arXiv subjects

Anatoly Kuklov

Publications and source records attributed to Anatoly Kuklov.

At least 19 recordsLinked to original sources

arXiv2025

Field Theory of Borromean Super-counterfluids

We introduce a class of dynamical field theories for $N$-component "Borromean" ($N\geq 3$) super-counterfluid order, naturally formulated in terms of inter-species bosonic fields $\psi_{\alpha\beta}$. Their condensation breaks the normal-state [U(1)]$^N$ symmetry down to its diagonal U(1) subgroup, thereby encoding the arrest of the net superflow. This approach broadens our understanding of dynamical properties of super-counterfluids, at low energies capturing its universal properties, phase transition, counterflow vortices, and many of its other properties. Such super-counterfluid strikingly exhibits $N$ distinct flavors of energetically stable elementary vortex solutions, despite $\mathbb{Z}^{N-1}$ homotopy group of its $N\! -\! 1$ independent Goldstone modes, with $N\! -\! 1$ topologically distinct elementary vortex types, obeying modular arithmetic. The model leads to Borromean hydrodynamics as a low-energy theory, reveals counteflow AC Josephson effect, and generically predicts a first-order character of the phase transitions into Borromean super-counterfluid state in dimensions greater than two.

cond-mat.quant-gas↗

arXiv2025

Dual view of the Z$_2$-Gauged XY Model in 3D

The $Z_2$ gauged neutral XY model is of long-standing interest both in the context of nematic order, and the study of fractionalization and superconductivity. This paper presents heuristic arguments that no deconfinement of the XY field occurs in this model and presents results of a large-scale Monte Carlo simulations on a cubic lattice which are consistent with this conclusion. The correlation radius determining the confinement is found to be growing rapidly as a function of the parameters in the phase featuring the nematic order. Thus, mesoscopic properties of the system can mimic deconfinement with high accuracy in some part of the phase diagram.

cond-mat.supr-con↗

arXiv2024

Phonon-induced modification of polaritonic Rabi oscillations in the presence of the dark excitonic condensate

Optically inactive (dark) intervalley momentum-forbidden excitons are characterized by relatively long life time, and therefore are desirable candidates for realizing collective excitonic phases. However, testing their coherence by light directly is impossible. Here we propose a method for detecting a dark excitonic condensate. It relies on the interaction between excitons and phonons responsible for the interconversion between bright and dark excitons. As long as the dark condensate forms, the Rabi oscillations between photons and bright excitons can become strongly modified, and can be viewed as the photon-exciton-phonon polaritonic effect. The multi-component nature of the dark condensate consistent with the point-group symmetry is taken into account in the limit of weak phonon-exciton interaction. A perspective for the case of the strong interaction leading to the polaronic effect is discussed.

cond-mat.mes-hall↗

arXiv2024

Superconductivity of bipolarons from quadratic electron-phonon interaction

In systems with linear electron-phonon interaction (EPI), bound states of polarons, or bipolarons, form by gaining energy from the lattice deformation. The quadratic EPI case is fundamentally different: bipolarons form because electrons lose less energy when the total charge density is "compacted". As the coupling constant is increased, the bipolarons first appear as extended (but finite radius) soliton-type states. They subsequently decrease in radius until their size reaches the inter-atomic scale. We present the first numerically exact solution of the bipolaron problem from quadratic EPI in the presence of both on-site Hubbard and long-range Coulomb repulsion, and compute estimates of the largest superconducting transition temperature within the bipolaron mechanism. We find that $T_c/\Omega$ ratios, where $\Omega$ is the optical phonon frequency, can be several times larger than what one may expect from the linear EPI provided the phonon frequency is increased by orders of magnitude on occupied sites. Electron-electron repulsion can be tolerated at the expense of stronger EPI and the most detrimental effect comes from the Coulomb potential because it easily eliminates extended soliton states.

cond-mat.str-el↗

arXiv2024

Autonomous dynamics of two-dimensional insulating domain with superclimbing edges

Superclimbing dynamics is the signature feature of transverse quantum fluids describing wide superfluid one-dimensional interfaces and/or edges with negligible Peierls barrier. Using Lagrangian formalism, we show how the essence of the superclimb phenomenon -- dynamic conjugation of the fields of the superfluid phase and geometric shape -- clearly manifests itself via characteristic modes of autonomous motion of the insulating domain (``droplet") with superclimbing edges. In the translation invariant case and in the absence of supercurrent along the edge, the droplet demonstrates ballistic motion with the velocity-dependent shape and zero bulk currents. In an isotropic trapping potential, the droplet features a doubly degenerate sloshing mode. The period of the ground-state evolution of the superfluid phase (dictating the frequency of the AC Josephson effect) is sensitive to the geometry of the droplet. The supercurrent along the edge dramatically changes the droplet dynamics: The motion acquires features resembling that of a 2D charged particle interacting with a perpendicular magnetic field. In a linear external potential (uniform force field), the state with a supercurrent demonstrates a spectacular gyroscopic effect -- uniform motion in the perpendicular to the force direction.

cond-mat.quant-gas↗

arXiv2024

Transverse Quantum Superfluids

Even when ideal solids are insulating, their states with crystallographic defects may have superfluid properties. It became clear recently that edge dislocations in $^4$He featuring a combination of microscopic quantum roughness and superfluidity of their cores may represent a new paradigmatic class of quasi-one-dimensional superfluids. The new state of matter, termed transverse quantum fluid (TQF), is found in a variety of physical setups. The key ingredient defining the class of TQF systems is infinite compressibility, which is responsible for all other unusual properties such as the quadratic spectrum (or even the absence) of normal modes, irrelevance of the Landau criterion, off-diagonal long-range order at $T = 0$, and the exponential dependence of the phase slip probability on the inverse flow velocity. From a conceptual point of view, the TQF state is a striking demonstration of the conditional character of many dogmas associated with superfluidity, including the necessity of elementary excitations, in general, and the ones obeying Landau criterion in particular.

cond-mat.quant-gas↗

arXiv2024

Superclimbing modes in transverse quantum fluids: signature statistical and dynamical features

Superclimbing modes are hallmark degrees of freedom of transverse quantum fluids describing wide superfluid one-dimensional interfaces and/or edges with negligible Peierls barrier. We report the first direct numeric evidence of quantum shape fluctuations -- caused by superclimbing modes -- in simple lattice models, as well as at the free edge of an incomplete solid monolayer of $^4$He adsorbed on graphite. Our data unambiguously reveals the defining feature of the superclimbing modes -- canonical conjugation of the edge displacement field to the field of superfluid phase -- and its unexpected implication, i.e., that superfluid stiffness can be inferred from density snapshots.

cond-mat.other↗

arXiv2024

Transverse Quantum Fluids

Motivated by remarkable properties of superfluid edge dislocations in solid Helium-4, we discuss a broad class of quantum systems -- boundaries in phase separated lattice states, magnetic domain walls, and ensembles of Luttinger liquids -- that can be classified as Transverse Quantum Fluids (TQF). After introducing the general idea of TQF, we focus on a coupled array of Luttinger liquids forming an incoherent TQF. This state is a long-range ordered quasi-one-dimensional superfluid, topologically protected against quantum phase slips by tight-binding of instanton dipoles, that has no coherent quasi-particle excitations at low energies. Incoherent TQF is a striking example of the irrelevance of the Landau quasiparticle criterion for superfluidity in systems that lack Galilean invariance. We detail its phenomenology, to motivate a number of experimental studies in condensed matter and cold atomic systems.

cond-mat.other↗

arXiv2023

Universal Correlations as Fingerprints of Transverse Quantum Fluids

We study universal off-diagonal correlations in transverse quantum fluids (TQF) -- a new class of quasi-one-dimensional superfluids featuring long-range-ordered ground states. These exhibit unique self-similar space-time relations scaling with $x^2/Dτ$ that serve as fingerprints of the specific states. The results obtained with the effective field theory are found to be in perfect agreement with {\it ab initio} simulations of hard-core bosons on a lattice -- a simple microscopic realization of TQF. This allows an accurate determination -- at nonzero temperature and finite system size -- of such key ground-state properties as the condensate and superfluid densities, and characteristic parameter $D$.

cond-mat.other↗

arXiv2023

Soliton States From Quadratic Electron-Phonon Interaction

We present the first numerically exact study of self-trapped, a.k.a. soliton, states of electrons that form in materials with strong quadratic coupling to the phonon coordinates. Previous studies failed to observe predictions based on the variational approach in continuum space because soliton states form only when system parameters are taken to the extreme limit. At the variational level, we establish that finite-radius solitons emerge through the weak first-order transition as the coupling strength is increased, and subsequently collapse to the single-site state through strong first-order transition. Both transitions transform into smooth crossovers between the light and heavy polaron states in the full quantum treatment. The most surprising effect not observed in any other polaron model is non-monotonic dependence of the soliton effective mass and the residue at strong coupling.

cond-mat.str-el↗

arXiv2023

Superfluid Edge Dislocation: Transverse Quantum Fluid

Recently, it has been argued by Kuklov et al., that unusual features associated with the superflow-through-solid effect observed in solid He4 can be explained by unique properties of dilute distribution of superfluid edge dislocations. We demonstrate that stability of supercurrents controlled by quantum phase slips (instantons), and other exotic infrared properties of the superfluid dislocations readily follow from a one-dimensional quantum liquid distinguished by an effectively infinite compressibility (in the absence of Peierls potential) associated with the edge dislocation's ability to climb. This establishes a new class of quasi-one-dimensional superfluid states that remain stable and long-range ordered despite their low dimensionality. We propose an experiment to test our mass-current--pressure characteristic prediction.

cond-mat.other↗

arXiv2022

Polaron with Quadratic Electron-phonon Interaction

We present the first numerically exact study of a polaron with quadratic coupling to the oscillator displacement, using two alternative methodological developments. Our results cover both anti-adiabatic and adiabatic regimes and the entire range of electron-phonon coupling $g_2$, from the system's stability threshold at attractive $g_2=-1$ to arbitrary strong repulsion at $g_2 \gg 1$. Key properties of quadratic polarons prove dramatically different from their linear counterparts. They (i) are insensitive even to large quadratic coupling except in the anti-adiabatic limit near the threshold of instability at attraction; (ii) depend only on the adiabatic ratio but are insensitive to the electron dispersion and dimension of space; (iii) feature weak lattice deformations even at the instability point. Our results are of direct relevance to properties of electrons at low densities in polar materials, including recent proposals for their superconducting states.

cond-mat.str-el↗

arXiv2021

Anomalously Small Excitation Gaps as a Precursor of Dislocation Core Superfluidity in Solid Helium-4

In the vicinity of the insulator-to-superfluid quantum phase transition in its core, a dislocation in a He-4 crystal supports particle-hole excitations with arbitrary small gaps. These exotic analogs of Frenkel interstitial-vacancy pairs should manifest themselves in various threshold and thermoactivation effects. In Worm Algorithm simulations, we reveal the presence of corresponding small gaps via anomalous thermoactivation behavior of particle number fluctuations, which we unambiguously associate with dislocations by "visualization" techniques. Experimentally, the related threshold and thermoactivation dependencies could be observed in the ultrasound absorption.

cond-mat.soft↗

arXiv2021

Thermal and structural properties of topological defects in solid Helium-4: Strain induced martensitic transformation from hcp to fc orthorhombic lattice

Several experimental studies have reported thermally activated behavior of the mechanical response of solid Helium-4 which does not fit into the model of thermally activated Frenkel pairs in an ideal crystal. The purpose of the present work is to investigate how structural topological defects modify the response. Using quantum Monte Carlo Worm Algorithm, we study temperature dependence of fluctuations of the total number of particles in samples of hcp solid Helium-4 containing several types of dislocations. Such fluctuations can be described by the thermal activation law with the activation energy dependent strongly on the type of the dislocation and the crystal density. The extracted values cover a range from about 1K to 20K. It is also found that annihilation of a jog-antijog pair can produce a local region of the solid characterized by the orthorhombic symmetry. This serendipitous observation suggests that hcp solid Helium-4 can undergo a displacive phase transition into the orthorhombic crystal under uniaxial stress of about 10-15%

cond-mat.other↗

arXiv2019

Plasticity induced superclimb in solid Helium-4: Direct and inverse effects

During the last decade experimental evidence is building that the mass supertransport through solid Helium-4 as well as the anomalously large matter accumulation in the bulk -- the giant isochoric compressibility (aka the syringe effect) -- are both supported by a network of dislocations with superfluid core. However, a structure of this network as well as its relation to the basal (non-superfluid) dislocations which are responsible for plasticity remain unclear. Here it is shown that superclimbing and basal edge dislocations can form bound pairs. This implies that plastic deformation should produce the syringe effect and vice versa. The experimental test is proposed. While the strength of the effect depends on the average orientation of the paired dislocations, there is a feature unique for the superfluid dislocation scenario -- the supercurrents flow in the direction perpendicular to the plastic deformation.

cond-mat.other↗

arXiv2019

Phases and phase transitions of Bose condensed light: phase separation effect

Recent realization of Bose-Einstein condensation of light in 2D provides a new platform for studying novel phases and phase transitions. The combination of low effective mass of the confined light and the presence of the dye molecules with randomly oriented directions of the dipolar transition engages a competition between disorder and the tendency to forming algebraic off-diagonal order. The phase diagram of possible phases is constructed at the mean field level. One of the phases is the condensate of photon pairs induced solely by the orientational disorder. Such a {\it geometrical } mechanism of pairing has no analogy in other systems. It is also found that the photon condensantion can proceed as a phase separation effect leading to a non-uniform distribution of the condensate and dye molecules.

cond-mat.quant-gas↗

arXiv2018

Phases and phase transitions of Bose condensed light

Bose-Einstein condensation of light in 2D is characterized by two classical fields corresponding to two polarizations of light as well as by the distribution of dye molecules inducing light thermalization through dipolar transition. In the case when this transition is triple-degenerate the resulting field theory for the condensate of light is O(4) symmetric, which precludes algebraic long range order in 2D at any finite temperature $T$. If the dipolar degeneracy is removed, then, equilibrium phases with lower symmetries -- O(2)$\times$Z$_2$ and O(2) can emerge. Accordingly, algebraic off diagonal order of light condensate becomes possible. An orientationsl disorder introduced by local dipolar anisotropy can destroy algebraic order in one-photon density matrix while preserving it in the two-photon one. This represents formation of the condensate of photon pairs.

cond-mat.quant-gas↗

arXiv2018

Strong and weak field criticality of 2D liquid gas transition

Finite size scaling (FSS) analysis of the liquid gas criticality is complicated by the absence of any broken symmetry. This, in particular, does not allow a straightforward finding of the coexistence line and the critical point. The numerical flowgram (NF) method is adapted for a controlled determination of the coexistence line and the critical point, with the critical indices $μ,\, ν$ measured within 1-2% of the total error. The approach based on the NF for measuring the non-analytical corrections to the diameter - the mean density of the liquid and gas phases along the coexistence line - is outlined. Our analysis is a first step toward a general evaluation of isolated critical and multicritical points.

cond-mat.stat-mech↗