arXiv subjects

Pavan Hosur

Publications and source records attributed to Pavan Hosur.

At least 19 recordsLinked to original sources

arXiv2026

The Helical SYK Model and Emergent Infrared Integrability

We construct a helical generalization of the Sachdev-Ye-Kitaev (SYK) model in $1+1$ dimensions, built from left- and right-moving Majorana fermions with local quartic interactions and random couplings in flavor-chirality space. These interactions organize into a symmetry-controlled hierarchy of quartic chirality sectors. At the most restrictive end of this hierarchy, symmetry forces the quartic structure into a density-density form, which admits an exact solution using bosonization, rendering the theory integrable. Once the full quartic helical interaction space is allowed, including purely chiral, chirality-balanced, and chirality-imbalanced sectors, this symmetry-protected integrable structure is lost. Nevertheless, the large-$N$ infrared limit remains analytically tractable through short-distance selection rules and disorder averaging. Using conformal perturbation theory about the free fixed point, we show that the entire interaction space is marginally irrelevant, and the theory thus becomes free and integrable in the IR.

hep-th↗

arXiv2026

Eigenstate chaos in the presence of non-Abelian symmetries

The eigenstate thermalization hypothesis (ETH) posits that energy eigenstates encode local properties of the microcanonical ensemble. Motivated by recent interest in the physics of non-commuting conserved charges and the non-Abelian ETH, we study chaotic eigenstates in the presence of symmetries described by general compact Lie groups, such as SU(2). By applying non-Abelian symmetry resolution, we develop a non-Abelian microcanonical entropy and relate this entropy to the entanglement entropy of chaotic eigenstates. We find that microcanonical entropy is closely related to the symmetry-resolved entanglement entropy, which differs from conventional entanglement entropy by a universal logarithmic correction. Our results depend on the global Casimir charge, e.g. total spin. At finite charge density, we find a logarithmic enhancement to conventional entanglement entropy. At zero density, we find no such correction to entanglement entropy, but a logarithmic reduction to microcanonical entropy and symmetry-resolved entanglement entropy. We discuss the implications of our approach for non-Abelian eigenstate thermalization.

quant-ph↗

arXiv2026

Switchable Surface Linear Photogalvanic Effect in the Magnetic Weyl Semimetal Co3Sn2S2

We investigate the linear photogalvanic effect (LPGE) on the surface of the magnetic Weyl semimetal Co3Sn2S2 using a Green's-function and diagrammatic formalism. While the LPGE vanishes in the centrosymmetric bulk, it is symmetry-allowed on the surface where inversion symmetry is broken. We show that unitary crystal symmetries on the surface produce characteristic sign reversals of the total photocurrent at certain polarization angles upon flipping the magnetization. We further find that the intrinsic contribution to the LPGE is strongly constrained by an antiunitary mirror symmetry, which forces several nonlinear response tensor elements to vanish. In contrast, the extrinsic contribution is not subject to these constraints and displays a large magnitude which, we argue, is due to the enhanced density of states associated with Fermi-arc surface states. The current exhibits an approximately linear temperature dependence and a low-frequency power-law scaling, |jy| proportional to omega^-2.2, with weak temperature dependence of the scaling exponent. Our results identify Co3Sn2S2 as a promising platform for experimentally accessing symmetry-controlled nonlinear transport in realistic systems and for applications in magnetically controlled optoelectronic devices.

cond-mat.mes-hall↗

arXiv2026

Chiral vortical effect and boundary-induced vortical pumping in finite Weyl systems

The chiral vortical effect (CVE) -- an axial current driven by rotation in chiral matter -- appears in systems ranging from relativistic fluids to Weyl semimetals. We present an exact quantum solution of a rotating Weyl fermion in a finite cylinder. We recover the exact current density on the rotation axis obtained by Vilenkin and show that its cross-sectional average vanishes in the thermodynamic limit, establishing that the bulk vortical response is purely a magnetization current. For spin-polarized boundary conditions, we uncover an additional effect beyond the known CVE: a robust family of chiral modes that transport axial charge, $\Delta Q=\chi N^2,\Delta\theta/4\pi$, under rotation by angle $\Delta\theta$, where $\chi$ is the Weyl node chirality and $N$ is the number of chiral modes. The pump is independent of temperature, Fermi level, and Weyl velocities, but depends on the UV-sensitive number $N$. These results clarify the quantum structure of the bulk CVE and reveal a boundary-enforced chiral spectral structure underlying vortical response in Weyl systems.

cond-mat.str-el↗

arXiv2026

Pressure-induced Superconductivity in AgSbTe2

AgSbTe2 is a well-known thermoelectric material with a high Seebeck coefficient and intrinsically low thermal conductivity, but its behavior under pressure remains largely unexplored. Here we report a systematic investigation of the structural, electronic, and transport properties of non-stoichiometric AgSbTe2 under high pressure. At ambient pressure, the material can be described as having a cubic crystal structure that remains stable up to 21.7 GPa beyond which it loses long-range structural order, while its crystal system fully recovers upon decompression. Remarkably, superconductivity emerges at a very low pressure of 0.38 GPa with an onset superconducting critical temperature (Tc) of 3.2 K. Tc increases with increasing pressure, reaching 6.9 K at 31.9 GPa, and peaks at 7.4 K during decompression. Magnetic-field-dependent transport measurements and electronic structure calculations reveal an evolution of the superconducting state driven by an enhanced electronic density of states at the Fermi level under compression. Our findings uncover pressure-induced superconductivity in AgSbTe2 and demonstrate that pressure can effectively tune the electronic ground state of thermoelectric materials, extending their functionality beyond thermoelectric energy conversion.

cond-mat.supr-con↗

arXiv2025

Thermodynamic Constraints on Perfect Equilibrium Superconducting Diodes

Superconducting diodes promise dissipationless rectification, yet equilibrium platforms without engineered junctions typically exhibit modest efficiencies. We identify a general thermodynamic origin of this behavior that is largely independent of microscopic details. Denoting $\epsilon = |I_c^-/I_c^+|$, where $I_c^\pm$ are critical currents in opposite directions with $|I_c^+|>|I_c^-|$ by convention, we show that an exact perfect equilibrium diode ($\epsilon=0$) is forbidden by continuity of the free energy. Asymptotically perfect behavior $\epsilon\to0$ is possible within a global equilibrium description, but requires free-energy singularities to enable softening of the unfavorable current-carrying branch. We demonstrate this explicitly in an exactly solvable Ising superconductor model. For smooth single-branch superconductors, standard finite-order polynomial Landau theory yields finite lower bounds on $\epsilon$, while Josephson systems obey analogous bounds set by finite harmonic content of the current-phase relation. The high efficiencies often reported in Josephson platforms arise because such devices commonly operate under phase constraints, metastable switching, or external drive, thereby evading unconstrained equilibrium limits. Thus, our results provide a unified framework for interpreting diode efficiencies across superconducting platforms.

cond-mat.supr-con↗

arXiv2025

Noise-Induced Thermalization in Quantum Systems

In the current Noisy Intermediate-Scale Quantum era, noise is widely regarded as the primary obstacle to achieving fault-tolerant quantum computation. However, certain stages of the quantum computing pipeline can, in fact, benefit from this noise. In this work, we exploit the Eigenstate Thermalization Hypothesis to show that noise generically accelerates a fundamental task in quantum computing -- the preparation of Gibbs states. We demonstrate this behavior using classical and quantum simulations with Haar-random and phase-flip noise, respectively, on a spin-1/2 chain with a local Hamiltonian. Our non-integrable model sees ~3.5x faster thermalization in the presence of noise, while our integrable model, which would not otherwise thermalize, reaches a thermal state due to noise. Since certifying a local Gibbs state is relatively easy on a quantum computer, our approach provides a new practical solution to a key problem in quantum computing. More broadly, these results establish a new paradigm in which noise can be harnessed on quantum computers, enabling practical advantages before the years of fault-tolerance.

quant-ph↗

arXiv2025

Transport scaling and critical tilt effects in disordered two-dimensional Dirac fermions

Two-dimensional (2D) Dirac fermions occur ubiquitously in condensed matter systems from topological phases to quantum critical points. Since the advent of topological semimetals, where the dispersion is often tilted around the band crossing where the Dirac fermion can appear, tilt has emerged as a key handle that controls physical properties. We study how tilt affects the transport and spectral properties of tilted 2D Dirac fermions under scalar disorder. Although our spectral analyses always show conformity to appropriate Gaussian ensembles, suggestive of delocalization, the conductivity scaling $g(L)$ shows a surprising richness. For a single Dirac node, relevant for quantum Hall transitions and topological insulator surface states, we find $g(L)\sim a_1\log(L)$ with a tilt-dependent coefficient $a_1>0$. Interestingly, when the tilt and transport directions are aligned, $a_1$ and hence $g(L)$ shows a spike at the critical point between the type-I and type-II regimes of the Dirac node. For systems with two Dirac nodes with unbroken time-reversal symmetry, pertinent to quasi-2D Dirac materials, we find $g(L)\sim L^{a_1}(\log L)^{a_2}$. However, we find a surprising tension between tilt along and perpendicular to the transport directions. For the former, $a_1$ changes sign as a function of tilt, hinting at a tilt-driven localization-delocalization transition, while $a_1<0$ for all tilts in the latter case, implying localization. These localized behaviors also reveal tension with the delocalization seen in spectral properties and suggest differing localization tendencies in real and Hilbert spaces. Overall, our work identifies tilt as an essential control parameter that uncovers rich and unconventional transport physics in 2D Dirac materials.

cond-mat.dis-nn↗

arXiv2025

Enhanced Superconducting Diode Effect in the Asymmetric Hatsugai-Kohmoto Model

The superconducting diode effect (SDE), characterized by a nonreciprocal supercurrent, has attracted significant attention in recent years due to its potential applications. However, most studies have focused on weakly correlated models, leaving the impact of strong electron-electron interactions on the SDE largely unexplored. In this work, we bridge this gap by investigating the SDE in asymmetric band metals with Hatsugai-Kohmoto (HK) interaction, which are exactly solvable due to their locality in Bloch momentum space. Through a combination of low-energy analysis and a numerical self-consistent approach, we demonstrate that HK interaction can enhance the SDE's quality factor. Our findings shed light on the role of strong electron-electron correlations in shaping the SDE.

cond-mat.supr-con↗

arXiv2025

Kramers nodal lines in intercalated TaS$_2$ superconductors

Kramers degeneracy is one fundamental embodiment of the quantum mechanical nature of particles with half-integer spin under time reversal symmetry. Under the chiral and noncentrosymmetric achiral crystalline symmetries, Kramers degeneracy emerges respectively as topological quasiparticles of Weyl fermions and Kramers nodal lines (KNLs), anchoring the Berry phase-related physics of electrons. However, an experimental demonstration for ideal KNLs well isolated at the Fermi level is lacking. Here, we establish a class of noncentrosymmetric achiral intercalated transition metal dichalcogenide superconductors with large Ising-type spin-orbit coupling, represented by In$_x$TaS$_2$, to host an ideal KNL phase. We provide evidence from angle-resolved photoemission spectroscopy with spin resolution, angle-dependent quantum oscillation measurements, and ab-initio calculations. Our work not only provides a realistic platform for realizing and tuning KNLs in layered materials, but also paves the way for exploring the interplay between KNLs and superconductivity, as well as applications pertaining to spintronics, valleytronics, and nonlinear transport.

cond-mat.supr-con↗

arXiv2025

The Effect of the Non-Abelian Quantum Metric on Superfluidity

The quantum geometric tensor, which encodes the full geometric information of quantum states in projective Hilbert space, plays a crucial role in condensed matter physics. In this work, we examine the effect of the non-Abelian quantum metric -- the real part of the non-Abelian quantum geometric tensor -- on the superfluid weight in time-reversal symmetric systems. For conventional $s$-wave pairing, we demonstrate that the superfluid weight includes a contribution proportional to the trace of the non-Abelian quantum metric. Notably, this contribution remains significant even when the total Chern number of a set of degenerate bands is zero and can exceed the conventional contribution, as confirmed using lattice models. Ab initio density functional theory (DFT) calculations for MoS$_2$ and TiSe$_2$ further corroborate these findings, revealing that the non-Abelian quantum metric accounts for up to 20% of the superfluid weight in MoS$_2$ and 50% in TiSe$_2$. Our results provide new insights into the nontrivial relationship between the geometric properties of quantum states and superconductivity, opening avenues for further exploration in topological and superconducting materials.

cond-mat.supr-con↗

arXiv2024

Digital logic from high-efficiency superconducting diodes

Recent advancements in the realizations of superconducting diodes have pushed the diode coefficient $\eta$ towards its theoretical maximum of $\eta=1$. In this work, we describe the construction of logic gates NOT, AND, OR, NAND and NOR using superconducting diodes with $\eta\approx1$ by exploiting their dynamically tunable polarity. We then argue that fundamental theorems suppress $\eta$ in intrinsic superconductors, rendering them likely unsuitable for the proposed devices, and point out that several previous proposals and platforms, remarkably, bypassed this suppression unwittingly. We discuss the realization of the digital logic in one such platform -- Josephson triodes that yielded $\eta\approx1$ -- and argue that phases with spontaneous spatial or magnetic order can overcome some of its drawbacks. Thus, this work provides guiding principles for future platforms and develops the building blocks for superconductors-based digital electronics.

cond-mat.supr-con↗

arXiv2024

Anomalous Shiba spectrum and superconductivity induced magnetic interactions in materials with topological band inversion

We study the Yu-Shiba-Rusinov states in materials with bulk band inversion such as iron-based topological superconductors or doped topological insulators. We show that the structure of the YSR state spectrum depends on the doping level relative to the chemical potential at which the band-inversion occurs. Moreover, we demonstrate that the transition from ferromagnetic to antiferromagnetic coupling and vice versa, which is caused by the coupling of magnetic impurities through the overlap of YSR states, is highly dependent on the doping level. Additionally, topological edge states may have a substantial impact on the YSR states, leading to a decrease in YSR state energies and the creation of new states when the magnetic impurity approaches the boundary.

cond-mat.supr-con↗

arXiv2024

Robust boundary Luttinger surfaces in topological band structures

The standard paradigm of topological phases posits that two phases with identical symmetries are separated by a bulk phase transition, while symmetry breaking provides a path in parameter space that allows adiabatic connection between the phases. Typically, if symmetry is broken only at the boundary, topological surface states become gapped, and single-particle surface properties no longer distinguish between the two phases. In this work, we challenge this expectation. We demonstrate that the single-particle surface Green's function contains zeros, or "Luttinger surfaces," which maintain the same bulk-boundary correspondence as topological surface states. Remarkably, these Luttinger surfaces persist under symmetry-breaking perturbations that destroy the surface states. Moreover, we point out that low-energy and surface theories, often used synonymously in discussions of (gapped) topological matter, are actually different, with the difference captured by the Luttinger surfaces.

cond-mat.str-el↗

arXiv2024

Nonlinear Hall Effects induced by Berry Curvature Dipole in CuPb$_9$(PO$_4$)$_6$O

The nonlinear Hall effect (NLHE), an emergent response in systems with broken inversion symmetry, provides a powerful tool for probing topological transport properties. In this context, we investigate copper-substituted lead apatite (LK-99), a material that initially garnered attention for its controversial claim of room-temperature superconductivity. Despite the unresolved nature of its superconducting properties, LK-99's unique electronic structure characterized by flat bands near the Fermi level and broken inversion symmetry makes it a promising candidate for exploring Berry curvature-driven phenomena, such as the NLHE. Using first-principles density functional theory and an augmented tight-binding Hamiltonian model, we investigate LK-99's band topology and transport properties. Our calculations indicate that spin-orbit coupling in LK-99 generates multiple Weyl points near the Fermi level, thereby enhancing the Berry curvature distribution by further splitting the bands. Crucially, the absence of inversion symmetry in LK-99 leads to a net Berry curvature dipole, producing a nonlinear Hall current that scales quadratically with the applied electric field. The nonlinear Hall effect is solely due to the BCD, as the contributions from the Drude weight and quantum metric are zero due to time reversal symmetry. Moreover, we demonstrate that the NLHE in LK-99 can be tuned by varying the direction of the applied electric field, underscoring its potential as a versatile platform for exploring topological transport phenomena and designing next-generation nonlinear electronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Generalized Free Cumulants for Quantum Chaotic Systems

The eigenstate thermalization hypothesis (ETH) is the leading conjecture for the emergence of statistical mechanics in generic isolated quantum systems and is formulated in terms of the matrix elements of operators. An analog known as the ergodic bipartition (EB) describes entanglement and locality and is formulated in terms of the components of eigenstates. In this paper, we significantly generalize the EB and unify it with the ETH, extending the EB to study higher correlations and systems out of equilibrium. Our main result is a diagrammatic formalism that computes arbitrary correlations between eigenstates and operators based on a recently uncovered connection between the ETH and free probability theory. We refer to the connected components of our diagrams as generalized free cumulants. We apply our formalism in several ways. First, we focus on chaotic eigenstates and establish the so-called subsystem ETH and the Page curve as consequences of our construction. We also improve known calculations for thermal reduced density matrices and comment on an inherently free probabilistic aspect of the replica approach to entanglement entropy previously noticed in a calculation for the Page curve of an evaporating black hole. Next, we turn to chaotic quantum dynamics and demonstrate the ETH as a sufficient mechanism for thermalization, in general. In particular, we show that reduced density matrices relax to their equilibrium form and that systems obey the Page curve at late times. We also demonstrate that the different phases of entanglement growth are encoded in higher correlations of the EB. Lastly, we examine the chaotic structure of eigenstates and operators together and reveal previously overlooked correlations between them. Crucially, these correlations encode butterfly velocities, a well-known dynamical property of interacting quantum systems.

cond-mat.stat-mech↗

arXiv2023

Intrinsic superconducting diode effects in tilted Weyl and Dirac semimetals

We explore Weyl and Dirac semimetals with tilted nodes as platforms for realizing an intrinsic superconducting diode effect. Although tilting breaks sufficient spatial and time-reversal symmetries, we prove that -- at least for conventional $s$-wave singlet pairing -- the effect is forbidden by an emergent particle-hole symmetry at low energies if the Fermi level is tuned to the nodes. Then, as a stepping stone to the three-dimensional semimetals, we analyze a minimal one-dimensional model with a tilted helical node using Ginzburg-Landau theory. While one might naively expect a drastic enhancement of the effect when the node turns from type-I to type-II, we find that the presence of multiple Fermi pockets is more important as it enables multiple pairing amplitudes with indepedent contributions to supercurrents in opposite directions. Equipped with this insight, we construct minimal lattice models of Weyl and Dirac semimetals and study the superconducting diode effect in them. Once again, we see a substantial enhancement when the normal state has multiple Fermi pockets per node that can accommodate more than one pairing channel. In summary, this study sheds light on the key factors governing the intrinsic superconducting diode effect in systems with asymmetric band structures and paves the way for realizing it in topological semimetals.

cond-mat.supr-con↗

arXiv2023

Chiral kinematic theory and converse vortical effects

Response theories in condensed matter typically describe the response of an electron fluid to external electromagnetic fields, while perturbations on neutral particles are often designed to mimic such fields. Here, we study the response of fermions to a space-time-dependent velocity field, thereby sidestepping the issue of gauge charge. First, we use a semiclassical chiral kinematic theory to obtain the local density of current and extract the orbital magnetization. The theory immediately predicts a "converse vortical effect," defined as an orbital magnetization driven by linear velocity. It receives contributions from magnetic moments on the Fermi surface and the Berry curvature of the occupied bands. Then, transcending semiclassics via a complementary Kubo formalism reveals that the uniform limit of a clean system receives only the Berry curvature contribution while other limits sense the Fermi surface magnetic moments too. We propose CoSi as a candidate material and suggest magnetometry of a sample under a thermal gradient to detect the effect. Overall, our study sheds light on the effects of a space-time-dependent velocity field on electron fluids and paves the way for exploring quantum materials using new probes and perturbations.

cond-mat.other↗