ALBERT

Description: We investigate the electronic structure of a complex conventional superconductor, ZrB12 employing high resolution photoemission spectroscopy and ab initio band structure calculations. The experimental valence band spectra could be described reasonably well within the local density approximation. Energy bands close to the Fermi level possess t2g symmetry and the Fermi level is found to be in the proximity of quantum fluctuation regime. The spectral lineshape in the high resolution spectra is complex exhibiting signature of a deviation from Fermi liquid behavior. A dip at the Fermi level emerges above the superconducting transition temperature that gradually grows with the decrease in temperature. The spectral simulation of the dip and spectral lineshape based on a phenomenological self energy suggests finite electron pair lifetime and a pseudogap above the superconducting transition temperature. Scientific Reports 3 doi: 10.1038/srep03342

Description: Corrigendum Nature Communications doi: 10.1038/ncomms3355 Authors: Alexander D. Douglas, Andrew R. Williams, Joseph J. Illingworth, Gathoni Kamuyu, Sumi Biswas, Anna L. Goodman, David H. Wyllie, Cécile Crosnier, Kazutoyo Miura, Gavin J. Wright, Carole A. Long, Faith H. Osier, Kevin Marsh, Alison V. Turner, Adrian V. S. Hill, Simon J. Draper

Description: Crystalline solids undergo plastic deformation and subsequently flow when subjected to stresses beyond their elastic limit. In nature most crystalline solids exist in polycrystalline form. Simulating plastic flows in polycrystalline solids has wide ranging applications, from material processing to understanding intermittency of earthquake dynamics. Using phase field crystal (PFC) model we show that in sheared polycrystalline solids the atomic displacement field shows spatio-temporal heterogeneity spanning over several orders of length and time scales, similar to that in amorphous solids. The displacement field also exhibits localized quadrupolar patterns, characteristic of two dislocations of the opposite sign approaching each other. This is a signature of crystallinity at microscopic scale. Polycrystals being halfway between single crystals and amorphous solids, in terms of the degree of structural order, descriptions of solid mechanics at two widely different scales, namely continuum plastic flow and discrete dislocation dynamics turns out to be necessary here. Scientific Reports 3 doi: 10.1038/srep02728

Description: Here, we present x-ray resonant magnetic dichroism and x-ray resonant magnetic scattering measurements of the temperature dependence of magnetism in Pr-doped La-Ca-Mn-O films grown on (110) NdGaO 3 substrates. We observed thermal hysteresis of the ferromagnetism in one film that also showed large thermal hysteresis of ∼18 K in transport measurements. While in a second film of a different nominal chemistry, which showed very small thermal hysteresis ∼3 K in transport measurements, no thermal hysteresis of the ferromagnetism was observed. These macroscopic properties are correlated with evolution of surface magnetization across metal insulator transition for these films as observed by soft x-ray resonant magnetic scattering measurements.

Description: In this study, we have investigated the ion concentration dependent collective dynamics in two series of deep eutectic solvent (DES) systems by femtosecond Raman-induced Kerr effect spectroscopy, as well as some physical properties, e.g., shear viscosity ( η ), density ( ρ ), and surface tension ( γ ). The DES systems studied here are [0.75CH 3 CONH 2 + 0.25{ f  KSCN + (1 – f  )NaSCN}] and [0.78CH 3 CONH 2 + 0.22{ f  LiBr + (1 – f  )LiNO 3 }] with f = 0, 0.2, 0.4, 0.6, 0.8, and 1.0. γ of these DES systems shows near insensitivity to f , while ρ shows a moderate dependence on f . Interestingly, η exhibits a strong dependence on f . In the low-frequency Kerr spectra, obtained via the Fourier transform of the collected Kerr transients, a characteristic band at ∼70 cm −1 is clear in [0.78CH 3 CONH 2 + 0.22{ f  LiBr + (1 – f  )LiNO 3 }] DES especially at the larger f . The band is attributed to the intermolecular hydrogen bond of acetamide. Because of less depolarized Raman activities of intermolecular/interionic vibrational motions, which are mostly translational (collision-induced or interaction-induced) motions, of spherical ions, the intermolecular hydrogen-bonding band is clearly observed. In contrast, the intermolecular hydrogen-bonding band is buried in the other intermolecular/interionic vibrational motions, which includes translational and reorientational (librational) motions and their cross-terms, in [0.75CH 3 CONH 2 + 0.25{ f  KSCN + (1 – f  )NaSCN}] system. The first moment ( M 1 ) of the intermolecular/interionic vibrational band in these DES systems is much higher than that in typical neutral molecular liquids and shows a weak but contrasting dependence on the bulk parameter γ / ρ . The time constants for picosecond overdamped Kerr transients in both the DES systems, which are obtained on the basis of the analysis fitted by a triexponential function, are rather insensitive to f for both the DES systems, but all the three time constants (fast: ∼1–3 ps; intermediate: ∼7–20 ps; and slow: ∼100 ps) are different between the [0.78CH 3 CONH 2 + 0.22{ f  LiBr + (1 – f  )LiNO 3 }] and [0.75CH 3 CONH 2 + 0.25{ f  KSCN + (1 – f  )NaSCN}] systems. These results indicate that the intermolecular/interionic interactions in DES systems is strongly influenced by the ionic species present in these DES systems.

Description: Rugged energy landscapes find wide applications in diverse fields ranging from astrophysics to protein folding. We study the dependence of diffusion coefficient ( D ) of a Brownian particle on the distribution width (ɛ) of randomness in a Gaussian random landscape by simulations and theoretical analysis. We first show that the elegant expression of Zwanzig [Proc. Natl. Acad. Sci. U.S.A.85, 2029 (1988)] for D (ɛ) can be reproduced exactly by using the Rosenfeld diffusion-entropy scaling relation. Our simulations show that Zwanzig's expression overestimates D in an uncorrelated Gaussian random lattice – differing by almost an order of magnitude at moderately high ruggedness. The disparity originates from the presence of “three-site traps” (TST) on the landscape – which are formed by the presence of deep minima flanked by high barriers on either side. Using mean first passage time formalism, we derive a general expression for the effective diffusion coefficient in the presence of TST, that quantitatively reproduces the simulation results and which reduces to Zwanzig's form only in the limit of infinite spatial correlation. We construct a continuous Gaussian field with inherent correlation to establish the effect of spatial correlation on random walk. The presence of TSTs at large ruggedness (ɛ ≫ k B T ) gives rise to an apparent breakdown of ergodicity of the type often encountered in glassy liquids.

Description: A time dependent thermal model for a superconducting constriction based weak-link (WL) is discussed for investigating the deterministic dynamics of its temperature and phase. A new dynamic regime is found where a non-zero voltage exists across the WL, and its temperature stabilizes between the bath temperature and superconductor's critical temperature. This regime exists over a limited bias current range and gives rise to a new hysteretic regime in current-voltage characteristics. We also discuss the effect of fluctuations on the current-voltage characteristics and experimental implications of this dynamic regime.

Description: A semi-molecular theory for studying composition dependent Stokes shift dynamics of a dipolar solute in binary mixtures of (non-dipolar ionic liquid + common dipolar solvent) is developed here. The theory provides microscopic expressions for solvation response functions in terms of static and dynamic structure factors of the mixture components and solute-solvent static correlations. In addition, the theory provides a framework for examining the interrelationship between the time dependent solvation response in and frequency dependent dielectric relaxation of a binary mixture containing electrolyte. Subsequently, the theory has been applied to predict ionic liquid (IL) mole fraction dependent dynamic Stokes shift magnitude and solvation energy relaxation for a dipolar solute, C153, in binary mixtures of an ionic liquid, trihexyltetradecylphosphonium chloride ([P 14,666 ][Cl]) with a common dipolar solvent, methanol (MeOH). In the absence of suitable experimental data, necessary input parameters have been obtained from approximate methods. Dynamic shifts calculated for these mixtures exhibit a linear increase with IL mole fraction for the most part of the mixture composition, stressing the importance of solute-IL dipole-ion interaction. Average solvation rates, on the other hand, show a nonlinear IL mole fraction dependence which is qualitatively similar to what has been observed for such binary mixtures with imidazolium (dipolar) ILs. These predictions should be re-examined in suitable experiments.

Description: Understanding of metal insulator transitions in a strongly correlated system, driven by Anderson localization (disorder) and/or Mott localization (correlation), is a long standing problem in condensed matter physics. The prevailing fundamental question would be how these two mechanisms contrive to accomplish emergent anomalous behaviors. Here, we have grown high quality perovskite SrIrO 3 thin films, containing a strong spin orbit coupled 5 d element Ir, on various substrates such as GdScO 3 (110), DyScO 3 (110), SrTiO 3 (001), and NdGaO 3 (110) with increasing lattice mismatch, in order to carry out a systematic study on the transport properties. We found that metal insulator transitions can be induced in this system; by either reducing thickness (on best lattice matched substrate) or changing degree of lattice strain (by lattice mismatch between film and substrates) of films. Surprisingly these two pathways seek two distinct types of metal insulator transitions; the former falls into disorder driven Anderson type whereas the latter turns out to be of unconventional Mott-Anderson type with the interplay of disorder and correlation. More interestingly, in the metallic phases of SrIrO 3 , unusual non-Fermi liquid characteristics emerge in resistivity as Δ ρ ∝ T ε with ε evolving from 4/5 to 1 to 3/2 with increasing lattice strain. We discuss theoretical implications of these phenomena to shed light on the metal insulator transitions.