arXiv subjects

A. B. Kuklov

Publications and source records attributed to A. B. Kuklov.

At least 19 recordsLinked to original sources

arXiv2016

Comment on "Dislocation Structure and Mobility in hcp $^4$He"

In their Letter, Borda, Cai, and de Koning report the results of ab initio simulations of dislocations responsible for the giant plasticity. The authors claim key insights into the recent interpretations of (i) the giant plasticity and (ii) the mass flow junction experiments. The purpose of this Comment is clarifying the role of dislocations in the mass flow in conjunction with explaining that the part (ii) of the claim is misleading.

cond-mat.other↗

arXiv2015

Counterflow Superfluidity of Two-Species Ultracold Atoms in a Commensurate Optical Lattice

If two species of ultracold atoms are loaded in a sufficiently tight optical lattice at a commensurate total filling factor, the net number-of-atoms transport is suppressed by the Mott-Hubbard localization. Nonetheless, the counterflow low-frequency dynamics of the two components may survive. We consider corresponding effective Hamiltonians for the three classes of the two-species insulators-- fermion-fermion, boson-boson, and boson-fermion type-- and reveal the conditions when the resulting groundstate supports super-counter-fluidity (SCF) of the two components. Alternative groundstates are found to be phase-segregated states. We emphasize a crucial role of breaking the isotopic symmetry between the species for realizing the SCF phase.

cond-mat.soft↗

arXiv2013

Deconfined criticality flow in the Heisenberg model with ring-exchange interactions

Quantum transition points in the J -Q model---the test bed of the deconfined critical point theory---and the SU(2)-symmetric discrete noncompact CP^1 representation of the deconfined critical action are directly compared by the flowgram method. We find that the flows of two systems coincide in a broad region of linear system sizes (10 < L < 50 for the J -Q model), implying that the deconfined critical point theory correctly captures the mesoscopic physics of competition between the antiferromagnetic and valence-bond orders in quantum spin systems. At larger sizes, however, we observe significant deviations between the two flows which both demonstrate strong violations of scale invariance. This reliably rules out the second-order transition scenario in at least one of the two models and suggests the most likely explanation for the nature of the transition in the J-Q model.

cond-mat.str-el↗

arXiv2012

Parafermion excitations in superfluid of quasi-molecular chains

We study a quantum phase transition in a system of dipoles confined in a stack of $N$ identical one-dimensional lattices (tubes) polarized perpendicularly to the lattices. In this arrangement the intra-lattice interaction is purely repulsive preventing the system collapse and the inter-lattice one is attractive. The dipoles may represent polar molecules or indirect excitons. The transition separates two phases; in one of them superfluidity (understood as algebraic decay of the corresponding correlation functions) takes place in each individual lattice, in the other (chain superfluid) the order parameter is the product of bosonic operators from all lattices. We argue that in the presence of finite inter-lattice tunneling the transition belongs to the universality class of the $q=N$ two-dimensional classical Potts model. For $N=2,3,4$ the corresponding low energy field theory is the model of Z$_N$ parafermions perturbed by the thermal operator. Results of Monte Carlo simulations are consistent with these predictions. The detection scheme for the chain superfluid of indirect excitons is outlined.

cond-mat.other↗

arXiv2010

Glide and Superclimb of Dislocations in Solid $^4$He

Glide and climb of quantum dislocations under finite external stress, variation of chemical potential and bias (geometrical slanting) in Peierls potential are studied by Monte Carlo simulations of the effective string model. We treat on unified ground quantum effects at finite temperatures $T$. Climb at low $T$ is assisted by superflow along dislocation core -- {\it superclimb}. Above some critical stress avalanche-type creation of kinks is found. It is characterized by hysteretic behavior at low $T$. At finite biases gliding dislocation remains rough even at lowest $T$ -- the behavior opposite to non-slanted dislocations. In contrast to glide, superclimb is characterized by quantum smooth state at low temperatures even for finite bias. In some intermediate $T$-range giant values of the compressibility as well as non-Luttinger type behavior of the core superfluid are observed.

cond-mat.other↗

arXiv2009

Superclimb of Dislocations and the Anomalous Isochoric Compressibility of Solid He4

In the experiment on superfluid transport in solid He4 [PRL {\bf 100}, 235301 (2008)], Ray and Hallock observed an {\it anomalously large isochoric compressibility}: the supersolid samples demonstrated a significant and apparently spatially uniform response of density and pressure to chemical potential, applied locally through Vycor "electrodes". We propose that the effect is due to {\it superclimb} : edge dislocations can climb because of mass transport along superfluid cores. We corroborate the scenario by {\it ab initio} simulations of an edge dislocation in solid He4 at $T=0.5K$. We argue that at low temperature the effect must be suppressed due to a crossover to the smooth dislocation.

cond-mat.other↗

arXiv2008

Mechanical and superfluid properties of dislocations in solid He4

Dislocations are shown to be smooth at zero temperature because of the effective Coulomb-type interaction between kinks. Crossover to finite temperature rougnehing is suggested to be a mechanism responsible for the softening of \he4 shear modulus recently observed by Day and Beamish (Nature, {\bf 450}, 853 (2007)). We discuss also that strong suppresion of superfuidity along the dislocation core by thermal kinks can lead to locking in of the mechanical and superfluid responses.

cond-mat.stat-mech↗

arXiv2008

Search for Deconfined Criticality: SU(2) Déjà Vu

Monte Carlo simulations of the SU(2)-symmetric deconfined critical point action reveal strong violations of scale invariance for the deconfinement transition. We find compelling evidence that the generic runaway renormalization flow of the gauge coupling is to a weak first order transition, similar to the case of U(1)$\times$U(1) symmetry. Our results imply that recent numeric studies of the Nèel antiferromagnet to valence bond solid quantum phase transition in SU(2)-symmetric models were not accurate enough in determining the nature of the transition.

cond-mat.stat-mech↗

arXiv2008

Local stress and superfluid properties of solid Helium-4

More than half a century ago Penrose asked: are the superfluid and solid state of matter mutually exclusive or do there exist "supersolid" materials where the atoms form a regular lattice and simultaneously flow without friction? Recent experiments provide evidence that supersolid behavior indeed exists in Helium-4 -- the most quantum material known in Nature. In this paper we show that large local strain in the vicinity of crystalline defects is the origin of supersolidity in Helium-4. Although ideal crystals of Helium-4 are not supersolid, the gap for vacancy creation closes when applying a moderate stress. While a homogeneous system simply becomes unstable at this point, the stressed core of crystalline defects (dislocations and grain boundaries) undergoes a radical transformation and can become superfluid.

cond-mat.stat-mech↗

arXiv2007

Superfluidity of Grain Boundaries in Solid Helium-4

By large-scale quantum Monte Carlo simulations we show that grain boundaries in Helium-4 crystals are generically superfluid at low temperature, with a transition temperature of the order of ~0.5K at the melting pressure; insulating grain boundaries are found only for special orientations of the grains. We also find that close vicinity to the melting line is not a necessary condition for superfluid grain boundaries, and a grain boundary in direct contact with the superfluid liquid at the melting curve is found to be mechanically stable and the grain boundary superfluidity observed by Sasaki et al. [Science 313, 1098 (2006)] is not just a crack filled with superfluid.

cond-mat.stat-mech↗

arXiv2007

Luttinger Liquid in the Core of Screw Dislocation in Helium-4

On the basis of first-principle Monte Carlo simulations we find that the screw dislocation along the hexagonal axis of an hcp He4 crystal features a superfluid core. This is the first example of a regular quasi-one-dimensional supersolid, and one of the cleanest cases of a regular Luttinger-liquid system. In contrast, the same type of screw dislocation in solid Hydrogen is insulating.

cond-mat.other↗

arXiv2006

Unconventional strongly interacting Bose-Einstein condensates in optical lattices

Feschbach resonances in a non-s-wave channel of two-component bosonic mixtures can induce atomic Bose Einstein condensates with a non-zero orbital momentum in the optical lattice, if one component is in the Mott insulator state and the other is not. Such non-s-wave condensates break the symmetry of the lattice and, in some cases, time-reversal symmetry. They can be revealed in specific absorption imaging patterns.

cond-mat.other↗

arXiv2006

Imaging of critical correlations in optical lattices and atomic traps

We consider critical space-time correlations in trapped utracold atoms and propose a method for their detection by the interference with a reference Bose-Einstein condensate. An important information about universal properties can be obtained despite non-uniformity and small sizes of atomic clouds. The advantage of this method is that the correlation properties of the interference pattern are robust with respect to expansion and are not, practically, affected by microscopic structure of underlying lattice including structural disorder. The non-destructive scheme allows measuring the space-time correlators of arbitrary order.

cond-mat.other↗

arXiv2005

Atomic Josephson vortex

We show that Josephson vortices in a quasi-1D atomic Bose Josephson junction can be controllably manipulated by imposing a difference of chemical potentials on the atomic BEC waveguides forming the junction. This effect, which has its origin in the Berry phase structure of a vortex, turns out to be very robust in the whole range of the parameters where such vortices can exist. We also propose that a Josephson vortex can be created by the phase imprinting technique and can be identified by a specific tangential feature in the interference picture produced by expanding clouds released from the waveguides.

cond-mat.other↗

arXiv2005

Drag effect and topological complexes in strongly interacting two-component lattice superfluids

The mutual drag in strongly interacting two-component superfluids in optical lattices is discussed. Two competing drag mechanisms are the vacancy-assisted motion and proximity to the quasi-molecular state, in which an integer number $q$ of atoms (or holes) of one component might be bound to one atom (or hole) of the other component. Then the lowest energy topological excitation (vortex or persistent current) becomes a composite object consisting of $q$ circulation quanta of one component and one circulation of the other. In the SQUID-type geometry, the value of $q$ can become fractional. These topological complexes can be detected by absorptive imaging. We present both the mean field and Monte Carlo results. The drag effects in optical lattices are drastically different from the Galilean invariant Andreev-Bashkin effect in liquid helium.

cond-mat.soft↗

arXiv2004

Interconversion of dark soliton and Josephson vortex in a quasi-1D long Bose Josephson junction

Dark soliton (DS) and Josephson vortex (JV) in quasi-1D long Bose Josephson junction (BJJ) can be interconverted by tuning Josephson coupling. Rates of the interconversion as well as of the thermally activated phase-slip effect, resulting in the JV switching its vorticity, have been evaluated. The role of quantum phase-slip in creating superposition of JVs with opposite vorticities as a qubit is discussed as well. Utilization of the JV for controlled and coherent transfer of atomic Bose-Einstein condensate (BEC) is suggested.

cond-mat.soft↗

arXiv2003

Inertial mass of a superconducting vortex

We show that a large contribution to the inertial mass of a moving superconducting vortex comes from transversal displacements of the crystal lattice. The corresponding part of the mass per unit length of the vortex line is $M_{l} = ({\rm m}_e^2c^{2}/64πα^{2}μλ_{L}^{4})\ln(λ_{L}/ξ)$ , where ${\rm m}_{e}$ is the the bare electron mass, $c$ is the speed of light, $α=e^{2}/{\hbar}c {\approx} 1/137$ is the fine structure constant, $μ$ is the shear modulus of the solid, $λ_{L}$ is the London penetration length and $ξ$ is the coherence length. In conventional superconductors, this mass can be comparable to or even greater than the vortex core mass computed by Suhl.

cond-mat.supr-con↗

arXiv2002

Decoherence of a Superposition of Macroscopic Current States in a SQUID

We show that fundamental conservation laws mandate parameter-free mechanisms of decoherence of quantum oscillations of the superconducting current between opposite directions in a SQUID -- emission of phonons and photons at the oscillation frequency. The corresponding rates are computed and compared with experimental findings. The decohering effects of external mechanical and magnetic noise are investigated.

cond-mat.mes-hall↗