arXiv subjects

T. Senthil

Publications and source records attributed to T. Senthil.

At least 19 recordsLinked to original sources

arXiv2026

Fractionalized metals from doped anyons: Application to tMoTe2

A fluid of mobile anyons may arise naturally when a Fractional Quantum Anomalous Hall (FQAH) state is doped. Motivated by recent experiments on twisted $MoTe_2$, we study metallic phases obtained by doping the $\sigma_{xy} = 2e^2/3h$ state. We propose that the high-resistivity metal observed adjacent to this FQAH state is a $Z_3$ Orthogonal Metal: a non-Fermi liquid with sharp charge $1/3$ fermionic quasiparticles coupled to a discrete $Z_3$ gauge field but with no sharp electronic quasiparticle. For a dilute gas of three species of charge-$1/3$ anyons with $\pi/3$ statistics, we construct two $U(3)$ symmetric $Z_3$ Orthogonal Metals, distinguished by whether the gapless fermions transform as $SU(3)$ triplets or singlets. We show that these states naturally yield large electrical resistivities even when the fractionalized quasiparticles are in a good metallic regime. Pairing of the charge-$1/3$ fermions produces an ordinary charge-$2e$ superconductor, smoothly connected to a BCS state but obtained through an intrinsically fractionalized normal state. We discuss experimental signatures of the idea that the normal metallic state in the lightly doped $2/3$ state may have fractionalized charge carriers.

cond-mat.str-el↗

arXiv2026

Superconductivity and non-Fermi liquid metals in a charge-1/3 anyon fluid

We revisit the charge-1/3 anyon fluid obtained by doping the $\nu = 2/3$ Jain fractional Chern insulator (FCI). In the standard composite fermion description, the doped anyons fractionalize into three translation-related flavors of secondary composite fermions, whose gauge-mediated interactions drive a robust inter-flavor pairing instability. In our previous work, we analyzed a flavor-asymmetric paired state and obtained a charge-ordered Fermi liquid. Inspired by a recent paper, we consider an alternative flavor-symmetric paired state and show that it is an SC* state: a charge-$2e$ condensate that coexists with residual $\mathbb{Z}_2$ topological order. The weak and strong pairing regimes share the same intrinsic topological order but differ in chiral central charge, giving $c_- = 7/2$ and $c_- = 2$. We further show how other proposed effective field theories fit within the same composite fermion description, and argue that across the doping driven FCI-to-superconductor transition, localized anyons evolve into Bogoliubov quasiparticles rather than vortices. At low doping, we identify an approximate SU(3)-symmetric regime in which the system instead realizes a non-Fermi liquid $\mathbb{Z}_3$ Orthogonal Metal with three charge-1/3 fermion pockets and no sharp electron quasiparticle. Finally, we comment on the energetics of various possible ground states and discuss implications for experiments in moire materials.

cond-mat.str-el↗

arXiv2026

Measuring anyon dispersion with tunneling probes

Anyons are usually characterized by their topological data and their fractional quantum numbers under global symmetries. In lattice systems such as fractional Chern insulators (FCI), they are also mobile quasiparticles. Their motion controls the possible ground states of the dilute anyon gas obtained by doping an FCI, including possible superconducting states. We show how tunneling probes can measure this motion. In scanning tunneling spectroscopy, weak disorder produces spatially oscillating quasiparticle-interference patterns whose branches reveal the dispersion of fractionalized constituents. In quantum twisting microscopy, planar momentum-conserving tunneling selects the total momentum of the injected electron, so the continuum thresholds of fractionalized electron spectra encode the dispersion of the constituent anyons. The resulting spectra distinguish compact electron-like excitations, bound anyon molecules, and unbound anyon continuum.

cond-mat.mes-hall↗

arXiv2025

Non-Abelian topological superconductivity from melting Abelian fractional Chern insulators

Fractional Chern insulators (FCI) are exotic phases of matter realized at partial filling of a Chern band that host fractionally charged anyon excitations. Recent numerical studies in several microscopic models reveal that increasing the bandwidth in an FCI can drive a direct transition into a charge-2e superconductor rather than a conventional Fermi liquid. Motivated by this surprising observation, we propose a theoretical framework that captures the intertwinement between superconductivity and fractionalization in a lattice setting. Leveraging the duality between three field-theoretic descriptions of the Jain topological order, we find that bandwidth tuning can drive a single parent FCI at $\nu = 2/3$ into five different superconductors, some of which are intrinsically non-Abelian and support Majorana zero modes. Our results reveal a rich landscape of exotic superconductors with no normal state Fermi surface and predict novel higher-charge superconductors coexisting with neutral non-Abelian topological order at more general filling fractions $\nu = p/(2p+1)$.

cond-mat.str-el↗

arXiv2025

Expert Evaluation of LLM World Models: A High-$T_c$ Superconductivity Case Study

Large Language Models (LLMs) show great promise as a powerful tool for scientific literature exploration. However, their effectiveness in providing scientifically accurate and comprehensive answers to complex questions within specialized domains remains an active area of research. Using the field of high-temperature cuprates as an exemplar, we evaluate the ability of LLM systems to understand the literature at the level of an expert. We construct an expert-curated database of 1,726 scientific papers that covers the history of the field, and a set of 67 expert-formulated questions that probe deep understanding of the literature. We then evaluate six different LLM-based systems for answering these questions, including both commercially available closed models and a custom retrieval-augmented generation (RAG) system capable of retrieving images alongside text. Experts then evaluate the answers of these systems against a rubric that assesses balanced perspectives, factual comprehensiveness, succinctness, and evidentiary support. Among the six systems two using RAG on curated literature outperformed existing closed models across key metrics, particularly in providing comprehensive and well-supported answers. We discuss promising aspects of LLM performances as well as critical short-comings of all the models. The set of expert-formulated questions and the rubric will be valuable for assessing expert level performance of LLM based reasoning systems.

cond-mat.supr-con↗

arXiv2025

When Wannier centers jump: Critical points between atomic insulating phases

We study a class of quantum phase transitions between featureless bosonic atomic insulators in $(2+1)$ dimensions, where each phase exhibits neither topological order nor protected edge modes. Despite their lack of topology, these insulators may be ``obstructed'' in the sense that their Wannier centers are not pinned to the physical atomic sites. These insulators represent distinct phases, as no symmetry-preserving adiabatic path connects them. Surprisingly, we find that for certain lattices, the critical point between these insulators can host a conformally invariant state described by quantum electrodynamics in $(2+1)$ dimensions (QED$_3$). The emergent electrodynamics at the critical point can be stabilized if the embedding of the microscopic lattice symmetries suppresses the proliferation of monopoles, suggesting that even transitions between trivial phases can harbor rich and unexpected physics. We analyze the mechanism behind this phenomenon, discuss its stability against perturbations, and explore the embedding of lattice symmetries into the continuum through anomaly matching. In all the models we analyze, we confirm that the QED$_3$ is indeed emergeable, in the sense that it is realizable from a local lattice Hamiltonian.

cond-mat.str-el↗

arXiv2025

Defect mediated quantum melting of charge ordered insulators

Two-dimensional (2d) electronic systems on a lattice at fractional filling $\nu = p/q$ exhibit a competition between charge ordered insulators, called Wigner-Mott insulators (WMIs), at large Coulomb repulsion and Fermi-liquid metals at large electronic kinetic energy. When those two energy scales are roughly equal, insulating states that restore the lattice translation symmetry, which we call quantum charge liquids (QCLs), may emerge. When gapped, these QCLs must exhibit topological order. In this work, we show that the allowed topological ordered phases that are proximate to the WMI strongly depend on the charge ordering in the WMI. In particular, we show that when $q$ is even, no direct transition exists between a WMI with the smallest allowed unit cell size from filling constraints, i.e., the "minimal" WMI, and the topological order with the smallest ground state degeneracy on a torus allowed by filling constraints, i.e., the "minimal" TO. Furthermore, we describe the quantum melting transition of the WMIs to the proximate QCLs in terms of the proliferation of the topological defects of the WMIs. The field theory of this transition in terms of the topological defects reveals their role as precursors to the anyon excitations in the QCLs.

cond-mat.str-el↗

arXiv2025

The Sound of Electrons Shattering: Current Noise Composition Laws for Electron Fractionalization

We develop a theory of the non-equilibrium current response for metallic systems near quantum critical points where electronic quasiparticles fractionalize, such as systems near continuous metal-insulator transitions or composite Fermi liquid to Fermi liquid transitions. Applying a generalized response theory within a Keldysh path integral framework, we derive a non-perturbative current noise composition law, wherein the total noise is the sum of the noise of each fractionalized constituent (bosonic holons and fermionic spinons), weighted by their respective resistivities. We demonstrate that the formally derived composition relations can be interpreted in terms of a simple analogy with resistors in series. We leverage this composition rule near certain quantum critical points to show that the shot noise can be suppressed in long nanowires as compared to Fermi liquid expectations due to the collusion of quantum criticality with fractionalization.

cond-mat.str-el↗

arXiv2025

Pathways from a chiral superconductor to a composite Fermi liquid

Recent experiments have reported chiral time-reversal broken superconductivity in $n$-layer rhombohedral graphene for $n = 4,5, 6$. Introducing a moir\'e potential by alignement with a hexagonal boron nitride substrate suppresses the superconductivity but leads instead to various fractional quantum anomalous Hall phenomena. Motivated by these observations, we consider the fate of the phase transition between (a chiral) Landau Fermi liquid (LFL) metal and a Composite Fermi Liquid (CFL) metal in the presence of attractive interactions. These are parent states, respectively, for the superconductor and the fractional quantum Hall states. For weak attractive interactions, the LFL is usually unstable to superconductivity while the CFL is stable. This raises the possibility of a direct continuous phase transition between the chiral superconductor and the CFL. However, we show that generically the LFL close to the transition to the CFL is stable against superconductivity. Thus the evolution between the CFL and chiral superconductor goes through an intermediate stable LFL phase for weak attractive interactions. With stronger interactions, the evolution can instead go through a non-Abelian paired quantum Hall state.

cond-mat.str-el↗

arXiv2025

Unnecessary quantum criticality in $SU(3)$ kagome magnets

Algebraic/Dirac spin liquids (DSLs) are a class of critical quantum ground states that do not have a quasi-particle description. DSLs and related spin liquid phases often arise in strongly frustrated quantum spin systems, in which strong correlations and quantum fluctuations among constituent spins persist down to zero temperature. In this work, we analyze Mott insulating phases of $SU(3)$ fermions on a kagome lattice which may realize a DSL phase, described at low energies by $(2 + 1)d$ quantum electrodynamics (QED$_3$) with $N_f=6$ Dirac fermions. By analyzing the action of physical symmetries on the operators of the QED$_3$ theory, we conclude that the low energy DSL is a quantum critical point that can be accessed by tuning a single microscopic parameter. Aided by the emergent symmetry and anomalies of the low energy effective theory, we conjecture and present supporting arguments that the $SU(3)$ Kagome magnet DSL is an unnecessary quantum critical point, lying completely within a single phase.

cond-mat.str-el↗

arXiv2025

Emergent QED$_3$ at the bosonic Laughlin state to superfluid transition

Quantum phase transitions between topologically ordered and symmetry-broken phases lie beyond Landau theory. A prime example is the conjectured continuous transition from the bosonic $\nu = 1/2$ Laughlin state to a superfluid, proposed to be governed by a QED$_3$--Chern--Simons (CS) critical point whose stability remains uncertain. We study half-filled bosons in the lowest Landau level subject to a lattice potential. Infinite-cylinder DMRG reveals a single continuous Laughlin--to--superfluid transition. Adiabatic flux insertion collapses the many-body gap and exposes massless Dirac quasiparticles, while momentum-resolved correlation lengths show that three lattice-related density modes share the same critical exponent, evidencing an emergent $SO(3)$ symmetry. The joint appearance of Dirac dispersion and symmetry enlargement provides microscopic support for a stable QED$_3$--CS fixed point. Our numerical strategy also offers a blueprint for exploring Landau-forbidden transitions in fractional Chern insulators and composite Fermi liquids realised in moire and cold-atom systems.

cond-mat.str-el↗

arXiv2025

Anyon delocalization transitions out of a disordered FQAH insulator

Motivated by the experimental discovery of the fractional quantum anomalous Hall (FQAH) effect, we develop a theory of doping-induced transitions out of the $\nu = 2/3$ lattice Jain state in the presence of quenched disorder. We show that disorder strongly affects the evolution into the conducting phases described in our previous work. The delocalization of charge $2/3$ anyons leads to a chiral topological superconductor through a direct second order transition for a smooth random potential with long-wavelength modulations. The longitudinal resistance has a universal peak at the associated quantum critical point. Close to the transition, we show that the superconducting ground state is an ``Anomalous Vortex Glass (AVG)'' stabilized in the absence of an external magnetic field. For short-wavelength disorder, this transition generically splits into three distinct ones with intermediate insulating topological phases. If instead, the charge $1/3$ anyon delocalizes, then at low doping the result is a Reentrant Integer Quantum Hall state with $\rho_{xy} = h/e^2$. At higher doping this undergoes a second transition to a Fermi liquid metal. We show that this framework provides a plausible explanation for the complex phase diagram recently observed in twisted MoTe$_2$ near $\nu = 2/3$ and discuss future experiments that can test our theory in more detail.

cond-mat.str-el↗

arXiv2025

Ordering the topological order in the fractional quantum Hall effect

We discuss the possible topological order/topological quantum field theory of different quantum Hall systems. Given the value of the Hall conductivity, we constrain the global symmetry of the low-energy theory and its anomaly. Specifically, the one-form global symmetry and its anomaly are presented as the organizing principle of these systems. This information is powerful enough to lead to a unique minimal topological order (or a small number of minimal topological orders). Almost all of the known experimentally discovered topological orders are these minimal theories. Since this work is interdisciplinary, we made a special effort to relate to researchers with different backgrounds by providing translations between different perspectives.

cond-mat.str-el↗

arXiv2025

Doping lattice non-abelian quantum Hall states

We study quantum phases of a fluid of mobile charged non-abelian anyons, which arise upon doping the lattice Moore-Read quantum Hall state at lattice filling $\nu = 1/2$ and its generalizations to the Read-Rezayi ($\mathrm{RR}_k$) sequence at $\nu = k/(k+2)$. In contrast to their abelian counterparts, non-abelian anyons present unique challenges due to their non-invertible fusion rules and non-abelian braiding structures. We address these challenges using a Chern-Simons-Ginzburg-Landau (CSGL) framework that incorporates the crucial effect of energy splitting between different anyon fusion channels at nonzero dopant density. For the Moore-Read state, we show that doping the charge $e/4$ non-abelion naturally leads to a fully gapped charge-$2$ superconductor without any coexisting topological order. The chiral central charge of the superconductor depends on details of the interactions determining the splitting of anyon fusion channels. For general $\mathrm{RR}_k$ states, our analysis of states obtained by doping the basic non-abelion $a_0$ with charge $e/(k+2)$ reveals a striking even/odd pattern in the Read-Rezayi index $k$. We develop a general physical picture for anyon-driven superconductivity based on charge-flux unbinding, and show how it relates to the CSGL description of doped abelian quantum Hall states. Finally, as a bonus, we use the CSGL formalism to describe transitions between the $\mathrm{RR}_k$ state and a trivial period-$(k+2)$ CDW insulator at fixed filling, driven by the gap closure of the fundamental non-abelian anyon $a_0$. Notably, for $k=2$, this predicts a period-4 CDW neighboring the Moore-Read state at half-filling, offering a potential explanation of recent numerical observations in models of twisted MoTe$_2$.

cond-mat.str-el↗

arXiv2025

Higgs-mode electromagnon in the spin-spiral multiferroic CuBr${}_2$

Below a continuous symmetry breaking phase transition, the relevant collective excitations are due to longitudinal and transverse fluctuations of the order parameter, which are referred to as Higgs and Goldstone modes, respectively. In solids, these modes may take on a different character than the equivalent excitations in particle physics due to the diverse vacuum states accessible in condensed matter. However, the Higgs mode in particular is quite difficult to observe experimentally as it decays quickly into the lower-energy Goldstone bosons and thus has a negligible lifetime in most systems. In this work, we report evidence for a novel Higgs mode in the multiferroic material CuBr${}_2$, which shows up as a coherent oscillation in the time-resolved second harmonic generation signal upon excitation with a femtosecond light pulse. Since the spiral spin order in CuBr${}_2$ induces a nonzero electric dipole moment in equilibrium, the Higgs mode--which is due to fluctuations in the amplitude of the on-site spin expectation value--is an electromagnon, and thus acquires an inversion quantum number of -1. This is in stark contrast to the Higgs boson of particle physics, which has even parity. Moreover, the excitation described here represents an entirely new type of electromagnon, distinct from the traditional electromagnon in linear spin wave theory which is due to the Goldstone mode.

cond-mat.str-el↗

arXiv2025

Elastic Response and Instabilities of Anomalous Hall Crystals

Anomalous Hall crystals (AHCs) are exotic phases of matter that simultaneously break continuous translation symmetry and exhibit the quantum anomalous Hall effect. AHCs have recently been proposed to explain the observation of an integer quantum anomalous Hall phase in a multilayer graphene system. Despite intense theoretical and experimental interest, little is known about the mechanical properties of AHCs. We study the elastic properties of AHCs first by using a continuum model with quadratic dispersion and uniform Berry curvature. We find using time-dependent Hartree-Fock that the stiffness of the AHC is an order of magnitude smaller than that of the WC, which we attribute to the finite Chern number of the AHC preventing exponential localization of the charge density. By modifying the dispersion relation to include a local minimum modeled after that of rhombohedral pentalayer graphene (R5G), we find that deformations away from the triangular lattice minimize the AHC's kinetic energy, which overwhelms the small stiffness and triggers a mechanical instability. Using a microscopic model of R5G, we observe a similar mechanical instability over an experimentally relevant parameter regime. We conclude that the topologically limited stiffness of AHCs makes them susceptible to mechanical instabilities, an important consideration when interpreting experiments in terms of AHCs.

cond-mat.str-el↗

arXiv2024

Unconventional superconductivity mediated by exciton density wave fluctuations

Synthetic platforms afford an unparalleled degree of controllability in realizing strongly-correlated phases of matter. In this work, we study the possibility of electrically tunable exciton-mediated superconductivity arising in charge-imbalanced bilayer semiconductors. Focusing on the case of a bilayer semiconductor heterostructure, we identify the gating conditions required to achieve exciton density wave order within a self-consistent Hartree-Fock approximation. We analyze the role of the coupling of excitonic fluctuations to the fermionic charge carriers to find that the Goldstone mode of the density wave order can mediate attractive interactions leading to superconductivity. Furthermore, when the system is close to the density wave ordering, the interactions mediated by low-energy exciton modes can support an interlayer pair-density wave superconductor of anisotropic character. We discuss experimental signatures associated with these phenomena.

cond-mat.str-el↗

arXiv2024

Doping a fractional quantum anomalous Hall insulator

We study novel itinerant phases that can be accessed by doping a fractional quantum anomalous Hall (FQAH) insulator, with a focus on the experimentally observed Jain states at lattice filling $\nu = p/(2p+1)$. Unlike in the lowest Landau level, where charge motion is confined into cyclotron orbits, the charged excitations in the FQAH occupy Bloch states with well-defined crystal momenta. At a non-zero doping density, this enables the formation of itinerant states of the doped anyons just beyond the FQAH plateau region. Specializing to the vicinity of $\nu = 2/3$, we describe a few possible such itinerant states. These include a topological superconductor with chiral neutral fermion edge modes as well as a more exotic Pair Density Wave (PDW) superconductor with non-trivial non-Abelian topological order. A Fermi liquid metal with a doping-induced period-3 charge density wave also occurs naturally in our analysis. This Fermi liquid (as well as the PDW) arises from pairing instabilities of a composite Fermi liquid metal that can emerge near filling $2/3$. Though inspired by the theory of anyon superconductivity, we explain how our construction is qualitatively different. At a general Jain filling $\nu = p/(2p+1)$, the same analytical framework leads to a wider variety of phases including higher-charge superconductors and generalized composite Fermi liquids. We predict unusual physical signatures associated with each phase and analyze the crossover between different temperature regimes. These results provide a proof-of-principle that exotic itinerant phases can be stabilized by correlations intrinsic to the FQAH setup.

cond-mat.str-el↗