arXiv subjects

Antonio Štrkalj

Publications and source records attributed to Antonio Štrkalj.

14 recordsLinked to original sources

arXiv2026

Thermal avalanches in a quasiperiodic XXZ model

We study bath-induced thermalization in the many-body localized XXZ spin chain subjected to a quasiperiodic magnetic field. We engineer a thermal inclusion by setting the field strength in one part of the chain below the localization threshold and analyze thermalization via the avalanche mechanism. To study the nature of such avalanches, we use two complementary observables, namely the two-point connected correlation function and the particle-number entropy. Surprisingly, the correlations alone show no signatures of avalanches. Instead, they display a logarithmic growth of the correlation length throughout the dynamics and predict localization lengths of the local integrals of motion that remain well below the avalanche threshold. In contrast, the particle number entropy shows clear signatures of the thermal avalanche, with the avalanche front progressively propagating deeper into the localized subsystem for sufficiently large baths. The discrepancy between the two observables shows that two-point correlations are unreliable in identifying thermal avalanches in quasiperiodic systems, as opposed to the random case. On one hand, qualitative results are consistent with the analytical predictions of the standard avalanche theory. On the other hand, significant quantitative deviations persist, which could be due to short-range resonances generated by the quasiperiodic potential. Our results suggest that the standard avalanche framework requires revision to account for the short-range correlations of quasiperiodic potentials.

cond-mat.dis-nn↗

arXiv2026

Quantum Beats in Many-Body Localized Systems

Slow particle dynamics observed numerically even deep inside the many-body localized (MBL) regime has called the stability of MBL in the thermodynamic limit into question, and its microscopic origin remains unknown. Here, we show that this slow dynamics originates from many-body quantum beats that arise from the interaction-induced modulation of oscillations associated with single-particle hopping processes. We relate this mechanism to local integrals of motion (LIOMs) and show that it survives at arbitrarily large distances between LIOMs, is consistent with the stability of MBL in the thermodynamic limit, and is generic to many-body systems. We present new numerical results for quasiperiodic potentials and, based on the quantum beats mechanism, develop an analytical model that explains number entropy growth and quasiparticle spreading, as well as clarifies the distinct MBL phenomenology observed in quasiperiodic and random potentials. Lastly, we propose concrete signatures for observing many-body quantum beats in existing experimental platforms.

cond-mat.dis-nn↗

arXiv2026

Localization and topological signatures under periodic twisting

We theoretically explore a dynamical generalization of the Aubry-André model in two dimensions formed by superimposing two square-lattice potentials. Motivated by the rich physics emerging at different twist angles between the two lattices at equilibrium, we introduce periodic twisting by continuously rotating one of the lattices with respect to the other in the plane. We demonstrate that the distinct time-dependent twisting in this system gives rise to an intricate form of periodic multi-frequency driving that changes with the distance from the rotation axis. We find that the incommensurate nature of the potential no longer plays the pivotal role as it does in the static case. Rather, the tunneling can be understood in terms of a local, spatially varying dynamical localization effect, which we show to yield ring-shaped states localized within the bulk that have interesting transport signatures. Quantifying the eigenstates with the Bott index and local Chern marker, we find that there is a zoo of states with non-trivial topological signatures, the most ubiquitous of which result in relatively uniform ring-shaped regions of the Chern marker. We investigate the origin of these effects from various angles and identify that hybridization between different delocalized ring states plays a vital role. Lastly, we discuss possible experimental realizations in quantum simulation settings. Our results open a new avenue of investigation with periodic twisting inducing a spatially varying multi-frequency drive.

cond-mat.quant-gas↗

arXiv2025

A resonant valence bond spin liquid in the dilute limit of doped frustrated Mott insulators

Ideas about resonant valence bond liquids and spin-charge separation have led to key concepts in physics such as quantum spin liquids, emergent gauge symmetries, topological order, and fractionalisation. Despite extensive efforts to demonstrate the existence of a resonant valence bond phase in the Hubbard model that originally motivated the concept, a definitive realisation has yet to be achieved. Here we present a solution to this long-standing problem by uncovering a resonant valence bond phase exhibiting spin-charge separation in realistic Hamiltonians. We show analytically that this ground state emerges in the dilute-doping limit of a half-filled Mott insulator on corner-sharing tetrahedral lattices with frustrated hopping, in the absence of exchange interactions. We confirm numerically that the results extend to finite exchange interactions, finite-sized systems and finite dopant density. Although much attention has been devoted to the emergence of unconventional states from geometrically frustrated interactions, our work demonstrates that kinetic energy frustration in doped Mott insulators may be essential for stabilising robust, topologically ordered states in real materials.

cond-mat.str-el↗

arXiv2024

Aharonov-Bohm interferometer in inverted-band pn junctions

Inverted-band $pn$ junctions in two-dimensional materials offer a promising platform for electron optics in condensed matter, as they allow to manipulate and guide electron beams without the need for spatial confinement. In this work, we propose the realization of an Aharonov-Bohm (AB) interferometer using such $pn$ junctions. We observe AB oscillations in numerically obtained conductance and analytically identify the conditions for their appearance by analyzing the scattering processes at the $pn$ interface. To support experimental implementation, we also consider junctions with a graded interface, where the potential varies smoothly between the $p$- and $n$-doped regions. Our results reveal an abrupt change in the AB-oscillation frequency, which we attribute to a distinct transition in the hybridization across the interface. We verify that our reported AB oscillations are robust to realistic disorder and temperature decoherence channels. Our study paves the way for realizing the Aharonov-Bohm effect in bulk mesoscopic systems without the need for external spatial confinement, offering new possibilities in electron optics.

cond-mat.mes-hall↗

arXiv2024

Reentrant localisation transitions and anomalous spectral properties in off-diagonal quasiperiodic systems

We investigate the localisation properties of quasiperiodic tight-binding chains with hopping terms modulated by the interpolating Aubry-André-Fibonacci (IAAF) function. This off-diagonal IAAF model allows for a smooth and controllable interpolation between two paradigmatic quasiperiodic models: the Aubry-André and the Fibonacci model. Our analysis shows that the spectrum of this model can be divided into three principal bands, namely, two molecular bands at the edge of the spectrum and one atomic band in the middle, for all values of the interpolating parameter. We reveal that the states in the molecular bands undergo multiple re-entrant localisation transitions, a behaviour previously reported in the diagonal IAAF model. We link the emergence of these reentrant phenomena to symmetry points of the quasiperiodic modulation and, with that, explain the main ground state properties of the system. The atomic states in the middle band show no traces of localised phases and remain either extended or critical for any value of the interpolating parameter. Using a renormalisation group approach, adapted from the Fibonacci model, we explain the extended nature of the middle band. These findings expand our knowledge of phase transitions within quasiperiodic systems and highlight the interplay between extended, critical, and localised states.

cond-mat.dis-nn↗

arXiv2024

Tomasch Oscillations as Above-Gap Signature of Topological Superconductivity

The identification of topological superconductors usually involves searching for in-gap modes that are protected by topology. However, in the current experimental settings, the smoking-gun evidence of these in-gap modes is still lacking. In this work, we propose to distinguish between two-dimensional conventional s-wave and topological p-wave superconductors by above-gap transport signatures. Our method utilizes the emergence of Tomasch oscillations of quasiparticles in a junction consisting of a superconductor sandwiched between two metallic leads. We demonstrate that the behavior of the oscillations in conductance as a function of the interface barriers provides a distinctive signature for s-wave and p-wave superconductors. Specifically, the oscillations become weaker as the barrier strength increases in s-wave superconductors, while they become more pronounced in p-wave superconductors, which we prove to be a direct manifestation of the pairing symmetries. Our method opens a new route for identifying topological superconductors through above-gap transport.

cond-mat.supr-con↗

arXiv2024

Electron-optics using negative refraction in two-dimensional inverted-band $pn$ junctions

Electron optics deals with condensed matter platforms for manipulating and guiding electron beams with high efficiency and robustness. Common devices rely on the spatial confinement of the electrons into one-dimensional channels. Recently, there is growing interest in electron optics applications in two dimensions, which heretofore are almost exclusively based on graphene devices. In this work, we study band-inverted systems resulting from particle-hole hybridization and demonstrate their potential for electron optics applications. We develop the theory of interface scattering in an inverted-band $pn$ junction using a scattering matrix formalism and observe negative refraction conditions as well as transmission filtering akin to graphene's Klein tunneling but at finite angles. Based on these findings, we provide a comprehensive protocol for constructing electron optic components, such as focusing and bifurcating lenses, polarizers, and mirrors. We numerically test the robustness of our designs to disorder and finite temperatures, and motivate the feasibility of experimental realization. Our work opens avenues for electron optics in two dimensions beyond graphene-based devices, where a plethora of inverted-band materials in contemporary experiments can be harnessed.

cond-mat.mes-hall↗

arXiv2023

Emergence of quasiperiodic behavior in transport and hybridization properties of clean lattice systems

Quasiperiodic behaviour is known to occur in systems with enforced quasiperiodicity or randomness, in either the lattice structure or the potential, as well as in periodically driven systems. Here, we present instead a setting where quasiperiodic behaviour emerges in clean, non-driven lattice systems. We illustrate this through two examples of experimental relevance, namely an infinite tight-binding chain with a gated segment, and a hopping particle coupled to static Ising degrees of freedom. We show how the quasiperiodic behaviour manifests in the number of states that are localised by the geometry of the system, with corresponding effects on transport and hybridisation properties.

cond-mat.mes-hall↗

arXiv2022

Coexistence of localization and transport in many-body two-dimensional Aubry-André models

Whether disordered and quasiperiodic many-body quantum systems host a long-lived localized phase in the thermodynamic limit has been the subject of intense recent debate. While in one dimension substantial evidence for the existence of such a many-body localized (MBL) phase exists, the behavior in higher dimensions remains an open puzzle. In two-dimensional disordered systems, for instance, it has been argued that rare regions may lead to thermalization of the whole system through a mechanism dubbed the avalanche instability. In quasiperiodic systems, rare regions are altogether absent and the fate of a putative many-body localized phase has hitherto remained largely unexplored. In this work, we investigate the localization properties of two many-body quasiperiodic models, which are two-dimensional generalizations of the Aubry-André model. By studying the out-of-equilibrium dynamics of large systems, we find a long-lived MBL phase, in contrast to random systems. Furthermore, we show that deterministic lines of weak potential, which appear in investigated quasiperiodic models, support large-scale transport, while the system as a whole does not thermalize. Our results demonstrate that quasiperiodic many-body systems have the remarkable and counter-intuitive capability of exhibiting coexisting localization and transport properties - a phenomenon reminiscent of the behavior of supersolids. Our findings are of direct experimental relevance and can be tested, for instance, using state-of-the-art cold atomic systems.

cond-mat.dis-nn↗

arXiv2021

Many-body localization in the interpolating Aubry-André-Fibonacci model

We investigate the localization properties of a spin chain with an antiferromagnetic nearest-neighbour coupling, subject to an external quasiperiodic on-site magnetic field. The quasiperiodic modulation interpolates between two paradigmatic models, namely the Aubry-André and the Fibonacci models. We find that stronger many-body interactions extend the ergodic phase in the former, whereas they shrink it in the latter. Furthermore, the many-body localization transition points at the two limits of the interpolation appear to be continuously connected along the deformation. As a result, the position of the many-body localization transition depends on the interaction strength for an intermediate degree of deformation of the quasiperiodic modulation. Moreover, in the region of parameter space where the single-particle spectrum contains both localized and extended states, many-body interactions induce an anomalous effect: weak interactions localize the system, whereas stronger interactions enhance ergodicity. We map the model's localization phase diagram using the decay of the quenched spin imbalance in relatively long chains. This is accomplished employing a time-dependent variational approach applied to a matrix product state decomposition of the many-body state. Our model serves as a rich playground for testing many-body localization under tunable potentials.

cond-mat.dis-nn↗

arXiv2021

A Luttinger Liquid coupled to Ohmic-class environments

We investigate the impact of an Ohmic-class environment on the conduction and correlation properties of one-dimensional interacting systems. Interestingly, we reveal that inter-particle interactions can be engineered by the environment's noise statistics. Introducing a backscattering impurity to the system, we address Kane-Fisher's metal-to-insulator quantum phase transition in this noisy and realistic setting. Within a perturbative renormalization group approach, we show that the Ohmic environments keep the phase transition intact, while sub- and super-Ohmic environments, modify it into a smooth crossover at a scale that depends on the interaction strength within the wire. The system still undergoes a metal-to-insulator-like transition when moving from sub-Ohmic to super-Ohmic environment noise. We cover a broad range of realistic experimental conditions, by exploring the impact of a finite wire length and temperature on transport through the system.

cond-mat.str-el↗

arXiv2019

Electron-Hole Interference in an Inverted-Band Semiconductor Bilayer

Electron optics in the solid state promises new functionality in electronics through the possibility of realizing micrometer-sized interferometers, lenses, collimators and beam splitters that manipulate electrons instead of light. Until now, however, such functionality has been demonstrated exclusively in one-dimensional devices, such as in nanotubes, and in graphene-based devices operating with p-n junctions. In this work, we describe a novel mechanism for realizing electron optics in two dimensions. By studying a two-dimensional Fabry-Pérot interferometer based on a resonant cavity formed in an InAs/GaSb double quantum well using p-n junctions, we establish that electron-hole hybridization in band-inverted systems can facilitate coherent interference. With this discovery, we expand the field of electron optics to encompass materials that exhibit band inversion and hybridization, with the promise to surpass the performance of current state-of-the-art devices.

cond-mat.mes-hall↗

arXiv2018

Tunneling into a finite Luttinger liquid coupled to noisy capacitive leads

Tunneling spectroscopy of one-dimensional interacting wires can be profoundly sensitive to the boundary conditions of the wire. Here, we analyze the tunneling spectroscopy of a wire coupled to capacitive metallic leads. Strikingly, with increasing many-body interactions in the wire, the impact of the boundary noise becomes more prominent. This interplay allows for a smooth crossover from standard 1D tunneling signatures into a regime where the tunneling is dominated by the fluctuations at the leads. This regime is characterized by elevated zero-bias tunneling alongside a universal power-law decay at high energies. Furthermore, local tunneling measurements in this regime show a unique spatial-dependence that marks the formation of plasmonic standing waves in the wire. Our result offers a tunable method by which to control the boundary effects and measure the interaction strength (Luttinger parameter) within the wire.

cond-mat.mes-hall↗