Relative Strength Of Disorder Research Articles

Dynamical signatures of Chaos to integrability crossover in generalized random matrix ensembles

We introduce a two-parameter ensemble of generalized real symmetric random matrices called the β-Rosenzweig–Porter ensemble (β-RPE), parameterized by β, a fictitious inverse temperature of the analogous Coulomb gas model, and γ, controlling the relative strength of disorder. β-RPE encompasses RPE from all of the Dyson’s threefold symmetry classes: orthogonal, unitary and symplectic for . Firstly, we study the energy correlations by calculating the density and 2nd moment of the nearest neighbor spacing (NNS) and robustly quantify the crossover among various degrees of level repulsions. Secondly, the dynamical properties are determined from an exact calculation of the temporal evolution of the fidelity enabling an identification of the characteristic Thouless and the equilibration timescales. The relative depth of the correlation hole in the average fidelity serves as a dynamical signature of the crossover from chaos to integrability and enables us to construct the phase diagram of β-RPE in the γ-β plane. Our results are in qualitative agreement with numerically computed fidelity for matrix ensembles. Furthermore, we observe that for large N the 2nd moment of NNS and the relative depth of the correlation hole exhibit a second order phase transition at γ = 2.

Sign change of competing contributions to the side jump by impurity, phonon, and magnon scattering

The side jump is one important mechanism of anomalous Hall effect, which is generally believed that it does not depend on the scattering strength and disorder density. Recent theoretical calculations indicate that different types of disordered scattering contribute to side jump. The competition between them will make the magnitude of side jump sensitive to their relative disorder strength. However, the evolution of competing scattering contribution in side jump has not been experimentally observed. In this paper, a series of high-qulity FeCo films with different thickness have been grown on MgO(001) substrate. Based on multivariable scaling, the sign change of the competing contribution between different scatterings to side jump is clearly observed as increasing sample thickness. Meanwhile, we demonstrate that the contribution of magnon side jump may play an irreplaceable role in the competition. Our work provides evidence for the shift of dominated scattering in competition, and shows that competing scattering still exists and is not negligible even in conductivity region with ${\ensuremath{\sigma}}_{xx}\ensuremath{\sim}{10}^{4}\phantom{\rule{0.16em}{0ex}}{\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}1}\phantom{\rule{0.16em}{0ex}}\mathrm{c}{\mathrm{m}}^{\ensuremath{-}1}$, which is beneficial to further experimental and theoretical studies of side jump.

Classification of Intensity Distributions of Transmission Eigenchannels of Disordered Nanophotonic Structures Using Machine Learning

Light-matter interaction optimization in complex nanophotonic structures is a critical step towards the tailored performance of photonic devices. The increasing complexity of such systems requires new optimization strategies beyond intuitive methods. For example, in disordered photonic structures, the spatial distribution of energy densities has large random fluctuations due to the interference of multiply scattered electromagnetic waves, even though the statistically averaged spatial profiles of the transmission eigenchannels are universal. Classification of these eigenchannels for a single configuration based on visualization of intensity distributions is difficult. However, successful classification could provide vital information about disordered nanophotonic structures. Emerging methods in machine learning have enabled new investigations into optimized photonic structures. In this work, we combine intensity distributions of the transmission eigenchannels and the transmitted speckle-like intensity patterns to classify the eigenchannels of a single configuration of disordered photonic structures using machine learning techniques. Specifically, we leverage supervised learning methods, such as decision trees and fully connected neural networks, to achieve classification of these transmission eigenchannels based on their intensity distributions with an accuracy greater than 99%, even with a dataset including photonic devices of various disorder strengths. Simultaneous classification of the transmission eigenchannels and the relative disorder strength of the nanophotonic structure is also possible. Our results open new directions for machine learning assisted speckle-based metrology and demonstrate a novel approach to classifying nanophotonic structures based on their electromagnetic field distributions. These insights can be of paramount importance for optimizing light-matter interactions at the nanoscale.

Barrier or easy-flow channel: The role of grain boundary acting on vortex motion in type-II superconductors* *Project supported financially by the National Natural Science Foundation of China (Grant No. 12072101) and the Fundamental Research Funds for the Central Universities, China (Grant No. 2018B48714).

Grain boundaries (GBs), as extremely anisotropic pinning defects, have a strong impact on vortex motion in type-II superconductors, and further on the macro level dominates the superconductivity for example the critical current density. Many previous studies indicated that mostly GB plays the role of a strong barrier for vortex motion, while an easy-flow channel just under some certain conditions. In order to thoroughly make clear of the questions of what is exactly the role of GB on vortex motion and how it works, in this article we developed a large scale molecular dynamic model and revealed the action of GB on vortex motion in type-II superconductors. The most significant finding is that the role of GB on vortex motion can be changeable from a barrier to an easy-flow channel, and which is intrinsically determined by the competition effect correlated with its action on vortex between in the GB and no-GB regions. Such the competition effect essentially depends on the attributes of both the GB (described by the GB strength and angle θ) and no-GB pining regions (by the relative disorder strength α p/α v). Specifically, for a YBa2Cu3O7 – x (YBCO) sample, to obtain a clear knowledge of vortex motion in GB region, we visualized the three typical trajectories of vortices during the three vortex movement stages. Further, in order to understand how GB results in the macro current-carrying property, corresponding to the current–voltage relation of the YBCO conductor, we obtained the average velocity vy of vortices varying with their driving force, which is nearly identical with the previous observations.

Transition from trap-mediated to band-like transport in polycrystalline monolayer molybdenum disulfide memtransistors

Multi-terminal memtransistors using polycrystalline monolayer molybdenum disulfide (MoS2) have recently emerged as novel synaptic devices. Due to the coexistence of disorder and strong Coulomb carrier-carrier interactions in MoS2, localization and delocalization of carriers can come into play successively upon the relative strength of disorder and interactions, which can be tuned by the Fermi level (EF). In this work, we show that the transition from trap-mediated to band-like transport leads to the resistive switching behavior in MoS2 memtransistors, which is driven by the EF shift arising from defect profile redistribution that is facilitated by grain boundaries. In the high resistance state, field-driven hopping conduction can be clearly observed in the high-field region (E>0.05 MV/cm), whereas the linear dependence of ln(I/E) on the square root of the electric field, E1/2, suggests Poole–Frenkel emission in the low-field region (E≤0.05 MV/cm). In the low resistance state, strong interactions prevailed and a substantial amount of thermally activated electrons are excited into the conduction band, leading to band-like transport.

Transport of correlated electrons through disordered chains: A perspective on entanglement, conductance, and disorder averaging

We investigate electron transport in disordered Hubbard chains contacted to macroscopic leads, via the non-equilibrium Green's functions technique. We observe a cross-over of currents and conductances at finite bias which depends on the relative strength of disorder and interactions. The finite-size scaling of the conductance is highly dependent on the interaction strength, and exponential attenuation is not always seen. We provide a proof that the Coherent Potential Approximation, a widely used method for treating disorder averages, fulfils particle conservation at finite bias with or without electron correlations. Finally, our results hint that the observed trends in conductance due to interactions and disorder also appear as signatures in the single-site entanglement entropy.

Scattering universality classes of side jump in the anomalous Hall effect

The anomalous Hall conductivity has an important extrinsic contribution known as side jump contribution, which is independent of both scattering strength and disorder density. Nevertheless, we discover that side jump has strong dependence on the spin structure of the scattering potential. We propose three universality classes of scattering for the side jump contribution, having the characters of being spin-independent, spin-conserving and spin-flip respectively. For each individual class, the side jump contribution takes a different unique value. When two or more classes of scattering are present, the value of side jump is no longer fixed but varies as a function of their relative disorder strength. As system control parameter such as temperature changes, due to the competition between different classes of disorder scattering, the side jump Hall conductivity could flow from one class dominated limit to another class dominated limit. Our result indicates that magnon scattering plays a role distinct from normal impurity scattering and phonon scattering in the anomalous Hall effect because they belong to different scattering classes.

Dominant Mobility Modulation by the Electric Field Effect at theLaAlO3/SrTiO3Interface

Caviglia et al. [Nature (London) 456, 624 (2008)] have found that the superconducting LaAlO3/SrTiO3 interface can be gate modulated. A central issue is to determine the principal effect of the applied electric field. Using magnetotransport studies of a gated structure, we find that the mobility variation is almost 5 times that of the sheet carrier density. Furthermore, superconductivity can be suppressed at both positive and negative gate bias. These results indicate that the relative disorder strength strongly increases across the superconductor-insulator transition.

Disorder Induced Transition into a One-Dimensional Wigner Glass

The destruction of quasi-long-range crystalline order as a consequence of strong disorder effects is shown to accompany the strict localization of all classical plasma modes of one-dimensional Wigner crystals at T=0. We construct a phase diagram that relates the structural phase properties of Wigner crystals to a plasmon delocalization transition recently reported. Deep inside the strictly localized phase of the strong disorder regime, we observe glasslike behavior. However, well into the critical phase with a plasmon mobility edge, the system retains its crystalline composition. We predict that a transition between the two phases occurs at a critical value of the relative disorder strength. This transition has an experimental signature in the ac conductivity as a local maximum of the largest spectral amplitude as a function of the relative disorder strength.

Density-dependent intersubband absorption in strongly disordered systems

We study theoretically the intersubband (IS) absorption spectrum of electrons in a center-doped quantum well (QW) as a function of the carrier density. Besides the subband quantization in z direction, the wave functions of the electrons, being directly exposed to the charged dopands, become disorder localized in the layer plane. For each set of random impurity configurations, the corresponding spectrum of quantum states is computed with a self-consistent density-functional approach, thus, taking into account the disorder and nonlinear static screening effects in a realistic way. On the basis of these effective single-particle states, we then include dynamic many-body effects (depolarization and dynamic exchange corrections) by applying and extending our recently developed theory of resonant screening in the localization regime. We analyze the relevance of the various many-body effects and find that at higher electron densities the direct static Hartree and the depolarization contributions dominate over the exchange effects. Dynamic Coulomb interactions qualitatively change the IS absorption spectrum of the statically screened electron gas, however, do not lead to a spectral narrowing in this system. A small variation of the $\ensuremath{\delta}n$-layer position within the QW affects the relative disorder strength of the two subbands and causes dramatic changes of the spectral shape and width. Our model and results are suitable for a direct comparison with experimental data.

Electronic transport in disordered interacting systems

AbstractWe numerically investigate the transport properties of disordered interacting electrons in three dimensions in the metallic as well as in the insulating phases. The disordered many‐particle problem is modeled by the quantum Coulomb glass which contains a random potential, long‐range unscreened Coulomb interactions and quantum hopping between different sites. We have recently developed the Hartree‐Fock based diagonalization (HFD) method which amounts to diagonalizing the Hamiltonian in a suitably chosen energetically truncated basis. This method allows us to investigate comparatively large systems. Here we calculate the combined effect of disorder and interactions on the dissipative conductance. We find that the qualitative influence of the interactions on the conductance depends on the relative disorder strength. For strong disorder interactions can significantly enhance the transport while they suppress the conductance for weak disorder.

Electronic transport in disordered interacting systems

We numerically investigate the transport properties of disordered interacting electrons in three dimensions in the metallic as well as in the insulating phases. The disordered many-particle problem is modeled by the quantum Coulomb glass which contains a random potential, long-range unscreened Coulomb interactions and quantum hopping between different sites. We have recently developed the Hartree-Fock based diagonalization (HFD) method which amounts to diagonalizing the Hamiltonian in a suitably chosen energetically truncated basis. This method allows us to investigate comparatively large systems. Here we calculate the combined effect of disorder and interactions on the dissipative conductance. We find that the qualitative influence of the interactions on the conductance depends on the relative disorder strength. For strong disorder interactions can significantly enhance the transport while they suppress the conductance for weak disorder.

Disorder scattering and electron mobility in Hg1-xCdxTe

The coherent potential approximation and a k.p alloy Hamiltonian are used to provide a detailed analysis of the influence of disorder scattering on the zone-centre band structure and the electron mobility in II-VI semiconductor alloys. The weak-scattering approximation to the electron mobility is shown to apply to the common II-VI alloys. The effect of alloy disorder on the zone-centre band structure of a zero-gap alloy is examined. The total electron mobility in the mixed-crystal system Hg1-xCdxTe is evaluated, and the relative strength of disorder scattering in comparison with other scattering mechanisms is assessed, for a range of impurity concentration and alloy composition.