arXiv subjects

Boris Z. Spivak

Publications and source records attributed to Boris Z. Spivak.

6 recordsLinked to original sources

arXiv2025

Low-temperature dissipative conductivity of superconductors with paramagnetic impurities

In s-wave superconductors with a small concentration of magnetic impurities, the only electronic excitations that remain available at low temperatures are the excitations of the system of localized spins. We discuss a new mechanism of interaction between electromagnetic waves and the localized spins in disordered superconductors. A supercurrent induces randomly distributed spin density of the itinerant electrons, which couples to the impurity spins by exchange interaction. Acceleration of the Cooper pair condensate by the external AC electric field of frequency $ω$ creates a strong, time-dependent exchange field acting on the localized spins, which is inversely proportional to $ω$. As a result, the low-frequency dissipative part of the conductivity saturates to a nonzero value. We use the fluctuation-dissipation theorem to evaluate the spectrum of equilibrium current fluctuations associated with the fluctuation in the spin subsystem. We also predict that in the presence of a DC magnetic field parallel to the superconducting film, the system of spins exhibits a large positive magnetoconductance.

cond-mat.supr-con↗

arXiv2022

Strange-metal behavior in a Fermi liquid with strange scatterers

A variety of low-temperature, normal-state properties of optimally and overdoped cuprate superconductors, including the DC and optical transport responses, are sufficiently anomalous that they might seem to be inconsistent with any quasiparticle description. However, we show by explicit construction that the most salient phenomena can be accounted for in a system with localized "strange scatterers" embedded into a Fermi liquid with a conventional quasiparticle description. Such scatterers could originate from "two-level systems" associated with an electronic glassy state with short-range charge-order correlations.

cond-mat.str-el↗

arXiv2021

Incoherent Excitation of Coherent Higgs Oscillations in Superconductors

We investigate theoretically the excitation of Higgs oscillations of the order parameter in superconductors by incoherent short pulses of light with frequency much larger than the superconducting gap. The excitation amplitude of the Higgs mode is controlled by a single parameter which is determined by the total number of quasiparticles excited by the pulse. This fact can be traced back to the universality of the shape of the light-induced quasiparticle cascade at energy below the Debye frequency and above the gap.

cond-mat.supr-con↗

arXiv2018

Magnetoenhancement of superconductivity in composite D-wave superconductors

We study composite D-wave superconductors consisting of randomly oriented and randomly distributed superconducting droplets embedded into a matrix. In a certain range of parameters the application of a small magnetic field enhances the superconductivity in these materials while larger fields suppress superconductivity as usual in conventional superconductors. We investigate the magnetic field dependence of the superfluid density and the critical temperature of such superconductors.

cond-mat.supr-con↗

arXiv2018

Theory of combustion in disordered media

The conventional theory of combustion describes systems where all of the parameters are spatially homogeneous. On the other hand, combustion in disordered explosives has long been known to occur after local regions of the material, called "hot spots", are ignited. In this article we show that a system of randomly distributed hot spots exhibits a dynamic phase transition, which, depending on parameters of the system can be either first or second order. These two regimes are separated by a tri-critical point. We also show that on the qualitative level the phase diagram of the system is universal. It is valid in two and three dimensions, in the cases when the hot spots interact either by heat or sound waves and in a broad range of microscopic disorder models.

cond-mat.dis-nn↗

arXiv2017

Theory of deflagration in disordered media

The conventional theory of burning works well in the case of uniform media where all system parameters are spatially independent. We develop a theory of burning in disordered media. In this case, rare regions (hot spots) where the burning process is more effective than on average may control the heat propagation in an explosive sample. We show that most predictions of the theory of burning are quite different from the conventional case. In particular, we show that a system of randomly distributed hot spots exhibits a dynamic phase transition, which is similar to the percolation transition. Depending on parameters of the system the phase transition can be either first or second order. These two regimes are separated by a tricritical point. The above results may be applicable to dynamics of any over-heated disordered system with a first order phase transition.

cond-mat.stat-mech↗