arXiv subjects

Ilya Esterlis

Publications and source records attributed to Ilya Esterlis.

At least 19 recordsLinked to original sources

arXiv2026

Wigner polarons reveal Wigner crystal dynamics in a monolayer semiconductor

Wigner crystals, lattices made purely of electrons, are a quintessential paradigm of studying correlation-driven quantum phase transitions. Despite decades of research, the internal dynamics of Wigner crystals has remained extremely challenging to access, with most experiments probing only static order or collective motion. Here, we establish monolayer WSe2 as a new materials platform to host zero-field Wigner crystals and then demonstrate that exciton spectroscopy provides a direct means to probe both static and dynamic properties of these electron lattices. We uncover striking optical resonances that we identify as Wigner polarons, quasiparticles formed when the electron lattice is locally distorted by exciton-Wigner crystal coupling. We further achieve all-optical control of spins in the Wigner crystal, directly probing valley-dependent Wigner polaron scattering well above the magnetic ordering temperature and in the absence of any external magnetic field. Finally, we demonstrate optical melting of the Wigner crystal and observe intriguingly different responses of the umklapp (static) and Wigner polaron (dynamic) resonances to optical excitation. Our results open up exciting new avenues for elucidating electron dynamics and achieving ultrafast optical control of interaction-driven quantum phase transitions in strongly correlated electron systems.

cond-mat.mes-hall↗

arXiv2026

Probing nonlocal superconducting fluctuations with covariance noise magnetometry

The nonlocal superconducting fluctuation corrections to the conductivity tensor $σ_{ij}(\mathbf{q},ω)$ are calculated within the time-dependent Ginzburg-Landau framework, and their observable consequences for quantum noise magnetometry are worked out. For a single nitrogen-vacancy (NV) sensor we obtain the relaxation rate $1/T_1$ as a function of temperature, sample-sensor distance, and probe frequency, identifying the scales at which the nonlocality and the dynamics of the pair fluctuations cut off the critical enhancement near $T_c$. For two-sensor covariance magnetometry we show that the two-point field correlator develops additional spatial structure whose range directly measures the fluctuation correlation length $ξ(T)$. We further analyze two channels that accompany the paraconductivity: the Maki-Thompson correction to the spin susceptibility, and the fluctuation diamagnetism. Finally, we solve exactly, to all orders in a dc electric field and at all wave vectors, for the nonequilibrium current noise of the fluctuating film: the noise decouples from the nonlinear paraconductivity, violating the fluctuation-dissipation theorem by universal factors at criticality and acquiring a bias-induced spatial anisotropy directly measurable by covariance magnetometry. The results are connected to a recent experiment measuring current noise near a thin film of BSCCO.

cond-mat.supr-con↗

arXiv2026

Optical signatures of antiferromagnetic correlations in a strongly interacting quantum Hall MoSe2 monolayer

Strong magnetic fields quench the kinetic energy of electrons, leading to the formation of flat energy bands, known as Landau levels (LLs). In this situation, even weak interactions can drive the emergence of various ordered phases. The simplest of such phases is a quantum Hall ferromagnet, where a spontaneous spin polarization emerges when LLs with opposite spins cross. The presence of strong electron-electron interaction at zero field changes this picture and makes the resulting states much harder to predict. Here we use magneto-optical spectroscopy to reveal quantum Hall states with unconventional correlations favouring an unpolarized state in the strongly correlated electron liquid in a MoSe2 monolayer. The oscillations of the exciton polaron energies as a function of perpendicular magnetic field and electron density demonstrate the emergence of LLs in a correlated electron liquid and density-dependent crossings between LLs of opposite valleys. On lowering the LL filling factor, where interactions within LLs are stronger, the crossings systematically broaden, indicating an increase in the Zeeman energy required to fully polarize the valley-degenerate LLs. These observations are shown to be consistent with antiferromagnetic interactions between LL electrons, favouring a ground state with zero valley polarization, and are therefore inconsistent with conventional quantum Hall ferromagnetism. This discovery demonstrates a qualitatively distinct form of quantum Hall magnetism in a strongly correlated electron liquid, establishing an anchoring point for understanding spin-unpolarized fractional and ordered states of correlated electrons driven by magnetic field.

cond-mat.mes-hall↗

arXiv2026

Limits of validity for Migdal-Eliashberg theory: role of polarons/bi-polarons

It is widely believed that in an adiabatic limit a Fermi liquid state of an electron-phonon system described by Migdal-Eliashberg theory remains stable before a dressed phonon softens. Using Holstein model as a prototypical example and variational/analytic considerations we demonstrate that in a wide range of fillings both in 3D and 2D, a polaronic/bi-polaronic state emerges before phonon softening; at small filling in 3D this happens already at weak coupling. We show that a polaronic/bi-polaronic state emerges, upon increasing coupling, via an intermediate pseudogap-type mixed state, in which some fermions regain Fermi liquid behavior, yet Luttinger theorem is broken. At even larger couplings the density of states gradually approaches its form in the atomic limit.

cond-mat.str-el↗

arXiv2026

Breakdown of the Migdal-Eliashberg theory for electron-phonon systems. Role of polarons/bi-polarons

The Migdal-Eliashberg theory (MET) describes electrons interacting with phonons in the adiabatic limit when the phonon Debye frequency is much smaller than the Fermi energy. A conventional belief is that MET holds even at strong coupling, when electron self-energy is large, and breaks down only near the point where the dressed phonon spectrum softens to near zero. We analyze numerically and analytically a different option -- collapse to a polaronic/bipolaronic ground state. The last scenario has never been analyzed in precise quantitative terms for a generic electron density. Using variational considerations, we establish rigorous upper bounds on the coupling $λ$, at which a FL state transforms into the bipolaron/polaron state. We show that at small and near-maximum densities, this happens well before a dressed phonon softens. This is true both in 2D and 3D systems; in the latter the upper bound on $λ$ tends to zero in the limit of small or near-full density. We present analytical reasoning for this behavior based on hints extracted from exact diagrammatic treatment of the on-site Holstein model for the spin polarized case and argue that polarons are produced by fermions with energies comparable to the bandwidth; i.e., polaron formation is outside the realm of MET. Closer to half-filling, the leading instability upon increasing $λ$ is towards a charge-density-wave state (CDW), and there exists a strong coupling regime of MET near this instability, while the polaron/bipolaron state develops at larger $λ$ out of a CDW-ordered state and inherits a CDW order over some range of coupling.

cond-mat.str-el↗

arXiv2026

Superconductivity near two-dimensional Van Hove singularities: a determinant quantum Monte Carlo study

The superconducting transition temperature $T_c$ of the two-dimensional attractive Hubbard model is computed in the vicinity of both ordinary (logarithmic) and higher-order (power-law) Van Hove singularities using determinant quantum Monte Carlo simulations. For interaction strengths $|U| \lesssim W/3$, where $W$ is the electronic bandwidth, $T_c$ is enhanced in the neighborhood of the Van Hove point, albeit more weakly than expected from weak-coupling BCS theory. Enhancing the Van Hove singularity from logarithmic to power-law yields only a minor additional enhancement of $T_c$. For $|U| \gtrsim W/3$, the maximum $T_c$ shifts away from the Van Hove point and instead occurs at a density unrelated to any features in the non-interacting density of states, consistent with a strong-coupling interpretation. We find that the maximal $T_c$ in the model is achieved at intermediate $U$ and at a density away from the Van Hove point.

cond-mat.str-el↗

arXiv2026

Spin-triplet paired Wigner crystal stabilized by quantum geometry

We have used variational states to analyze the effects of band geometry on the two-dimensional Wigner crystal with one and two electrons per unit cell. At sufficiently low electron densities, we find that increasing Berry curvature drives a transition into a crystalline state composed of spin-triplet pairs carrying relative orbital angular momentum $m=-1$. The essential features of this transition are captured by an effective two-electron quantum dot problem in the presence of Berry curvature. Our results point to a purely electronic, strong-coupling mechanism for local spin-triplet pairing in correlated two-dimensional electron systems with quantum geometry.

cond-mat.str-el↗

arXiv2025

Electronic crystals in layered materials

In modern two-dimensional (2D) materials, such as graphene-based systems and atomically-thin transition-metal dichalcogenides, the interplay of strong electronic correlations, tunable moiré superlattices, and nontrivial band topology has given rise to rich phase diagrams and collective phenomena. Among the novel phases that have been realized, electronic crystals -- states of matter in which itinerant electrons spontaneously crystallize -- play a particularly prominent role. In this Review, we summarize the current status of electron crystallization in van der Waals heterostructures, with emphasis on the experimental platforms and measurement techniques that enable their study. We also highlight open questions and outline future directions that may elucidate more of the fascinating properties of electronic crystals.

cond-mat.str-el↗

arXiv2025

Quantum Critical Eliashberg Theory

Quantum criticality plays a central role in understanding non-Fermi liquid behavior and unconventional superconductivity in strongly correlated systems. In this review, we explore the quantum critical Eliashberg theory, which extends conventional Eliashberg approaches to non-Fermi liquid regimes governed by critical fluctuations. We discuss the theoretical foundations and recent developments in the field, focusing on the interplay between electronic interactions and bosonic modes near quantum phase transitions as described in the Yukawa-coupled version of the Sachdev-Ye-Kitaev model. Special emphasis is placed on the breakdown of quasiparticle coherence, anomalous scaling behaviour, Cooper pairing without quasiparticles, and emergent universality in different physical settings. Starting from a zero-dimensional "quantum-dot" model, we discuss the generalization to higher spatial dimensions and demonstrate the connection between quantum-critical Eliashberg theory and holographic superconductivity. Our analysis provides a perspective on how quantum criticality shapes the dynamics of strongly correlated metals and superconductors.

cond-mat.str-el↗

arXiv2025

Defect liquids in a weakly imbalanced bilayer Wigner Crystal

In a density-imbalanced bilayer Wigner crystal, where the ratio of electron densities in separate layers deviates slightly from unity, defects spontaneously form in one or both layers in the ground state of the system. Due to quantum tunneling, these defects become mobile and the system becomes a defect liquid. Motivated by this idea, we numerically study the semiclassical energetics of individual and paired point defects in the bilayer Wigner crystal system. We use these results in combination with a simple defect model to map the phase diagram of the defect liquid as a function of electron density and interlayer distance. Our results should be relevant for present experimental bilayer Wigner crystal systems.

cond-mat.str-el↗

arXiv2025

Magnetism from multiparticle ring exchange in moiré Wigner crystals

We investigate the multiparticle ring exchange couplings of the two-dimensional triangular Wigner crystal in external commensurate triangular and honeycomb potentials, using a semiclassical approach valid in the regime where Coulomb interactions dominate over electronic kinetic energy. In this limit, increasing the strength of the potential drives a transition from a ferromagnet to a $120^\circ$ Néel antiferromagnet for both external potential types. In the triangular case, we find that the transition occurs already for a weak potential, whereas in the honeycomb case, it occurs when the potential is nearly two orders of magnitude larger. Our results are relevant to the magnetism of generalized Wigner crystal phases observed at certain rational fillings of the moiré superlattice in transition-metal dichalcogenide heterobilayers.

cond-mat.str-el↗

arXiv2025

Critical gate distance for Wigner crystallization in the two-dimensional electron gas

We report on the properties of the two-dimensional electron gas in a dual-gate geometry, using quantum Monte Carlo methods to obtain aspects of the phase diagram as a function of electron density and gate distance. We identify the critical gate distance below which the Wigner crystal phase disappears. For larger gate distances, the system undergoes a re-entrant transition from crystal to liquid at sufficiently low density. We also present preliminary evidence for a fully polarized ferromagnetic liquid state at low electron density and intermediate gate distances. The quantum Monte Carlo results are compared with simpler approximate methods, which are shown to be semi-quantitatively reliable for determining key features of the phase diagram. These methods are then used to obtain the phase boundary between the Wigner crystal and liquid in the single-gate geometry.

cond-mat.str-el↗

arXiv2024

Strange metal and superconductor in the two-dimensional Yukawa-Sachdev-Ye-Kitaev model

The two-dimensional Yukawa-Sachdev-Ye-Kitaev (2d-YSYK) model provides a universal theory of quantum phase transitions in metals in the presence of quenched random spatial fluctuations in the local position of the quantum critical point. It has a Fermi surface coupled to a scalar field by spatially random Yukawa interactions. We present full numerical solutions of a self-consistent disorder averaged analysis of the 2d-YSYK model in both the normal and superconducting states, obtaining electronic spectral functions, frequency-dependent conductivity, and superfluid stiffness. Our results reproduce key aspects of observations in the cuprates as analyzed by Michon et al. (arXiv:2205.04030). We also find a regime of increasing zero temperature superfluid stiffness with decreasing superconducting critical temperature, as is observed in bulk cuprates.

cond-mat.str-el↗

arXiv2024

Spin mechanism of drag resistance in strongly correlated electron liquids

We investigate the effect of Coulomb drag resistance in a bilayer system of strongly correlated electron liquids magnetized by an in-plane field employing the framework of hydrodynamic theory. We identify a mechanism for drag magnetoresistance, which physically arises from the spin diffusion driven by fluctuations of the spin currents within a partially spin-polarized fluid. This effect is further enhanced by acoustic and optic plasmon resonances within the bilayer, where hydrodynamic plasmons are driven by fluctuating viscous stresses. We express the drag magnetoresistivity in terms of the intrinsic dissipative coefficients and basic thermodynamic properties of the electron fluid. Our results are derived nonperturbatively in interaction strength and do not rely on assuming Fermi-liquid behavior of the electron liquid, and applicable also in the regimes of semiquantum and highly correlated classical fluids.

cond-mat.str-el↗

arXiv2024

Magnetism of the Bilayer Wigner Crystal

The multiple-spin exchange frequencies of the bilayer Wigner crystal are determined by the semiclassical method, which is asymptotically exact in the limit of dilute electron densities. The evolution of the exchange frequencies with interlayer distance -- as the crystal undergoes a sequence of structural transitions -- leads to both ferromagnetic and multi-sublattice antiferromagnetic phases. Extrapolation of the results to higher density suggests a rich magnetic phase diagram of the bilayer Wigner crystal, including the possibility of spin-nematic and valence-bond solid phases. The bilayer crystal is stable to higher electron densities than the monolayer, leading to enhanced magnetic energy scales. Our estimates of the exchange energies suggest some of the magnetic phases may be accessible in recently discovered bilayer Wigner crystals in a transition-metal dichalcogenide system.

cond-mat.str-el↗

arXiv2023

Observation of an electronic microemulsion phase emerging from a quantum crystal-to-liquid transition

Strongly interacting electronic systems possess rich phase diagrams resulting from the competition between different quantum ground states. A general mechanism that relieves this frustration is the emergence of microemulsion phases, where regions of different phase self-organize across multiple length scales. The experimental characterization of these phases often poses significant challenges, as the long-range Coulomb interaction microscopically mingles the competing states. Here, we use cryogenic reflectance and magneto-optical spectroscopy to observe the signatures of the mixed state between an electronic Wigner crystal and an electron liquid in a MoSe2 monolayer. We find that the transit into this 'microemulsion' state is marked by anomalies in exciton reflectance, spin susceptibility, and Umklapp scattering, establishing it as a distinct phase of electronic matter. Our study of the two-dimensional electronic microemulsion phase elucidates the physics of novel correlated electron states with strong Coulomb interactions.

cond-mat.str-el↗

arXiv2023

Dynamical defects in a two-dimensional Wigner crystal: self-doping and kinetic magnetism

We study the quantum dynamics of interstitials and vacancies in a two-dimensional Wigner crystal (WC) using a semi-classical instanton method that is asymptotically exact at low density, i.e., in the $r_s\to \infty$ limit. The dynamics of these point defects mediates magnetism with much higher energy scales than the exchange energies of the pure WC. Via exact diagonalization of the derived effective Hamiltonians in the single-defect sectors, we find the dynamical corrections to the defect energies. The resulting expression for the interstitial (vacancy) energy extrapolates to 0 at $r_s = r_{\rm mit} \approx 70$ ($r_s \approx 30$), suggestive of a self-doping instability to a partially melted WC for some range of $r_s$ below $r_{\rm mit}$. We thus propose a "metallic electron crystal'' phase of the two-dimensional electron gas at intermediate densities between a low density insulating WC and a high density Fermi fluid.

cond-mat.str-el↗

arXiv2023

Local noise spectroscopy of Wigner crystals in two-dimensional materials

We propose to use local electromagnetic noise spectroscopy as a versatile and noninvasive tool to study Wigner crystal phases of strongly-interacting two-dimensional electronic systems. In-plane imaging of the local noise is predicted to enable single-site resolution of the electron crystal when the sample-probe distance is less than the inter-electron separation. At larger sample-probe distances, noise spectroscopy encodes information about the low-energy Wigner crystal phonons, including the dispersion of the transverse shear mode, the pinning resonance due to disorder, and optical modes emerging, for instance, in bilayer crystals. We discuss the potential utility of local noise probes in analyzing the rich set of phenomena expected to occur in the vicinity of the melting transition.

cond-mat.str-el↗