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S. Khlebnikov

Publications and source records attributed to S. Khlebnikov.

At least 19 recordsLinked to original sources
arXiv2014

Relaxation dynamics in a strongly coupled Fermi superfluid

The key feature of time-dependent dynamics in a paired Fermi superfluid is the presence of a large number of independent degrees of freedom---the pairing amplitudes of fermions with different momenta. We argue that useful prototypes of this dynamics come from D-brane constructions of string theory. Using a specific example of that kind, we identify the mechanism by which a strongly coupled Fermi superfluid relaxes to equilibrium; it involves a wave of excitation in the momentum space, propagating from the Fermi surface towards the ultraviolet. For a sudden quench induced by a change in the fermion coupling, we find that the relaxation occurs rapidly, over only a few oscillations of the quasiparticle gap.

hep-th↗
arXiv2009

Electroweak symmetry breaking as a proximity effect

The proximity effect in condensed matter physics is a mechanism that naturally produces weak superconductivity. We argue that a braneworld can similarly produce a low-energy breaking of the electroweak symmetry, provided that in addition to the "normal" region, occupied by the conventional phase of QCD, there is a bulk region where the color is in an anisotropic (layered) state with a larger confinement scale. The W and Z bosons, as well as the quarks, acquire masses by scattering off the layered region. A peculiar feature of this scenario is that the strongly interacting sector responsible for the symmetry breaking can be much lighter than the conventional 1 TeV.

hep-ph↗
arXiv2008

Quantum mechanics of superconducting nanowires

In a short superconducting nanowire connected to bulk superconducting leads, quantum phase slips behave as a system of linearly (as opposed to logarithmically) interacting charges. This system maps onto quantum mechanics of a particle in a periodic potential. We show that, while the state with a high density of phase slips is not a true insulator (a consequence of Josephson tunneling between the leads), for a range of parameters it behaves as such down to unobservably small temperatures. We also show that quantum phase slips give rise to multiple branches (bands) in the energy-current relation and to an interband ("exciton") mode.

cond-mat.supr-con↗
arXiv2008

Classical thermodynamics of gravitational collapse

We study numerically gravitational collapse of a spherically symmetric instanton particle in five dimensions. We show that the late stages of the process are characterized by a nearly constant ``free energy'', the value of which matches (within numerical uncertainties) the value obtained from standard black-hole thermodynamics. This suggests a purely classical interpretation of the free energy of a black hole.

hep-th↗
arXiv2008

Quantum phase slips in a confined geometry

We consider tunneling of vortices across a superconducting film that is both narrow and short (and connected to bulk superconducting leads at the ends). We find that in the superconducting state the resistance, at low values of the temperature (T) and current, does not follow the power-law dependence on T characteristic of longer samples but is exponential in 1/T. The coefficient of 1/T in the exponent depends on the length or, equivalently, the total normal-state resistance of the sample. These conclusions persist in the one-dimensional limit, which is similar to the problem of quantum phase slips in an ultra-narrow short wire.

cond-mat.supr-con↗
arXiv2007

Electron as soliton: Nonlinear theory of dielectric polarization

We describe a class of theories of dielectric polarization and a species of solitons in these theories. The solitons, made entirely out of the polarization field, have quantized values of the electric charge and can be interpreted as electrons and holes. A soliton-antisoliton pair is an exciton. We present numerical evidence that the elementary soliton is stable.

cond-mat.mes-hall↗
arXiv2007

Bulk black hole, escaping photons, and bounds on violations of Lorentz invariance

There are reasons (which we enumerate) to think that an infinite extra dimension will harbor a black hole. In this case, brane-localized modes of gravity and gauge fields become quasilocalized, and light from a distant object can become extinct as it is lost to the black hole. In a concrete scenario, where the photon is localized by gravity, we find that the extinction rate for propagating photons is at least comparable to the correction to the real part of the frequency. That results, for example, in a stringent bound on renormalization of the speed of light.

hep-ph↗
arXiv2006

Massive Schwinger model with a finite inductance: theta-(in)dependence, the U(1) problem, and low-energy theorems

Gauge theories embedded into higher-dimensional spaces with certain topologies acquire inductance terms, which reflect the energy cost of topological charges accumulated in the extra dimensions. We compute topological susceptibility in the strongly-coupled two-flavor massive Schwinger model with such an inductance term and find that it vanishes, due to the contribution of a global low-energy mode (a ``global axion''). This is in accord with the general argument on the absence of theta-dependence in such topologies. Because the mode is a single oscillator, there is no corresponding particle, and the solution to the U(1) problem is unaffected.

hep-th↗
arXiv2005

Piezoelectric coupling, phonons, and tunneling into a quantum Hall edge

We show that the piezoelectric coupling to three-dimensional phonons in GaAs renormalizes the current-voltage exponent for tunneling of electrons into an incompressible quantum Hall edge. The leading correction is always negative, in agreement with experiments on the $ν= 1/3$ state and, depending on the precise value of the edge plasmon speed, can be as large as a few percent. We also discuss higher-order corrections, which determine the effect of the piezoelectric coupling in the extreme infrared limit.

cond-mat.mes-hall↗
arXiv2005

Magnus Force in Discrete and Continuous Two-Dimensional Superfluids

Motion of vortices in two-dimensional superfluids in the classical limit is studied by solving the Gross-Pitaevskii equation numerically on a uniform lattice. We find that, in the presence of a superflow directed along one of the main lattice periods, vortices move with the superflow on fine lattices but perpendicular to it on coarse ones. We interpret this result as a transition from the full Magnus force in the Galilean-invariant limit to vanishing effective Magnus force in a discrete system, in agreement with the existing experiments on vortex motion in Josephson junction arrays.

cond-mat.supr-con↗
arXiv2005

Quantum phase slips in the presence of finite-range disorder

To study the effect of disorder on quantum phase slips (QPS) in superconducting wires, we consider the plasmon-only model where disorder can be incorporated into a first-principles instanton calculation. We consider weak but general finite-range disorder and compute the formfactor in the QPS rate associated with momentum transfer. We find that the system maps onto dissipative quantum mechanics, with the dissipative coefficient controlled by the wave (plasmon) impedance Z of the wire and with a superconductor-insulator transition at Z=6.5 kOhm. We speculate that the system will remain in this universality class after resistive effects at the QPS core are taken into account.

cond-mat.mes-hall↗
arXiv2005

Classical stability of supercurrent in one dimension: a numerical study

We report results of a classical simulation of thermal phase slips, and the associated relaxation of supercurrent, in a ring-shaped one-dimensional superfluid. We find that the classical relaxation rate vanishes in the uniform limit. This leaves the quantum relaxation, with momentum transfer to phonons, the only mechanism of supercurrent decay in the uniform system. In the presence of a smooth periodic potential, classical decay becomes possible, and we identify a family of moving critical droplets that can mediate it.

cond-mat.supr-con↗
arXiv2004

Brane-worlds and theta-vacua

Reductions from odd to even dimensionalities ($5\to 4$ or $3\to 2$), for which the effective low-energy theory contains chiral fermions, present us with a mismatch between ultraviolet and infrared anomalies. This applies to both local (gauge) and global currents; here we consider the latter case. We show that the mismatch can be explained by taking into account a change in the spectral asymmetry of the massive modes--an odd-dimensional analog of the phenomenon described by the Atiyah-Patodi-Singer theorem in even dimensionalities. The result has phenomenological implications: we present a scenario in which a QCD-like $θ$-angle relaxes to zero on a certain (possibly, cosmological) timescale, despite the absence of any light axion-like particle.

hep-th↗
arXiv2004

Tunneling in a uniform one-dimensional superfluid: emergence of a complex instanton

In a uniform ring-shaped one-dimensional superfluid, quantum fluctuations that unwind the order parameter need to transfer momentum to quasiparticles (phonons). We present a detailed calculation of the leading exponential factor governing the rate of such phonon-assisted tunneling in a weakly-coupled Bose gas at a low temperature $T$. We also estimate the preexponent. We find that for small superfluid velocities the $T$-dependence of the rate is given mainly by $\exp(-c_s P/ 2T)$, where $P$ is the momentum transfer, and $c_s$ is the phonon speed. At low $T$, this represents a strong suppression of the rate, compared to the non-uniform case. As a part of our calculation, we identify a complex instanton, whose analytical continuation to suitable real-time segments is real and describes formation and decay of coherent quasiparticle states with nonzero total momenta.

cond-mat.other↗
arXiv2004

Quasiparticle scattering by quantum phase slips in one-dimensional superfluids

Quantum phase slips (QPS) in narrow superfluid channels generate momentum by unwinding the supercurrent. In a uniform Bose gas, this momentum needs to be absorbed by quasiparticles (phonons). We show that this requirement results in an additional exponential suppression of the QPS rate (compared to the rate of QPS induced by a sharply localized perturbation). In BCS-paired fluids, momentum can be transferred to fermionic quasiparticles, and we find an interesting interplay between quasiparticle scattering on QPS and on disorder.

cond-mat.soft↗
arXiv2003

Numerical study of induced vortex tunneling

Tunneling of vortex-antivortex pairs across a superconducting film can be controlled via inductive coupling of the film to an external circuit. We study this process numerically in a toroidal film (periodic boundary conditions in both directions) by using the dual description of vortices, in which they are represented by a fundamental quantum field. We compare the results to those obtained in the instanton approach.

quant-ph↗
arXiv2003

Induced vortex tunneling in a superconducting wire

We consider induced topological transitions in a wire made from cylindrical superconducting film. During a transition, a pulse of electric current causes transport of a virtual vortex-antivortex pair around the cylinder. We consider both the instanton approach, in which the transition is viewed as motion of vortices in the Euclidean time, and the real-time dual formulation, in which vortices are described by a fundamental quantum field. The instanton approach is convenient to discuss effects of the environment, while in the dual formulation we show that there exists a potentially useful adiabatic regime, in which the probability to create a real vortex pair is exponentially suppressed, but the total transport of the vortex number can be of order one.

quant-ph↗