ALBERT

Description: Author(s): C. Van Vlack, Peijun Yao, and S. Hughes We present a study of light-induced forces between two coupled plasmonic nanoparticles above various slab geometries including a metallic half-space and a negative index material (NIM) slab waveguide. We investigate optical forces by nonperturbatively calculating the scattered electric field via a G... [Phys. Rev. B 83, 245404] Published Fri Jun 17, 2011

Description: Author(s): Pouyan Ghaemi, Sarang Gopalakrishnan, and Taylor L. Hughes Graphene was the first material predicted to be a time-reversal-invariant topological insulator [ C. L. Kane and E. J. Mele Phys. Rev. Lett. 95 226801 (2005) ]; however, the insulating gap is immeasurably small owing to the weakness of spin-orbit interactions in graphene. A recent experiment [ K. K.... [Phys. Rev. B 86, 201406] Published Wed Nov 14, 2012

Description: Author(s): Qinglei Meng, Smitha Vishveshwara, and Taylor L. Hughes We study the dynamics of a quantum spin Hall edge coupled to a magnet with its own dynamics. Using spin-transfer-torque principles, we analyze the interplay between spin currents in the edge state and dynamics of the axis of the magnet, and draw parallels with circuit analogies. As a highlighting fe... [Phys. Rev. B 90, 205403] Published Thu Nov 06, 2014

Description: Author(s): Gerasimos Angelatos and Stephen Hughes We introduce a platform for realizing on-chip quantum electrodynamics using photonic-crystal waveguide structures composed of periodic nanowire arrays with embedded semiconductor quantum dots to act as quantum light sources. These nanowire-based structures, which can now be fabricated with excellent... [Phys. Rev. B 90, 205406] Published Fri Nov 07, 2014

Description: Author(s): Yi-Ting Hsu, Mark H. Fischer, Taylor L. Hughes, Kyungwha Park, and Eun-Ah Kim Identifying the effects of surface-bulk coupling is a key challenge in exploiting the topological nature of the surface states in many available three-dimensional topological “metals.” Here we combine an effective-model calculation and an ab initio slab calculation to study the effects of the lowest... [Phys. Rev. B 89, 205438] Published Thu May 29, 2014

Description: Author(s): Ebrahim Forati, George W. Hanson, and Stephen Hughes Using a realistic quantum master equation, we show that the resonance fluorescence spectra of a two-level artificial atom (quantum dot) can be tuned by adjusting its photonic local density of states via biasing one or more graphene monolayers. The structured photon reservoir is included using a phot... [Phys. Rev. B 90, 085414] Published Tue Aug 12, 2014

Description: Author(s): Brian Dellabetta, Taylor L. Hughes, Matthew J. Gilbert, and Benjamin L. Lev Ultracold and quantum degenerate gases held near conductive surfaces can serve as sensitive, high-resolution, and wide-area probes of electronic current flow. Previous work has imaged transport around grain boundaries in a gold wire by using ultracold and Bose-Einstein condensed atoms held microns f... [Phys. Rev. B 85, 205442] Published Thu May 24, 2012

Description: Author(s): Hsiang-Hsuan Hung, Pouyan Ghaemi, Taylor L. Hughes, and Matthew J. Gilbert Majorana fermions are predicted to play a crucial role in condensed matter realizations of topological quantum computation. These heretofore undiscovered quasiparticles have been predicted to exist at the cores of vortex excitations in topological superconductors and in heterostructures of supercond... [Phys. Rev. B 87, 035401] Published Wed Jan 02, 2013

Description: The future space-based gravitational wave detector LISA will be able to measure parameters of coalescing massive black hole binaries, often to extremely high accuracy. Previous work has demonstrated that the black hole spins can have a strong impact on the accuracy of parameter measurement. Relativistic spin-induced precession modulates the waveform in a manner which can break degeneracies between parameters, in principle significantly improving how well they are measured. Recent studies have indicated, however, that spin precession may be weak for an important subset of astrophysical binary black holes: those in which the spins are aligned due to interactions with gas. In this paper, we examine how well a binary's parameters can be measured when its spins are partially aligned and compare results using waveforms that include higher post-Newtonian harmonics to those that are truncated at leading quadrupole order. We find that the weakened precession can substantially degrade parameter estimation, particularly for the "extrinsic" parameters sky position and distance. Absent higher harmonics, LISA typically localizes the sky position of a nearly aligned binary about an order of magnitude less accurately than one for which the spin orientations are random. Our knowledge of a source's sky position will thus be worst for the gas-rich systems which are most likely to produce electromagnetic counterparts. Fortunately, higher harmonics of the waveform can make up for this degradation. By including harmonics beyond the quadrupole in our waveform model, we find that the accuracy with which most of the binary's parameters are measured can be substantially improved. In some cases, the improvement is such that they are measured almost as well as when the binary spins are randomly aligned.

Description: The 30 Myr old A3-type star HD 21997 is one of the two known debris dust disks having a measurable amount of cold molecular gas. With the goal of understanding the physical state, origin, and evolution of the gas in young debris disks, we obtained CO line observations with the Atacama Large Millimeter/submillimeter Array (ALMA). Here, we report on the detection of (12)CO and (13)CO in the J = 2-1 and J = 3-2 transitions and C(18)O in the J = 2-1 line. The gas exhibits a Keplerian velocity curve, one of the few direct measurements of Keplerian rotation in young debris disks. The measured CO brightness distribution could be reproduced by a simple star+disk system, whose parameters are r(sub in) 〈 26 AU, r(sub out) = 138 +/- 20 AU, Stellar M = 1.8 +0.5/0.2 Solar M, and i = 32. Deg. 6 +/- 3 deg..1. The total CO mass, as calculated from the optically thin C(18)O line, is about (4-8) 10(exp 2 ) Solar M, while the CO line ratios suggest a radiation temperature on the order of 6-9 K. Comparing our results with those obtained for the dust component of the HD 21997 disk from ALMA continuum observations by Moor et al., we conclude that comparable amounts of CO gas and dust are present in the disk. Interestingly, the gas and dust in the HD 21997 system are not colocated, indicating a dust-free inner gas disk within 55 AU of the star. We explore two possible scenarios for the origin of the gas. A secondary origin, which involves gas production from colliding or active planetesimals, would require unreasonably high gas production rates and would not explain why the gas and dust are not colocated. We propose that HD 21997 is a hybrid system where secondary debris dust and primordial gas coexist. HD 21997, whose age exceeds both the model predictions for disk clearing and the ages of the oldest T Tauri-like or transitional gas disks in the literature, may be a key object linking the primordial and the debris phases of disk evolution.