arXiv subjects

M. V. Feigelman

Publications and source records attributed to M. V. Feigelman.

15 recordsLinked to original sources

arXiv2021

Conductivity and thermoelectric coefficients of doped SrTiO$_3$ at high temperatures

We developed a theory of electric and thermoelectric conductivity of lightly doped SrTiO$_3$ in the non-degenerate region $k_B T \geq E_F$, assuming that the major source of electron scattering is their interaction with soft transverse optical phonons present due to proximity to ferroelectric transition. We have used kinetic equation approach within relaxation-time approximation and we have determined energy-dependent transport relaxation time $τ(E)$ by the iterative procedure. Using electron effective mass $m$ and electron-transverse phonon coupling constant $λ$ as two fitting parameters, we are able to describe quantitatively a large set of the measured temperature dependences of resistivity $R(T)$ and Seebeck coefficient $\mathcal{S}(T)$ for a broad range of electron densities studied experimentally in recent paper [1]. In addition, we calculated Nernst ratio $ν=N/B$ in the linear approximation over weak magnetic field in the same temperature range.

cond-mat.other↗

arXiv2018

Cooper pair splitting in diffusive magnetic SQUIDs

We study Josephson junctions with weak links consisting of two parallel disordered arms with magnetic properties -- ferromagnetic, half-metallic or normal with magnetic impurities. In the case of long links, the Josephson effect is dominated by mesoscopic fluctuations. In this regime, the system realises a $φ_0$ junction with sample-dependent $φ_0$ and critical current. Cooper pair splitting between the two arms plays a major role and leads to $2Φ_0$ periodicity of the current as a function of flux between the arms. We calculate the current and its flux and polarization dependence for the three types of magnetic links.

cond-mat.mes-hall↗

arXiv2015

Josephson current between topological and conventional superconductors

We study the stationary Josephson current in a junction between a topological and an ordinary (topologically trivial) superconductor. Such an S-TS junction hosts a Majorana zero mode that significantly influences the current-phase relation. The presence of the Majorana state is intimately related with the breaking of the time-reversal symmetry in the system. We derive a general expression for the supercurrent for a class of short topological junctions in terms of the normal state scattering matrix. The result is strongly asymmetric with respect to the superconducting gaps in the ordinary ($Δ_0$) and topological ($Δ_{\mathrm{top}}$) leads. We apply the general result to a simple model of a nanowire setup with strong spin-orbit coupling in an external magnetic field and proximity-induced superconductivity. The system shows parametrically strong suppression of the critical current $I_c \propto Δ_{\mathrm{top}}/R_N^2$ in the tunneling limit ($R_N$ is the normal state resistance). This is in strong contrast with the Ambegaokar-Baratoff relation applicable to junctions with preserved time-reversal symmetry. We also consider the case of a generic junction with a random scattering matrix and obtain a more conventional scaling law $I_c \propto Δ_{\mathrm{top}}/R_N$.

cond-mat.mes-hall↗

arXiv2013

Electron-Electron Interactions and Plasmon Dispersion in Graphene

Plasmons in two-dimensional electron systems with nonparabolic bands, such as graphene, feature strong dependence on electron-electron interactions. We use a many-body approach to relate plasmon dispersion at long wavelengths to Landau Fermi-liquid interactions and quasiparticle velocity. An identical renormalization is shown to arise for the magnetoplasmon resonance. For a model with N>>1 fermion species, this approach predicts a power-law dependence for plasmon frequency vs. carrier concentration, valid in a wide range of doping densities, both high and low. Gate tunability of plasmons in graphene can be exploited to directly probe the effects of electron-electron interaction.

cond-mat.mes-hall↗

arXiv2010

Dynamic susceptibility of a spin ice near the critical point

We consider spin ice magnets (primarily, $\mathrm{Dy_2Ti_2O_7}$) in the vicinity of their critical point on the $(H,T)$ plane. We find that the longitudinal susceptibility diverges at the critical point, leading to the behaviour qualitatively similar to the one which would result from non-zero conductance of magnetic charges. We show that dynamics of critical fluctuations belongs to the universality class of easy-axis ferroelectric and calculate logarithmic corrections (within two-loop approximation) to the mean-field critical behavior.

cond-mat.other↗

arXiv2008

Inelastic cotunneling through a long diffusive wire

We show that electron transport through a long multichannel wire, connected to leads by tunnel junctions, at low temperatures and voltages is dominated by inelastic cotunnelling. This mechanism results in experimentally observed power-law dependence of conductance on temperature and voltage, in the diffusive regime where usual Coulomb anomaly theory leads to exponentially low conductance. The power-law exponent is proportional to the distance between contacts.

cond-mat.mes-hall↗

arXiv2002

Ground-state properties of the Rokhsar-Kivelson dimer model on the triangular lattice

We explicitly show that the Rokhsar-Kivelson dimer model on the triangular lattice is a liquid with topological order. Using the Pfaffian technique, we prove that the difference in local properties between the two topologically degenerate ground states on the cylinders and on the tori decreases exponentially with the system size. We compute the relevant correlation length and show that it equals the correlation length of the vison operator.

cond-mat.str-el↗

arXiv2002

Weak Charge Quantization on Superconducting Islands

We consider the Coulomb blockade on a superconductive quantum dot strongly coupled to a lead through a tunnelling barrier and/or normal diffusive metal. Andreev transport of the correlated pairs leads to quantum fluctuations of the charge on the dot. These fluctuations result in exponential renormalization of the effective charging energy. We employ two complimentary ways to approach the problem, leading to the coinciding results: the instanton and the functional RG treatment of the non-linear sigma model. We also derive the charging energy renormalization in terms of arbitrary transmission matrix of the multi-channel interface.

cond-mat.mes-hall↗

arXiv1999

Quiet SDS Josephson Junctions for Quantum Computing

Unconventional superconductors exhibit an order parameter symmetry lower than the symmetry of the underlying crystal lattice. Recent phase sensitive experiments on YBCO single crystals have established the d-wave nature of the cuprate materials, thus identifying unambiguously the first unconventional superconductor. The sign change in the order parameter can be exploited to construct a new type of s-wave - d-wave - s-wave Josephson junction exhibiting a degenerate ground state and a double-periodic current-phase characteristic. Here we discuss how to make use of these special junction characteristics in the construction of a quantum computer. Combining such junctions together with a usual s-wave link into a SQUID loop we obtain what we call a `quiet' qubit --- a solid state implementation of a quantum bit which remains optimally isolated from its environment.

cond-mat.mes-hall↗

arXiv1997

History-Dependence and Ageing in a Periodic Long-Range Josephson Array

History-dependence and ageing are studied in the low-temperature glass phase of a long-range periodic Josephson array. This model is characterized by two parameters, the number of wires ($2N$) and the flux per unit strip ($α$); in the limit $N \to \infty$ and fixed $α\ll 1$ the dynamics of the model are described by the set of coupled integral equations, which coincide with those for the $p=4$ disordered spherical model. Below the glass transition we have solved these equations numerically in a number of different regimes. We observe power-law ageing after a fast quench with an exponent that decreases rapidly with temperature. After slow cooling to a not-too-low temperature, we see ageing characterized by the appearance of a new time scale which has a power law dependence on the cooling rate. By contrast if the array is cooled slowly to very low temperatures the ageing disappears. The physical consequences of these results in different cooling regimes are discussed for future experiment. We also study the structure of the phase space in the low temperature glassy regime. Analytically we expect an exponential number of metastable states just below the glass transition temperature with vanishing mutual overlap, and numerical results indicate that this scenario remains valid down to zero temperature. Thus in this array there is no further subdivision of metastable states. We also investigate the probability to evolve to different states given a starting overlap, and our results suggest a broad distribution of barriers.

cond-mat.dis-nn↗

arXiv1996

An Experimentally Realizable Weiss Model for Disorder-Free Glassiness

We summarize recent work on a frustrated periodic long-range Josephson array in a parameter regime where its dynamical behavior is identical to that of the $p=4$ disordered spherical model. We also discuss the physical requirements imposed by the theory on the experimental realization of this superconducting network.

cond-mat.dis-nn↗

arXiv1995

Glass Formation in a Periodic Long-Range Josephson Array

We present an analytic study of a dynamical instability in a periodic long-range Josephson array frustrated by a weak transverse field. This glass transition is characterized by a diverging relaxation time and a jump in the Edwards-Anderson order parameter; it is {\sl not} accompanied by a coinciding static transition.

cond-mat↗

arXiv1995

Slow cooling dynamics of the Ising $p$-spin interaction spin-glass model

We have studied dynamical behaviour of the infinite-range Ising spin glass model with $p$-spin interaction above and below the transition into the non-ergodic phase. The transition is continuous at sufficiently high external magnetic field. The dynamic critical exponent of the power-law decay of the autocorrelation function at the transition point is shown to decrease smoothly to zero as the field approaches the ``tricritical'' point from above; at lower fields the transition is discontinuous. The {\it slow cooling} approach is used to study the nonergodic behavior below the transition at zero external field. It is shown that the anomalous response function $Δ(t,t')$ contains $δ$-function as well as regular contributions at {\it any} temperature below the phase transition. No evidence of the second phase transition (known to exist within the static replica solution of the same model) is found. At lower enough temperatures the {\it slow cooling} solution approaches the one known for the standard SK model.

cond-mat↗

arXiv1994

Non local screening in a vortex line liquid

We show that the recent experiments \cite{safar} reporting the onset of the non-local conductivity in the vortex state of $YBaCuO$ single crystals indicate the presence of a new liquid phase of vortices. This phase is intermediate between the normal metal and the Abrikosov lattice. We use the mapping of the vortex problem to the problem of bose liquid to determine theoretically the properties of the proposed vortex liquid phase and compare them with the data.

cond-mat↗

arXiv1994

On the theory of diamagnetism in granular superconductors

We study a highly disordered network of superconducting granules linked by weak Josephson junctions in magnetic field and develop a mean field theory for this problem. The diamagnetic response to a slow {\it variations} of magnetic field is found to be analogous to the response of a type-II superconductor with extremely strong pinning. We calculate an effective penetration depth $λ_g$ and critical current $j_c$ and find that both $λ_g^{-1}$ and $j_c$ are non-zero but are strongly suppressed by frustration.

cond-mat↗