be more indicative of the impending iced-swept wing stall and need for additional pitch control than maximum lift coefficient.

Description: Swept wings and control surfaces are common elements of modern aircraft, and it has been shown both experimentally and theoretically that laminar-to-turbulent transition of the three-dimensional boundary layer that develops over them is highly sensitive to surface roughness. Numerous studies have been conducted on the effect of discrete roughness elements or distributed roughness elements on swept flow transition, however so far limited computational effort has been dedicated to the study of transition over swept wings with randomly distributed micron-sized roughness. In the present work, we set up to reproduce the extensive experimental data base generated by Dagenhart et al for the infinite swept wing NLF(2)-0415. To this purpose, we perform scale-resolving simulations of flow transition over smooth and rough surfaces using a high-order space-time spectral-element Discontinuous-Galerkin solver. Different types of surface roughnesses are implemented by elastically deforming the original mesh. The study shows that the experimental results cannot be accounted for by a perfectly smooth wing and reveals a strong sensitivity of the transition process to the representation of the surface roughness. The crossflow patterns and transition location approach those measured for some of the surface profiles, however a correlation between the wavenumber spectrum of the surface, grid resolution and boundary layer stability is yet to be established.

Description: Author(s): Pavel A. Volkov and Sergej Moroz We consider the stability of nodal surfaces in fermionic band systems with respect to the Coulomb repulsion. It is shown that nodal surfaces at the Fermi level are gapped out at low temperatures due to emergent particle-hole orders. Energy dispersion of the nodal surface suppresses the instability t... [Phys. Rev. B 98, 241107(R)] Published Thu Dec 13, 2018

Description: Author(s): Xiancong Lu and D. Sénéchal We investigate parity-mixing superconductivity in the two-dimensional Hubbard model with Rashba spin-orbit coupling, using cellular dynamical mean-field theory (CDMFT). A superconducting state with mixed singlet d -wave and triplet p -wave character is found in a wide range of doping. The singlet comp... [Phys. Rev. B 98, 245118] Published Thu Dec 13, 2018

Description: Author(s): Alireza Habibi, S. A. Jafari, and S. Rouhani We elucidate the reduction of the winding number caused by the on-site disorder in a next-nearest-neighbor XY model. When disorder becomes strong enough, Majorana edge modes become critically extended, beyond which they collapse into Anderson localized (AL) states in the bulk, resulting in a topolog... [Phys. Rev. B 98, 035142] Published Thu Jul 26, 2018

Description: Author(s): Carsten A. Ullrich To describe noncollinear magnetism in systems such as spiral ferromagnets or spin-frustrated molecules, density-functional methods need to give a proper account of the interplay between broken spin symmetries and exchange-correlation many-body effects. Here, the author develops a class of orbital-dependent exchange-correlation functionals for systems with noncollinear spin, treating correlation via a self-consistent scheme inspired by the Singwi-Tosi-Land-Sjölander method. The approach is applied to a very simple yet nontrivial benchmark system, the asymmetric half-filled Hubbard dimer, and is found to perform well, particularly in the weakly to moderately correlated regime. [Phys. Rev. B 98, 035140] Published Thu Jul 26, 2018

Description: Author(s): Kai Luo, Valentin V. Karasiev, and S. B. Trickey A simple, unconventional, nonempirical, constraint-based orbital-free generalized gradient approximation (GGA) noninteracting kinetic energy density functional is presented along with illustrative applications. The innovation is adaptation of constraint-based construction to the essential properties... [Phys. Rev. B 98, 041111(R)] Published Thu Jul 26, 2018

Description: Author(s): Dino Novko The unusual Raman spectrum of MgB 2 and its formidable temperature dependence are successfully reproduced by means of a parameter-free ab initio nonadiabatic theory that accounts for the electron-hole pair scattering mechanisms with the system phonons. This example turns out to be a prototypical case... [Phys. Rev. B 98, 041112(R)] Published Thu Jul 26, 2018

Description: Author(s): W. H. Brito, S. Choi, Y. X. Yao, and G. Kotliar We investigate the normal state of the superconducting compound PuCoGa 5 using the combination of density functional theory (DFT) and dynamical mean-field theory (DMFT), with the continuous time quantum Monte Carlo (CTQMC) and the vertex-corrected one-crossing approximation (OCA) as the impurity solv... [Phys. Rev. B 98, 035143] Published Fri Jul 27, 2018

Description: Author(s): Yi-Yan Wang (王义炎), Lin-Lin Sun (孙琳琳), Sheng Xu (徐升), Yuan Su (苏园), and Tian-Long Xia (夏天龙) We report the magnetotransport properties of HoSb, a semimetal with antiferromagnetic ground state. HoSb shows extremely large magnetoresistance (XMR) and Shubnikov-de Haas (SdH) oscillation at low temperature and high magnetic field. Different from previous reports in other rare earth monopnictides... [Phys. Rev. B 98, 045137] Published Fri Jul 27, 2018

Description: Author(s): Irakli Titvinidze, Max E. Sorantin, Antonius Dorda, Wolfgang von der Linden, and Enrico Arrigoni We address the steady-state behavior of a system consisting of several correlated monoatomic layers sandwiched between two metallic leads under the influence of a bias voltage. In particular, we investigate the interplay of the local Hubbard and the long-range Coulomb interaction on the charge redis... [Phys. Rev. B 98, 035146] Published Fri Jul 27, 2018

Description: Author(s): Akitoshi Nakano, Takumi Hasegawa, Shinya Tamura, Naoyuki Katayama, Satoshi Tsutsui, and Hiroshi Sawa Ta 2 NiSe 5 is considered a promising excitonic insulator (EI) candidate, in which the EI state is due to Coulomb interaction between electrons and holes. In Ta 2 NiSe 5 , the role of phonons is significant since the EI transition is accompanied by an orthorhombic-to-monoclinic structural transition at T s = ... [Phys. Rev. B 98, 045139] Published Mon Jul 30, 2018

Description: Author(s): F. C. Chen, X. Luo, J. Yan, Y. Sun, H. Y. Lv, W. J. Lu, C. Y. Xi, P. Tong, Z. G. Sheng, X. B. Zhu, W. H. Song, and Y. P. Sun Topological Weyl semimetals (WSMs), a new quantum state of matter, provide the realization of relativistic Weyl fermions in solid-state physics. The appearance of the Weyl nodes will demonstrate novel transport phenomena related to the chiral anomaly. Theoretical prediction hints that the giant plan... [Phys. Rev. B 98, 041114(R)] Published Mon Jul 30, 2018

Description: Author(s): M. Naseska, A. Pogrebna, G. Cao, Z. A. Xu, D. Mihailovic, and T. Mertelj We report on a systematic excitation-density-dependent all-optical femtosecond time-resolved study of the spin density wave state in iron-based superconductors. The destruction and recovery dynamics are measured by means of the standard and a multipulse pump-probe technique. The experimental data ar... [Phys. Rev. B 98, 035148] Published Mon Jul 30, 2018

Description: Author(s): Rui-Qi Xing, Laura Classen, and Andrey V. Chubukov We study the structure of the orbital order Γ = d x z † d x z − d y z † d y z in FeSe in light of recent scanning tunneling microscopy and angle-resolved photoemission spectroscopy (ARPES) data, which detect the shapes of the hole and electron pockets in the nematic phase. The geometry of the pockets indicates that... [Phys. Rev. B 98, 041108(R)] Published Tue Jul 24, 2018

Description: Author(s): A. Amaricci, A. Valli, G. Sangiovanni, B. Trauzettel, and M. Capone We investigate the emergence of antiferromagnetic ordering and its effect on the helical edge states in a quantum spin Hall insulator, in the presence of strong Coulomb interaction. Using dynamical mean-field theory, we show that the breakdown of lattice translational symmetry favors the formation o... [Phys. Rev. B 98, 045133] Published Tue Jul 24, 2018

Description: Author(s): Peng-Jie Guo, Huan-Cheng Yang, Kai Liu, and Zhong-Yi Lu As a type of fermions without counterpart in high energy physics, triply degenerate fermions show exotic physical properties, which are represented by triply degenerate nodal points in topological semimetals. Here, based on the space group theory analysis, we propose a practical guidance for seeking... [Phys. Rev. B 98, 045134] Published Tue Jul 24, 2018

Description: Author(s): Shiang Fang, Stephen Carr, Miguel A. Cazalilla, and Efthimios Kaxiras We derive electronic tight-binding Hamiltonians for strained graphene, hexagonal boron nitride, and transition-metal dichalcogenides based on Wannier transformation of ab initio density functional theory calculations. Our microscopic models include strain effects to leading order that respect the he... [Phys. Rev. B 98, 075106] Published Mon Aug 06, 2018

Description: Author(s): Vojtěch Vlček, Wenfei Li, Roi Baer, Eran Rabani, and Daniel Neuhauser We introduce the concept of sparse stochastic compression, an efficient stochastic sampling of any general function. The technique uses sparse stochastic orbitals (SSOs), short vectors that sample a small number of space points. As a first demonstration, SSOs are applied in conjunction with simple d... [Phys. Rev. B 98, 075107] Published Mon Aug 06, 2018

Description: Author(s): Daniel Kidd, A. S. Umar, and Kálmán Varga An iterative optimization approach that simultaneously minimizes the energy and optimizes the Lagrange multipliers enforcing desired constraints is presented. The method is tested on previously established benchmark systems and it is proved to be efficient and accurate. The approach can also be effi... [Phys. Rev. B 98, 075108] Published Mon Aug 06, 2018

Description: Author(s): Alex Thomson, Shubhayu Chatterjee, Subir Sachdev, and Mathias S. Scheurer We present the electronic band structures of states with the same symmetry as the three-sublattice planar antiferromagnetic order of the triangular lattice. Such states can also be defined on the honeycomb lattice provided the spin density waves lie on the bonds. We identify cases which are consiste... [Phys. Rev. B 98, 075109] Published Mon Aug 06, 2018

Description: Author(s): Andrzej Biborski, Andrzej P. Kądzielawa, and Józef Spałek We discuss electronic properties and their evolution for the linear chain of H 2 molecules in the presence of a uniform external force f acting along the chain. The system is described by an extended Hubbard model within a fully microscopic approach . Explicitly, the microscopic parameters describing ... [Phys. Rev. B 98, 085112] Published Tue Aug 07, 2018

Description: Author(s): Scott McKechnie, Jarvist M. Frost, Dimitar Pashov, Pooya Azarhoosh, Aron Walsh, and Mark van Schilfgaarde Metal halide perovskites exhibit a materials physics that is distinct from traditional semiconductors. While materials such as CH 3 NH 3 PbI 3 are nonmagnetic, the presence of heavy elements (Pb and I) in a noncentrosymmetric crystal environment result in a spin splitting of the frontier electronic bands... [Phys. Rev. B 98, 085108] Published Mon Aug 06, 2018

Description: Author(s): Klaus Halterman, Mohammad Alidoust, and Alexander Zyuzin We theoretically study the electromagnetic response of type-I and type-II centrosymmetric Weyl metals. We derive an anisotropic permittivity tensor with off-diagonal elements to describe such gyrotropic media. Our findings reveal that for appropriate Weyl cones tilts, the real part of the transverse... [Phys. Rev. B 98, 085109] Published Mon Aug 06, 2018

Description: Author(s): Ke Yang, D. I. Khomskii, and Hua Wu While double perovskites A 2 B B ′ O 6 , if ordered, usually form a rock-salt–type structure with a checkerboard B − B ′ ordering, it is surprising that Ca 2 FeMnO 6 has alternate FeO 2 and MnO 2 layers in its perovskite structure. Here, by using density functional calculations, we demonstrate that this unusual la... [Phys. Rev. B 98, 085105] Published Mon Aug 06, 2018

Description: Author(s): SangEun Han and Eun-Gook Moon Topological states may be protected by a lattice symmetry in a class of topological semimetals. In three spatial dimensions, the Berry flux around gapless excitations in momentum space concretely defines a chirality, so a protecting symmetry may be referred to as a chiral symmetry. Prime examples in... [Phys. Rev. B 97, 241101(R)] Published Mon Jun 04, 2018

Description: Author(s): Duk Y. Kim, Shi-Zeng Lin, Franziska Weickert, P. F. S. Rosa, Eric D. Bauer, Filip Ronning, J. D. Thompson, and Roman Movshovich The thermal conductivity of heavy-fermion superconductor Ce 0.95 Nd 0.05 CoIn 5 was measured with a magnetic field rotating in the tetragonal a − b plane. The thermal conductivity exhibits a step within the high-field low-temperature (HFLT) phase, which exists above 8 Tesla within the superconducting state... [Phys. Rev. B 97, 245120] Published Wed Jun 13, 2018

Description: Author(s): Julián Rincón, Elbio Dagotto, and Adrian E. Feiguin We study the photoinduced breakdown of a two-orbital Mott insulator and resulting metallic state. Using time-dependent density matrix renormalization group, we scrutinize the real-time dynamics of the half-filled two-orbital Hubbard model interacting with a resonant radiation field pulse. The breakd... [Phys. Rev. B 97, 235104] Published Tue Jun 05, 2018

Description: Author(s): Yongping Du, Er-jun Kan, Hu Xu, Sergey Y. Savrasov, and Xiangang Wan A search for new topological quantum systems is challenging due to the requirement of nontrivial band connectivity that leads to protected surface states of electrons. Progress in this field was primarily due to a realization of a band inversion mechanism between even and odd parity states that was ... [Phys. Rev. B 97, 245104] Published Tue Jun 05, 2018

Description: Author(s): Zheng Zhu, Itamar Kimchi, D. N. Sheng, and Liang Fu We investigate the non-Abelian topological chiral spin-liquid phase in the two-dimensional Kitaev honeycomb model subject to a magnetic field. By combining density matrix renormalization group and exact diagonalization we study the energy spectra, entanglement, topological degeneracy, and expectatio... [Phys. Rev. B 97, 241110(R)] Published Fri Jun 15, 2018

Description: Author(s): Chunxiao Liu, Xiao Chen, and Leon Balents The Sachdev-Ye-Kitaev (SYK) model is a quantum-mechanical model of fermions interacting with q -body random couplings. For q = 2 , it describes free particles and is nonchaotic in the many-body sense, while for q 〉 2 it is strongly interacting and exhibits many-body chaos. In this work we study the ent... [Phys. Rev. B 97, 245126] Published Fri Jun 15, 2018

Description: Author(s): Takami Tohyama, Michiyasu Mori, and Shigetoshi Sota The ground state of the t − t ′ − J ladder with four legs favors a striped charge distribution for the parameters corresponding to hole-doped cuprate superconductors. We investigate the dynamical spin and charge structure factors of the model by using the dynamical density matrix renormalization group (D... [Phys. Rev. B 97, 235137] Published Thu Jun 21, 2018

Description: Author(s): Agnese Tagliavini, Stefan Hummel, Nils Wentzell, Sabine Andergassen, Alessandro Toschi, and Georg Rohringer We present here two alternative schemes designed to correct the high-frequency truncation errors in the numerical treatment of the Bethe-Salpeter equations. The schemes are applicable to all Bethe-Salpeter calculations with a local two-particle irreducible vertex, which is relevant, e.g., for the dy... [Phys. Rev. B 97, 235140] Published Fri Jun 22, 2018

Description: Author(s): Adam Smith, Johannes Knolle, Roderich Moessner, and Dmitry L. Kovrizhin We study quantum quenches in two-dimensional lattice gauge theories with fermions coupled to dynamical Z 2 gauge fields. Through the identification of an extensive set of conserved quantities, we propose a generic mechanism of charge localization in the absence of quenched disorder both in the Hamilt... [Phys. Rev. B 97, 245137] Published Fri Jun 22, 2018

Description: Author(s): Juan Rubio-Zuazo, Ashish Chainani, Munetaka Taguchi, Daniel Malterre, Aida Serrano, and German R. Castro We study the electronic structure of well-characterized epitaxial films of FeO (wustite), γ − Fe 2 O 3 (maghemite), and Fe 3 O 4 (magnetite) using hard x-ray photoelectron spectroscopy (HAXPES), x-ray absorption near-edge spectroscopy (XANES), and electron energy loss spectroscopy (EELS). We carry out HAXPE... [Phys. Rev. B 97, 235148] Published Wed Jun 27, 2018

Description: Author(s): N. Pouse, S. Jang, B. D. White, S. Ran, R. B. Adhikari, C. C. Almasan, and M. B. Maple We report electrical resistivity, magnetization, and specific heat measurements on the correlated electron system Ce 1 − x Sm x CoIn 5 ( 0 ≤ x ≤ 1 ). Superconductivity (SC) in the heavy-fermion compound CeCoIn 5 , which is suppressed with increasing Sm concentration x , and antiferromagnetic (AFM) order of SmCoIn 5 ,... [Phys. Rev. B 97, 235149] Published Thu Jun 28, 2018

Description: Author(s): J. P. L. Faye, M. N. Kiselev, P. Ram, B. Kumar, and D. Sénéchal The interplay between the Kondo effect and magnetic ordering driven by the Ruderman-Kittel-Kasuya-Yosida interaction is studied within the two-dimensional Hubbard-Kondo lattice model. In addition to the antiferromagnetic exchange interaction J ⊥ between the localized spins and the conduction electron... [Phys. Rev. B 97, 235151] Published Thu Jun 28, 2018

Description: Author(s): Hennadii Yerzhakov and Joseph Maciejko We study the effect of quenched disorder on the semimetal-superconductor quantum phase transition in a model of two-dimensional Dirac semimetal with N flavors of two-component Dirac fermions, using perturbative renormalization group methods at one-loop order in a double epsilon expansion. For N ≥ 2 we... [Phys. Rev. B 98, 195142] Published Fri Nov 30, 2018

Description: Author(s): I. Valmianski, P. Y. Wang, S. Wang, Juan Gabriel Ramirez, S. Guénon, and Ivan K. Schuller We report the existence of two competing mechanisms in the current-driven electrical breakdown of vanadium sesquioxide ( V 2 O 3 ) and vanadium dioxide ( V O 2 ) nanodevices. Our experiments and simulations show that the competition between a purely electronic (PE) mechanism and an electrothermal (ET) mechan... [Phys. Rev. B 98, 195144] Published Fri Nov 30, 2018

Description: Author(s): Sumit Mazumdar We present a valence transition model for electron- and hole-doped cuprates, within which there occurs a discrete jump in ionicity Cu 2 + → Cu 1 + in both families upon doping, at or near optimal doping in the conventionally prepared electron-doped compounds and at the pseudogap phase transition in the ho... [Phys. Rev. B 98, 205153] Published Fri Nov 30, 2018

Description: Author(s): Vedran Jovic, Roland J. Koch, Swarup K. Panda, Helmuth Berger, Philippe Bugnon, Arnaud Magrez, Kevin E. Smith, Silke Biermann, Chris Jozwiak, Aaron Bostwick, Eli Rotenberg, and Simon Moser The efficiency and stability of RuO 2 in electrocatalysis has made this material a subject of intense fundamental and industrial interest. The surface functionality is rooted in its electronic and magnetic properties, determined by a complex interplay of lattice-, spin-rotational, and time-reversal s... [Phys. Rev. B 98, 241101(R)] Published Mon Dec 03, 2018

Description: Author(s): Iman Mahyaeh and Eddy Ardonne In this paper, we generalized the Peschel-Emery line of the interacting transverse field Ising model to a model based on three-state clock variables. Along this line, the model has exactly degenerate ground states, which can be written as product states. In addition, we present operators that transf... [Phys. Rev. B 98, 245104] Published Mon Dec 03, 2018

Description: Author(s): V. Brouet, L. Serrier-Garcia, A. Louat, L. Fruchter, F. Bertran, P. Le Fèvre, J. Rault, A. Forget, and D. Colson In Sr 2 IrO 4 and Sr 3 Ir 2 O 7 , correlations, magnetism, and spin-orbit coupling compete on similar energy scales, creating a new context to study metal-insulator transitions (MIT). We use here angle-resolved photoemission to investigate the MIT as a function of hole and electron doping in Sr 3 Ir 2 O 7 , obtain... [Phys. Rev. B 98, 235101] Published Mon Dec 03, 2018

Description: Author(s): Thomas Mertz, Karim Zantout, and Roser Valentí We introduce the concept of self-energy dispersion as an error bound on local theories and apply it to the two-dimensional Hubbard model on the square lattice at half filling. Since the self-energy has no single-particle analog and is not directly measurable in experiments, its general behavior as a... [Phys. Rev. B 98, 235105] Published Mon Dec 03, 2018

Description: Author(s): P. Thunström, O. Gunnarsson, Sergio Ciuchi, and G. Rohringer The local two-particle Green’s function and its generalized susceptibility are central building blocks in state-of-the-art theoretical descriptions of strongly correlated many-electron systems. The unexpected discovery of singular points in the generalized susceptibility, resulting in divergences of the two-particle irreducible vertex function and in multivaluedness of the Luttinger-Ward functional, has therefore attracted considerable interest. Unfortunately, almost no analytical results for irreducible vertices are available for correlated electrons. Here, the authors fill this gap by presenting fully analytical expressions for all irreducible vertex function of a simple, yet prototypical, correlated model, the single-orbital Hubbard atom. This gives highly relevant insights into the energy dependence of these functions. [Phys. Rev. B 98, 235107] Published Mon Dec 03, 2018

Description: Author(s): Sander H. Kooi, Guido van Miert, and Carmine Ortix We prove the existence of higher-order topological insulators with protected chiral hinge modes in quasi-two-dimensional systems made out of coupled layers stacked in an inversion-symmetric manner. In particular, we show that a homogeneous external magnetic field slightly tilted away from the stacki... [Phys. Rev. B 98, 245102] Published Mon Dec 03, 2018

Description: Author(s): Jörn W. F. Venderbos and Rafael M. Fernandes The recent observation of superconductivity in proximity to an insulating phase in twisted bilayer graphene (TBG) at small “magic” twist angles has been linked to the existence of nearly flat bands, which make TBG a fresh playground to investigate the interplay between correlations and superconducti... [Phys. Rev. B 98, 245103] Published Mon Dec 03, 2018

Description: Author(s): Hongkee Yoon, Jae-Hoon Sim, and Myung Joon Han We present a machine-learning approach to a long-standing issue in quantum many-body physics, namely, analytic continuation. This notorious ill-conditioned problem of obtaining spectral function from an imaginary time Green's function has been a focus of new method developments for past decades. Her... [Phys. Rev. B 98, 245101] Published Mon Dec 03, 2018

Description: Author(s): Xiaoting Zhou, Chuang-Han Hsu, Tay-Rong Chang, Hung-Ju Tien, Qiong Ma, Pablo Jarillo-Herrero, Nuh Gedik, Arun Bansil, Vitor M. Pereira, Su-Yang Xu, Hsin Lin, and Liang Fu Topological crystalline insulators (TCIs) are insulating electronic phases of matter with nontrivial topology originating from crystalline symmetries. Recent theoretical advances have proposed new TCI states protected by rotational symmetries and provided powerful guidelines to search for TCIs in re... [Phys. Rev. B 98, 241104(R)] Published Tue Dec 04, 2018

Description: Author(s): Lang Peng, Jing-Jing Xian, Peizhe Tang, Angel Rubio, Shou-Cheng Zhang, Wenhao Zhang, and Ying-Shuang Fu Freestanding single bilayer Bi(111) is a two-dimensional topological insulator with edge states propagating along its perimeter. Given the interlayer coupling experimentally, the topological nature of Bi(111) thin films and the impact of the supporting substrate on the topmost Bi bilayer are still u... [Phys. Rev. B 98, 245108] Published Wed Dec 05, 2018

Description: Author(s): J. Sánchez-Barriga, I. Aguilera, L. V. Yashina, D. Y. Tsukanova, F. Freyse, A. N. Chaika, C. Callaert, A. M. Abakumov, J. Hadermann, A. Varykhalov, E. D. L. Rienks, G. Bihlmayer, S. Blügel, and O. Rader The authors investigate the electronic and spin structure of topological surface states across a topological quantum phase transition. They find a surface band gap opening at the Dirac point of the topological surface states, giving rise to massive fermions with nonzero spin polarization on both sides of the phase transition. A mechanism of bulk-mediated scattering processes that increase with decreasing spin-orbit coupling strength is proposed as an explanation for the problem of the unconventional transformation between spin Dirac phases. [Phys. Rev. B 98, 235110] Published Wed Dec 05, 2018

Description: Author(s): Janis Erdmanis, Árpád Lukács, and Yuli V. Nazarov A variety of quantum systems exhibit Weyl points in their spectra where two bands cross in a point of three-dimensional parameter space with conical dispersion in the vicinity of the point. We consider theoretically the soft constraint regime where the parameters are dynamical quantum variables. We ... [Phys. Rev. B 98, 241105(R)] Published Wed Dec 05, 2018

Description: Author(s): Kamil Czelej, Marcin Roland Zemła, Piotr Śpiewak, and Krzysztof J. Kurzydłowski Hydrogen plays an essential role in the growth process of artificial diamond and can easily form complexes with lattice vacancies. Despite substantial efforts to resolve the electronic structure and the ground-state properties of the hydrogen-vacancy (HV) center, the final remarks are ambiguous, whi... [Phys. Rev. B 98, 235111] Published Thu Dec 06, 2018

Description: Author(s): Tao Zhu, Paolo E. Trevisanutto, Teguh Citra Asmara, Lei Xu, Yuan Ping Feng, and Andrivo Rusydi Recently, an anomalous generation of multiple plasmons with large spectral weight transfer in the visible to ultraviolet range (energies below the band gap) has been experimentally observed in the insulatinglike phase of oxygen-rich strontium niobium oxides ( SrNbO 3 + δ ). Here, we investigate the groun... [Phys. Rev. B 98, 235115] Published Fri Dec 07, 2018

Description: Author(s): O. Abdurazakov, D. Nevola, A. Rustagi, J. K. Freericks, D. B. Dougherty, and A. F. Kemper We study the role of excited phonon populations in the relaxation rates of nonequilibrium electrons using a nonequilibrium Green's function formalism. The transient modifications in the phononic properties are accounted for by self-consistently solving the Dyson equation for the electron and phonon ... [Phys. Rev. B 98, 245110] Published Fri Dec 07, 2018

Description: Author(s): Trithep Devakul, Dominic J. Williamson, and Yizhi You We consider symmetry-protected topological (SPT) phases in two dimensions protected by linear subsystem symmetries, i.e., those that act along rigid lines. There is a distinction between a “strong” subsystem SPT phase and a “weak” one, which is composed of decoupled one-dimensional SPTs with global ... [Phys. Rev. B 98, 235121] Published Mon Dec 10, 2018

Description: Author(s): D.-R. Tan and F.-J. Jiang The quantum critical regimes (QCR) of both a two-dimensional (2D) disordered spin- 1 2 antiferromagnet and a 2D clean dimerized quantum Heisenberg model are studied using the first-principles nonperturbative quantum Monte Carlo simulations. In particular, the three well-known universal coefficients as... [Phys. Rev. B 98, 245111] Published Mon Dec 10, 2018

Description: Author(s): Mathias S. Scheurer and Subir Sachdev We describe square lattice spin liquids, which break time-reversal symmetry, while preserving translational symmetry. The states are distinguished by the manner in which they transform under mirror symmetries. All the states have nonzero scalar spin chirality, which implies the appearance of spontan... [Phys. Rev. B 98, 235126] Published Tue Dec 11, 2018

Description: Author(s): V. N. Antonov, S. Uba, and L. Uba We studied the electronic, magnetic, and optical properties of β − Li 2 IrO 3 insulator within the density-functional theory using the generalized gradient approximation taking into account strong Coulomb correlations (GGA+ U ) in the framework of the fully relativistic spin-polarized Dirac linear muffin-t... [Phys. Rev. B 98, 245113] Published Tue Dec 11, 2018

Description: Author(s): S. Saberi-Pouya, M. Zarenia, T. Vazifehshenas, and F. M. Peeters The possibility of an inhomogeneous charge density wave phase is investigated in a system of two coupled electron and hole monolayers separated by a hexagonal boron nitride insulating layer. The charge-density-wave state is induced through the assumption of negative compressibility of electron/hole ... [Phys. Rev. B 98, 245115] Published Wed Dec 12, 2018

Description: Author(s): Vladyslav Kozii and Liang Fu We study the inelastic scattering rate due to the Coulomb interaction in three-dimensional Dirac/Weyl semimetals at finite temperature. We show that the perturbation theory diverges because of the long-range nature of the interaction, hence, thermally induced screening must be taken into account. We... [Phys. Rev. B 98, 041109(R)] Published Tue Jul 24, 2018

Description: Author(s): A. Baum, Ying Li, M. Tomić, N. Lazarević, D. Jost, F. Löffler, B. Muschler, T. Böhm, J.-H. Chu, I. R. Fisher, R. Valentí, I. I. Mazin, and R. Hackl We report results of Raman scattering experiments on twin-free BaFe 2 As 2 with the main focus placed on understanding the influence of electronic and spin degrees of freedom on the lattice dynamics. In particular, we scrutinize the E g modes and the As A 1 g mode. Each of the two E g phonons in the tetrag... [Phys. Rev. B 98, 075113] Published Tue Aug 07, 2018

Description: Author(s): I. V. Silkin, I. P. Chernov, V. M. Silkin, and E. V. Chulkov Electron excitation spectra in Ti and Zr transition metals are calculated in the framework of time-dependent density functional theory. Several peaks found in the obtained loss functions are interpreted as collective excitations. The energy positions of the dominating bulk plasmons are in close agre... [Phys. Rev. B 98, 075111] Published Tue Aug 07, 2018

Description: Author(s): A. Viviana Gómez, Ferney J. Rodríguez, and Luis Quiroga Nitrogen-vacancy (NV) defect centers in diamond are strong candidates to generate entangled states in solid-state environments even at room temperature. Quantum correlations in spatially separated NV systems, for distances between NVs ranging from a few nanometers to a few kilometers, have been rece... [Phys. Rev. B 98, 075114] Published Tue Aug 07, 2018

Description: Author(s): N. Katayama, S. Tamura, T. Yamaguchi, K. Sugimoto, K. Iida, T. Matsukawa, A. Hoshikawa, T. Ishigaki, S. Kobayashi, Y. Ohta, and H. Sawa We discuss herein the emergence of a large entropy change in metallic Li 0.33 VS 2 derived from orbitally assisted loose σ bond formation. Comprehensive structural studies based on synchrotron x-ray and neutron diffraction analyses clarify the fabrication of ribbon chains at 375 K, consisting of multip... [Phys. Rev. B 98, 081104(R)] Published Tue Aug 07, 2018

Description: Author(s): Franziska Weickert, Philipp Gegenwart, Christoph Geibel, Wolf Assmus, and Frank Steglich We present thermal expansion and magnetostriction measurements on a CeCu 2 Si 2 single crystal of A/S type up to 17.9 T magnetic field applied along the crystallographic a direction ( Δ L ∥ a ∥ H ) and down to 0.015 K temperature. We identify clear thermodynamic anomalies at the superconducting transition T c ... [Phys. Rev. B 98, 085115] Published Wed Aug 08, 2018

Description: Author(s): Kohei Kawabata, Yuto Ashida, Hosho Katsura, and Masahito Ueda Nonequilibrium open systems effectively described by non-Hermitian Hamiltonians with parity-time ( P T ) symmetry have recently attracted considerable attention due to their properties with no Hermitian counterparts. In particular, there exists a growing interest in non-Hermitian topological phases of matter. Here, the authors show that a P T -symmetric topological superconducting wire possesses two distinct types of unconventional edge modes, those with complex energies and with nonorthogonal Majorana zero modes. The latter induce anomalous particle transport with nonlocal currents present only at the edges. This work explores a unique nonequilibrium topological phenomenon that results from the interplay between P T symmetry and topological superconductivity. [Phys. Rev. B 98, 085116] Published Wed Aug 08, 2018

Description: Author(s): Tianbai Cui and Rafael M. Fernandes The concept of a vestigial nematic order emerging from a “mother” spin or charge-density-wave state has been applied to describe the phase diagrams of several systems, including unconventional superconductors. In a perfectly clean system, the two orders appear simultaneously via a first-order quantu... [Phys. Rev. B 98, 085117] Published Wed Aug 08, 2018

Description: Author(s): Jonas Heverhagen and Maria Daghofer We study the impact of Hund's-rule coupling on orbital excitations, as, e.g., measured in inelastic resonant x-ray scattering. We find that the interpretation in terms of spin-orbit separation, which has been derived for one-dimensional systems without Hund's rule, remains robust in its presence. De... [Phys. Rev. B 98, 085120] Published Thu Aug 09, 2018

Description: Author(s): Krzysztof Rościszewski and Andrzej M. Oleś Using the multiband d − p model and unrestricted Hartree-Fock approximation we investigate the electronic structure and spin-orbital order in a three-dimensional VO 3 lattice. The main aim of this paper is testing if a simple d − p model with partly filled 3 d orbitals (in vanadium ions) and 2 p orbitals (... [Phys. Rev. B 98, 085119] Published Thu Aug 09, 2018

Description: Author(s): John W. Villanova and Kyungwha Park Weyl semimetals (WSMs) have Weyl nodes where conduction and valence bands meet in the absence of inversion or time-reversal symmetry (TRS) or both. The TRS-broken WSM phase can be driven from a topological Dirac semimetal by magnetic field B or magnetic dopants, considering that Dirac semimetals hav... [Phys. Rev. B 98, 075123] Published Mon Aug 13, 2018

Description: Author(s): Kazumasa Miyake and Shinji Watanabe Recently, it was reported by MacLaughlin et al. in Phys. Rev. B 93 , 214421 (2016) that α − YbAl 0.986 Fe 0.014 B 4 exhibits an anomalous temperature dependence in the relaxation rate 1 / T 1 of μ SR , and stressed that such temperature dependence cannot be understood by the scenario based on the quantum critica... [Phys. Rev. B 98, 075125] Published Tue Aug 14, 2018

Description: Author(s): Sergey Slizovskiy, Pablo Rodriguez-Lopez, and Joseph J. Betouras We apply the self-consistent renormalized perturbation theory to the Hubbard model on the square lattice at finite temperatures to study the evolution of the Fermi surface (FS) as a function of temperature and doping. Previously, a nematic phase for the same model has been reported to appear at weak... [Phys. Rev. B 98, 075126] Published Tue Aug 14, 2018

Description: Author(s): Emanuel Gull, Sergei Iskakov, Igor Krivenko, Alexander A. Rusakov, and Dominika Zgid Problems of finite-temperature quantum statistical mechanics can be formulated in terms of imaginary (Euclidean) -time Green's functions and self-energies. In the context of realistic Hamiltonians, the large energy scale of the Hamiltonian (as compared to temperature) necessitates a very precise rep... [Phys. Rev. B 98, 075127] Published Wed Aug 15, 2018

Description: Author(s): Moritz August and Mari Carmen Bañuls Building on a previously introduced block Lanczos method, we demonstrate how to approximate any operator function of the form Tr f ( A ) when the argument A is given as a Hermitian matrix product operator (MPO). This gives access to quantities that, depending on the full spectrum, are difficult to acces... [Phys. Rev. B 98, 075128] Published Wed Aug 15, 2018

Description: Author(s): José A. S. Lourenço, Ronivon L. Eneias, and Rodrigo G. Pereira The combination of non-Hermitian physics and strong correlations can give rise to new effects in open quantum many-body systems with balanced gain and loss. We propose a generalized Anderson impurity model that includes non-Hermitian hopping terms between an embedded quantum dot and two wires. These... [Phys. Rev. B 98, 085126] Published Wed Aug 15, 2018