arXiv subjects

Baruch Horovitz

Publications and source records attributed to Baruch Horovitz.

At least 37 records · Page 2Linked to original sources

arXiv2012

Single vortex fluctuations in a superconducting chip as generating dephasing and spin flips in cold atom traps

We study trapping of a cold atom by a single vortex line in an extreme type II superconducting chip, allowing for pinning and friction. We evaluate the atom's spin flip rate and its dephasing due to the vortex fluctuations in equilibrium and find that they decay rapidly when the distance to the vortex exceeds the magnetic penetration length. We find that there are special spin orientations, depending on the spin location relative to the vortex, at which spin dephasing is considerably reduced while perpendicular directions have a reduced spin flip rate. We also show that the vortex must be perpendicular to the surface for a general shape vortex.

cond-mat.supr-con↗

arXiv2011

Surface plasmons at composite surfaces with diffusive charges

Metal surfaces with disorder or with nanostructure modifications are studied, allowing for a localized charge layer (CL) in addition to continuous charges (CC) in the bulk, both charges having a compressional or diffusive non-local response. The notorious problem of "additional boundary conditions" is resolved with the help of a Boltzmann equation that involves the scattering between the two charge types. Depending on the strength of this scattering, the oscillating charges can be dominantly CC or CL; the surface plasmon (SP) resonance acquires then a relatively small linewidth, in agreement with a large set of data. With a few parameters our model describes a large variety of SP dispersions corresponding to observed data.

cond-mat.mes-hall↗

arXiv2011

Rings and boxes in dissipative environments

We study a particle on a ring in presence of a dissipative Caldeira-Leggett environment and derive its response to a DC field. We find, through a 2-loop renormalization group analysis, that a large dissipation parameter $η$ flows to a fixed point $η_R=η_c=\hbar/2π$. We also reexamine the mapping of this problem to that of the Coulomb box and show that the relaxation resistance, of recent interest, is quantized for large $η$. For finite $η>η_c$ we find that a certain average of the relaxation resistance is quantized. We propose a box experiment to measure a quantized noise.

cond-mat.mes-hall↗

arXiv2011

Shot noise in a Majorana fermion chain

We calculate the shot noise power in a junction of a network of Majorana bound states (MBS) with a normal metal. These Majorana bound states are on the border of alternative ferromagnetic and superconducting regions at the quantum spin Hall insulator edge. We analyze different realization of MBS networks including a few isolated ones or in a chain allowing for the limit of weak and strong tunneling. The conductance, as well as the shot noise are considerably stronger than those of a weakly coupled normal-superconduting junction, being a hallmark of the MBS. We find that the Fano factor is quantized $F=2$ when one MBS member of a pair is coupled to the lead, however if both MBS members are coupled $F$ is non-integer.

cond-mat.mes-hall↗

arXiv2010

The Aharonov-Bohm effect in presence of dissipative environments

We study a particle on a ring in presence of various dissipative environments. We develop and solve a variational scheme assuming low frequency dominance. Our solution produces a renormalization group (RG) transformation to all orders in the inverse dissipation strength, and in particular reproduces known two loop results. Our RG leads to a weak dissipation parameter, for which a weak coupling expansion for the position correlation function shows a 1/t^2 decay in imaginary time.

cond-mat.mes-hall↗

arXiv2010

Shot noise in Graphene with long range Coulomb interaction and the local Fermi distribution

We calculate the shot noise power in ballistic graphene using the kinetic equation approach based on the Keldysh technique. We find that the local energy distribution function obeys Poisson's equation, indicating a mapping into a diffusive metal system. We derive the conductance and noise including the long range Coulomb interaction to first order. We find that the shot noise increases due to interaction, leading to a frequency dependence. Furthermore, we find that the Fano factor at degeneracy is 1/3, the same as without the Coulomb interaction.

cond-mat.mes-hall↗

arXiv2009

Winding of planar gaussian processes

We consider a smooth, rotationally invariant, centered gaussian process in the plane, with arbitrary correlation matrix $C_{t t'}$. We study the winding angle $ϕ_t$ around its center. We obtain a closed formula for the variance of the winding angle as a function of the matrix $C_{tt'}$. For most stationary processes $C_{tt'}=C(t-t')$ the winding angle exhibits diffusion at large time with diffusion coefficient $D = \int_0^\infty ds C'(s)^2/(C(0)^2-C(s)^2)$. Correlations of $\exp(i n ϕ_t)$ with integer $n$, the distribution of the angular velocity $\dot ϕ_t$, and the variance of the algebraic area are also obtained. For smooth processes with stationary increments (random walks) the variance of the winding angle grows as ${1/2} (\ln t)^2$, with proper generalizations to the various classes of fractional Brownian motion. These results are tested numerically. Non integer $n$ is studied numerically.

cond-mat.stat-mech↗

arXiv2008

Particle renormalizations in presence of dissipative environments

We study the Aharonov-Bohm oscillations of a charged particle on a ring of radius R coupled to a dirty metal environment. With Monte-Carlo methods we evaluate the curvature of these oscillations which has the form 1/M*R^2, where M* is an effective mass. We find that at low temperatures T the curvature approaches at large R>l an R independent M*>M, where l is the mean free path in the metal. This behavior is also consistent with perturbation theory in the particle - metal coupling parameter. At finite temperature T we identify dephasing lengths that scale as T^{-1} at R>l and as T^{-1/4} at R<<l.

cond-mat.mes-hall↗

arXiv2008

Noise from metallic surfaces -- effects of charge diffusion

Non-local electrodynamic models are developed for describing metallic surfaces for a diffusive metal. The electric field noise at a distance z_0 from the surface is evaluated and compared with data from ion chips that show anomalous heating with a noise power decaying as z_0^{-4}. We find that high surface diffusion can account for the latter result.

quant-ph↗

arXiv2008

Gauge field induced by ripples in graphene

We study the effects of quenched height fluctuations (ripples) in graphene on the density of states (DOS). We show that at strong ripple disorder a divergence in the DOS can lead to an ordered ground state. We also discuss the formation of dislocations in corrugated systems, buckling effects in suspended samples, and the changes in the Landau levels due to the interplay between a real magnetic field and the gauge potential induced by ripples.

cond-mat.dis-nn↗

arXiv2007

Decoherence of a particle in a ring

We consider a particle coupled to a dissipative environment and derive a perturbative formula for the dephasing rate based on the purity of the reduced probability matrix. We apply this formula to the problem of a particle on a ring, that interacts with a dirty metal environment. At low but finite temperatures we find a dephasing rate $\propto T^{3/2}$, and identify dephasing lengths for large and for small rings. These findings shed light on recent Monte Carlo data regarding the effective mass of the particle. At zero temperature we find that spatial fluctuations suppress the possibility of having a power law decay of coherence.

cond-mat.mes-hall↗

arXiv2007

Dephasing of a particle in a dissipative environment

The motion of a particle in a ring of length L is influenced by a dirty metal environment whose fluctuations are characterized by a short correlation distance $\ell << L$. We analyze the induced decoherence process, and compare the results with those obtained in the opposing Caldeira-Leggett limit ($\ell >> L$). A proper definition of the dephasing factor that does not depend on a vague semiclassical picture is employed. Some recent Monte-Carlo results about the effect of finite temperatures on "mass renormalization" in this system are illuminated.

cond-mat.mes-hall↗

arXiv2006

Interference in presence of Dissipation

We study a particle on a ring in presence of various dissipative environments. We develop and solve a variational scheme assuming low frequency dominance. We analyze our solution within a renormalization group (RG) scheme to all orders which reproduces a 2 loop RG for the Caldeira-Legget environment. In the latter case the Aharonov-Bohm (AB) oscillation amplitude is exponential in -R^2 where R is the ring's radius. For either a charge or an electric dipole coupled to a dirty metal we find that the metal induces dissipation, however the AB amplitude is ~ R^{-2} for large R, as for free particles. Cold atoms with a large electric dipole may show a crossover between these two behaviors.

cond-mat.mes-hall↗

arXiv2005

Decoupling and Depinning II: Flux lattices in disordered layered superconductors

Phase transitions of a flux lattice in layered superconductors with magnetic field perpendicular to the layers and in presence of disorder are studied. We find that disorder generates a random Josephson coupling between layers which leads to a Josephson glass (JG) phase at low temperatures; vanishing of the JG order identifies a depinning transition. We also find that disorder and thermal fluctuations lead to layer decoupling where the renormalized Josephson coupling vanishes. Near decoupling an anharmonic regime is found, where usual elasticity and the resulting Bragg glass are not valid. The depinning line crosses the decoupling line at a multicritical point, resulting in three transition lines and a crossover line. The phase diagram is consistent with the unusual data on Bi2Sr2CaCu2O8 such as the "second peak" and depinning transitions. The Josephson plasma frequency is evaluated in the various phases.

cond-mat.supr-con↗

arXiv2005

Decoupling Transition I. Flux Lattices in Pure Layered Superconductors

We study the decoupling transition of flux lattices in a layered superconductors at which the Josephson coupling J is renormalized to zero. We identify the order parameter and related correlations; the latter are shown to decay as a power law in the decoupled phase. Within 2nd order renormalization group we find that the transition is always continuous, in contrast with results of the self consistent harmonic approximation. The critical temperature for weak J is ~1/B, where B is the magnetic field, while for strong J it is~1/sqrt{B} and is strongly enhanced. We show that renormaliztion group can be used to evaluate the Josephson plasma frequency and find that for weak J it is~1/BT^2 in the decoupled phase.

cond-mat.supr-con↗

arXiv2004

Disorder induced transitions in layered Coulomb gases and application to flux lattices in superconductors

A layered system of charges with logarithmic interaction parallel to the layers and random dipoles in each layer is studied via a variational method and an energy rationale. These methods reproduce the known phase diagram for a single layer where charges unbind by increasing either temperature or disorder, as well as a freezing first order transition within the ordered phase. Increasing interlayer coupling leads to successive transitions in which charge rods correlated in N>1 neighboring layers are unbounded by weaker disorder. Increasing disorder leads to transitions between different N phases. The method is applied to flux lattices in layered superconductors in the limit of vanishing Josephson coupling. The unbinding charges are point defects in the flux lattice, i.e. vacancies or interstitials. We show that short range disorder generates random dipoles for these defects. We predict and accurately locate a disorder-induced defect-unbinding transition with loss of superconducting order, upon increase of disorder. While N=1 charges dominate for most system parameters, we propose that in multi-layer superconductors defect rods can be realized.

cond-mat.dis-nn↗

arXiv2004

Antiferromagnetic domain walls in lightly doped layered cuprates

Recent ESR data shows rotation of the antiferromagnetic (AF) easy axis in lightly doped layered cuprates upon lowering the temperature. We account for the ESR data and show that it has significant implications on spin and charge ordering according to the following scenario: In the high temperature phase AF domain walls coincide with (110) twin boundaries of an orthorhombic phase. A magnetic field leads to annihilation of neighboring domain walls resulting in antiphase boundaries. The latter are spin carriers, form ferromagnetic lines and may become charged in the doped system. However, hole ordering at low temperatures favors the (100) orientation, inducing a pi/4 rotation in the AF easy axis. The latter phase has twin boundaries and AF domain walls in (100) planes.

cond-mat.supr-con↗

arXiv2003

Superconductors with broken time-reversal symmetry: Spontaneous magnetization and quantum Hall effects

Broken time reversal symmetry (BTRS) in d+id' as well as in d+is superconductors is studied and is shown to yield current carrying surface states. We evaluate the temperature and thickness dependence of the resulting spontaneous magnetization and show a marked difference between weak and strong BTRS. We also derive the Hall conductance which vanishes at zero wavevector q and finite frequency w, however at finite q,w it has an unusual structure. The chirality of the surface states leads to quantum Hall effects for spin and heat transport in d+id' superconductors.

cond-mat.supr-con↗