Disorder Strength Research Articles

Scaling behavior of the localization length for TE waves at critical incidence on short-range correlated stratified random media

We theoretically investigate the scaling behavior of the localization length for s-polarized electromagnetic waves incident at a critical angle on stratified random media with short-range correlated disorder. By employing the invariant embedding method, extended to waves in correlated random media, and utilizing the Shapiro–Loginov formula of differentiation, we accurately compute the localization length ξ of s waves incident obliquely on stratified random media that exhibit short-range correlated dichotomous randomness in the dielectric permittivity. The random component of the permittivity is characterized by the disorder strength parameter σ2 and the disorder correlation length lc. Away from the critical angle, ξ depends on these parameters independently. However, precisely at the critical angle, we discover that for waves with wavenumber k, kξ depends on the single parameter klcσ2, satisfying a universal equation kξ≈1.3717klcσ2−1/3 across the entire range of parameter values. Additionally, we find that ξ scales as λ4/3 for the entire range of the wavelength λ, regardless of the values of σ2 and lc. We demonstrate that under sufficiently strong disorder, the scaling behavior of the localization length for all other incident angles converges to that for the critical incidence.

Bias-induced circular current in a loop nanojunction with AAH modulation: Role of hopping dimerization

In this work, we investigate the interplay between correlated disorder and hopping dimerization on bias-driven circular current in a loop conductor that is clamped between two electrodes. The correlated disorder is introduced in site energies of the ring in the form of Aubry-André-Harper (AAH) model. Simulating the quantum system within a tight-binding framework all the results are worked out based on the waveguide theory. Unlike transport current, circular current in the loop conductor can get enhanced with increasing disorder strength. This enhancement becomes much effective when hopping dimerization is included which is taken following the Su-Schrieffer-Heeger (SSH) model. The characteristic features of bias-driven circular current are studied under different input conditions and we find that the results are robust for a wide range of physical parameters. For the sake of completeness, uncorrelated disorder is also considered. Our analysis may provide a new insight in analyzing transport behavior in different disordered lattices in the presence of additional restrictions in hopping integrals.

Strong-coupling mean-field and classical percolation approach to produce the phase diagram of disordered Bose–Hubbard model at fixed n = 1 filling

We perform strong-coupling mean-field along with classical percolation analysis to produce the phase diagram of disordered Bose–Hubbard model with chemical potential disorder in two dimensional square lattice. The phase diagram in the disorder strength (Δ) and the on-site repulsion (U), for two and three dimensional system at fixed n = 1 filling show interesting re-entrant superfluid phase sandwiched between Bose-glass phases, as observed by the previous QMC results. We produce the phase diagram exhibiting the re-entrant phenomenon as well as phenomenologically demonstrate the robustness of the re-entrant phenomena within this method. We also discuss the importance of the method and applicability in further analysis of the same phase diagram.

Many-body localization on finite generation fractal lattices

We study many-body localization in a hardcore boson model in the presence of random disorder on finite generation fractal lattices with different Hausdorff dimensions and different local lattice structures. In particular, we consider the Vicsek, T-shaped, Sierpinski gasket, and modified Koch-curve fractal lattices. In the single-particle case, these systems display Anderson localization for arbitrary disorder strength if they are large enough. In the many-body case, the systems available to exact diagonalization exhibit a transition between a delocalized and localized regime, visible in the spectral and entanglement properties of these systems. The position of this transition depends on the Hausdorff dimension of the given fractal, as well as on its local structure.

Super-ballistic diffusion induced by nonlinear interactions in a one-dimensional quasiperiodic lattice

We numerically investigate the spreading dynamics of wave packets in a one-dimensional lattice with quasiperiodic disorders and nonlinear interactions. Under moderate disorder strength, we reveal an intriguing super-ballistic diffusion driven by increasing the interaction strength from the ballistic diffusion in the non- and weakly interacting cases. We obtain a wide parameter region for such a faster-than-ballistic spreading of wave packets in the quasiperiodic lattice, although the nonlinear self-trapping is dominated under strong interactions. The super-ballistic diffusion is further analyzed based on the point source model. We also show the interaction-induced sub-diffusive spreading in the Anderson localized regime. The super-ballistic and sub-diffusive dynamics are exhibited in the spreading that starts from both the single-site and Gaussian wave packets. Our results showcase the interaction-enabled super-ballistic diffusion, which is scarce and experimentally realizable in artificial atomic or photonic lattices.

Weak localization at arbitrary disorder strength in systems with generic spin-dependent fields

Weak localization at arbitrary disorder strength in systems with generic spin-dependent fields

Impact of veteran-led peer mentorship on posttraumatic stress disorder.

Peer mentorship shows promise as a strategy to support veteran mental health. A community-academic partnership involving a veteran-led nonprofit organization and institutions of higher education evaluated a collaboratively developed peer mentor intervention. We assessed posttraumatic stress disorder (PTSD), postdeployment experiences, social functioning, and psychological strengths at baseline, midpoint, and 12-week discharge using the PTSD Checklist for DSM-5 (PCL-5), Deployment Risk and Resilience Inventory-2, Social Adaptation Self-evaluation Scale, and Values in Action Survey. Brief weekly check-in surveys reinforced mentor contact and assessed retention. The sample included 307 veterans who were served by 17 veteran peer mentors. Mixed-effects linear models found a modest effect for PTSD symptom change, with a mean PCL-5 score reduction of 4.04 points, 95% CI [-6.44, -1.64], d = 0.44. More symptomatic veterans showed a larger effect, with average reductions of 9.03 points, 95% CI [-12.11, -5.95], d = 0.77. There were no significant findings for other outcome variables. Compared to younger veterans, those aged 32-57 years were less likely to drop out by 6 weeks, aORs = 0.32-0.26. Week-by-week hazard of drop-out was lower with mentors ≥ 35 years old, aHR = 0.62, 95% CI [0.37, 1.05]. Unadjusted survival differed by mentor military branch, p =.028, but the small mentor sample reduced interpretability. Like many community research efforts, this study lacked a control group, limiting the inferences that can be drawn. Continued study of veteran peer mentorship is important as this modality is often viewed as more tolerable than therapy.

Extracting kinetic information from short-time trajectories: relaxation and disorder of lossy cavity polaritons

Abstract The emerging field of molecular cavity polaritons has stimulated a surge of experimental and theoretical activities and presents a unique opportunity to develop the many-body simulation methodology. This paper presents a numerical scheme for the extraction of key kinetic information of lossy cavity polaritons based on the transfer tensor method (TTM). Steady state, relaxation timescales, and oscillatory phenomena can all be deduced directly from a set of transfer tensors without the need for long-time simulation. Moreover, we generalize TTM to disordered systems by sampling dynamical maps and achieve fast convergence to disordered-averaged dynamics using a small set of realizations. Together, these techniques provide a toolbox for characterizing the interplay of cavity loss, disorder, and cooperativity in polariton relaxation and allow us to predict unusual dependences on the initial excitation state, photon decay rate, strength of disorder, and the type of cavity models. Thus, using the example of cavity polaritons, we have demonstrated significant potential in the use of the TTM toward both the efficient computation of long-time polariton dynamics and the extraction of crucial kinetic information about polariton relaxation from a small set of short-time trajectories.

Phase diagram and crossover phases of topologically ordered graphene zigzag nanoribbons: role of localization effects

We computed the phase diagram of zigzag graphene nanoribbons as a function of on-site repulsion, doping, and disorder strength. The topologically ordered phase undergoes topological phase transitions into crossover phases, which are new disordered phases with non-universal topological entanglement entropy that exhibits significant variance. We explored the nature of non-local correlations in both the topologically ordered and crossover phases. In the presence of localization effects, strong on-site repulsion and/or doping weaken non-local correlations between the opposite zigzag edges of the topologically ordered phase. In one of the crossover phases, both e−/2 solitonic fractional charges and spin-charge separation were absent; however, charge-transfer correlations between the zigzag edges were possible. Another crossover phase contains solitonic e−/2 fractional charges but lacks charge transfer correlations. We also observed properties of non-topological, strongly disordered, and strongly repulsive phases. Each phase on the phase diagram exhibits a different zigzag-edge structure. Additionally, we investigated the tunneling of solitonic fractional charges under an applied voltage between the zigzag edges of undoped topologically ordered zigzag ribbons, and found that it may lead to a zero-bias tunneling anomaly.

Conductivity in the half-filled disordered Hubbard model: A typical medium dynamical mean-field study

The conductivity for half-filled disordered Hubbard model in different interaction regimes is studied using a typical medium dynamical mean-field theory. The Kubo formula with the geometrically averaged Green function is used to calculate the optical and dc conductivity of the system. The dependence of the conductivities in the model on the random potential and temperature in the weak and intermediate interaction regimes is investigated numerically. It is shown that in the weak interaction regime at a fixed temperature the optical conductivity at low frequencies as well as the dc conductivity get decreased as disorder strength increases. Whereas in the intermediate interaction regime, the results show a reentrant effect of the insulating phases. Our dc conductivity of a non-interacting disordered system is consistent with those known in the literature and our other results are in agreement with the phase diagram obtained by using typical medium theory with different impurity solvers.

Enhanced many-body localization in a kinetically constrained model.

In the study of the thermalization of closed quantum systems, the role of kinetic constraints on the temporal dynamics and the eventual thermalization is attracting significant interest. Kinetic constraints typically lead to long-lived metastable states depending on initial conditions. We consider a model of interacting hardcore bosons with an additional kinetic constraint that was originally devised to capture glassy dynamics at high densities. As a main result, we demonstrate that the system is highly prone to localization in the presence of uncorrelated disorder. Adding disorder quickly triggers long-lived dynamics as evidenced in the time evolution of density autocorrelations. Moreover, the kinetic constraint favors localization also in the eigenstates, where a finite-size transition to a many-body localized phase occurs for much lower disorder strengths than for the same model without a kinetic constraint. Our work sheds light on the intricate interplay of kinetic constraints and localization and may provide additional control over many-body localized phases in the time domain.

Disrupted inter-brain synchronization in the prefrontal cortex between adolescents and young adults with gaming disorders during the real-world cooperating video games

BackgroundGaming disorder (GD) and hazardous gaming (HG) have a high incidence among adolescents and young adults and have caused various negative consequences. Interpersonal interaction deficits are closely related to GD and HG, however, the underlying brain mechanisms are still unclear. MethodsThe current study recruited 46 healthy subjects and 32 subjects with GD/HG. Gaming time and frequency, gaming disorder risks, life events, strengths, and difficulties were measured with scales. Subjects were randomly paired into 12 HC-HC dyads, 15 GD/HG-HC dyads, and 7 GD/HG-GD/HG dyads and in pairs completed a real-world cooperating video game — “Tied Together” with functional near-infrared spectroscopy hyperscanning recording in the prefrontal cortex. The inter-brain synchronization in each region of the PFC between dyads was calculated by wavelet to transform coherence to measure brain-to-brain synchronization. ResultsWe found subjects with GD/HG reported higher risks of gaming. The highest IBS in the left dorsolateral prefrontal cortex significantly decreased in the GD/HG-HC and GD/HG-GD/HG dyads compared with healthy controls. A decreasing highest IBS of the left dlPFC was related to a decreasing level of peer problems. LimitationsWe declare limitations of age gaps of samples, undistinguishing GD from HG, use of sub-samples, and the broad concept of interpersonal interaction. ConclusionsThe current study found a decreased highest IBS in the left dlPFC among adolescents and young adults with gaming diseases. It may provide new prevention and treatment insights into gaming disorders targeting disrupted interpersonal interaction.

Design of a Majorana trijunction

Braiding of Majorana states demonstrates their non-Abelian exchange statistics. One implementation of braiding requires control of the pairwise couplings between all Majorana states in a trijunction device. To have adiabaticity, a trijunction device requires the desired pair coupling to be sufficiently large and the undesired couplings to vanish. In this work, we design and simulate a trijunction device in a two-dimensional electron gas with a focus on the normal region that connects three Majorana states. We use an optimisation approach to find the operational regime of the device in a multi-dimensional voltage space. Using the optimization results, we simulate a braiding experiment by adiabatically coupling different pairs of Majorana states without closing the topological gap. We then evaluate the feasibility of braiding in a trijunction device for different shapes and disorder strengths.

Thin film Weyl semimetals with turning number of Fermi surface greater than unity

The development of Weyl semimetals (WSMs) as a new type of quantum material for a variety of novel phenomena is underway. In this context WSM with broken time reversal symmetry and inversion symmetry confined to a thin film which exhibits topologically distinct Fermi surface in the low energy regime is presented. The equi-energy contours possess a topological invariant called turning number ν. We extend the numerical investigation of the magnetotransport in the WSM to include systems with the turning number of Fermi surface greater than unity, ν=2, which is due to the self intersection of equi-energy contours. This results in exotic Weyl orbits which are a hybrid of bulk and surface states and are crucial for magnetotransport. This is in contrast to the conventional electron gas in which orbits are closed curves without self intersection. The contour of Weyl orbits in real space is connected to the shape of Fermi surface. In the presence of a perpendicular magnetic field on a slab geometry, the probability density of edge states are wide and narrow on each edge rather than symmetric on both edges (the hall mark of conventional quantum Hall effect). We explore the effect of disorder on these asymmetric edge states and find that the conductance remains quantized at 2e2/h up to a critical disorder strength. Our findings show that the transport characteristics of WSM are more robust to disorder in a particular direction for these systems with higher turning number. These systems also show unusual conductance by a slanted magnetic field as the slant can modify the Landau levels at the Fermi level.

Work Statistics and Entanglement Across the Fermionic Superfluid‐Insulator Transition

AbstractEntanglement in many‐body systems may display quantum phase transition signatures, and analogous insights are emerging in the study of work fluctuations. Here, the fermionic superfluid‐to‐insulator transition (SIT) is considered and related to its entanglement properties and its work distribution statistics. Using the attractive fermionic Hubbard model with randomly distributed impurities, the work distribution is analyzed under two quench protocols triggering the SIT. In the first, the concentration of impurities is increased; in the second, the impurities' disorder strength is varied. The results indicate that, at criticality, the entanglement is minimized while the average work is maximized. This study demonstrates that, for this state, density fluctuations vanish at all orders, resulting in all central moments of the work probability distribution being precisely zero. For systems undergoing a precursor to the transition (short chains with finite impurity potential) numerical results confirm these predictions, with higher moments further from the ideal results. For both protocols, at criticality, the system absorbs the most energy with almost no penalty in terms of fluctuations: ultimately this feature can be used to implement a quantum critical battery. The impact of temperature on this critical behaviour is also investigated and shown to favor work extraction for high enough temperatures.

Disorder in AdS$_3$/CFT$_2$

We perturbatively study marginally relevant quenched disorder in AdS_33/CFT_22 to second order in the disorder strength. Using the Chern-Simons formulation of AdS_33 gravity for the Poincaré patch, we introduce disorder via the chemical potentials. We discuss the bulk and boundary properties resulting from the disorder-averaged metric. The disorder generates a small mass and angular momentum. In the bulk and the boundary, we find unphysical features due to the disorder average. Motivated by these features, we propose a Poincaré-Lindstedt-inspired resummation method. We discuss how this method enables us to remove all of the unphysical features and compare with other approaches to averaging.

The Impact of Short-Range (Gaussian) Disorder Correlations on Superconducting Characteristics

The pursuit of enhanced superconducting device performance has historically focused on minimizing disorder in materials. Recent research, however, challenges this conventional wisdom by exploring the unique characteristics of disordered materials. Following the studies, disorder is currently viewed as a design parameter that can be tuned. This shift in the paradigm has sparked an upsurge in research efforts, which demonstrates that disorder can significantly augment the superconductivity figures of merit. While almost all previous studies attended to the effects related to disorder strength, this article focuses on the impact of short-range disorder correlations that in real materials takes place, for example, due to lattice defects. The study shows that the degree of such correlations can strongly influence the superconducting characteristics.

Localization transition in non-Hermitian coupled chain

In this paper, we study the properties of a coupled chain modulated by the quasiperiodic complex potential. It is found that as the disorder strength increases, the system undergoes a localization transition from a fully extended phase to an intermediate phase, and then to a fully localized phase. The numerical solving of order parameters such as the average inverse participation ratio and the average normalized participation ratio, demonstrate that the fully extended phase, the intermediate phase with mobility edges, and the fully localized phase are all existent during the transition. The scalar analysis of the normalized participation ratio, confirms the stable existence of three different localization phases in the system. Moreover, the analytical derivation, shows that the localization transition from the extended phase to the intermediate phase and from the intermediate phase to the localized phase can be precisely determined. In addition, the local phase diagram of the system is also obtained by numerical calculation, as shown in Fig. (a). The regions for the extended, intermediate and localized phases are denoted by I-a (I-b), II, and III, respectively. The three black solid lines represent the localization transition points determined by the analytical results. One can see that the analytical results match the numerical results. Moreover, we discuss that the relationship between the real-complex spectrum transition and the localization transition. It is found that the energy spectrum of the system can undergo two real-to-complex transitions. Specifically, during the transition from the fully extended phase to the intermediate phase, the first real-complex transition occurs, where part of the energy spectrum changes from the real spectrum to the complex spectrum, while another part spectrum remains real. When the system transitions from the intermediate phase to the fully localized phase, the energy spectrum completely transforms into a complex spectrum. These research results provide a reference for the study of localization transitions and real-complex transitions in one-dimensional coupled chain systems, and also offer a new perspective for the study of localization.

Metallic–insulator phase transitions in the power-law modulated Harper model

In this work we investigate the transport properties of non-relativistic quantum particles on incommensurate multilayered structures with the thicknesses wn of the layers following a power-law modulated Harper model given by wn=w0|cos(πanν)|. For the normal incidence case, which means an one-dimensional system, we obtained that for a specific range of energy, it is possible to see a metallic–insulator transition with the exponent ν. A metallic phase is supported for ν<1. We also obtained that for the specific value ν=1 there is an alternation between metallic and insulator phases as we change the disorder strength w0. When we integrate out all incidence angles, which means a two-dimensional system, the metallic–insulator transition can be seen for much larger range of energy compared to the normal incidence case.

Information content in continuous attractor neural networks is preserved in the presence of moderate disordered background connectivity.

Continuous attractor neural networks (CANN) form an appealing conceptual model for the storage of information in the brain. However a drawback of CANN is that they require finely tuned interactions. We here study the effect of quenched noise in the interactions on the coding of positional information within CANN. Using the replica method we compute the Fisher information for a network with position-dependent input and recurrent connections composed of a short-range (in space) and a disordered component. We find that the loss in positional information is small for not too large disorder strength, indicating that CANN have a regime in which the advantageous effects of local connectivity on information storage outweigh the detrimental ones. Furthermore, a substantial part of this information can be extracted with a simple linear readout.