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K. V. Samokhin

Publications and source records attributed to K. V. Samokhin.

66 records · Page 4Linked to original sources
arXiv2002

Possible symmetries of the superconducting order parameter in a hexagonal ferromagnet

We study the order parameter symmetry in a hexagonal crystal with co-existing superconductivity and ferromagnetism. An experimental example is provided by carbon-based materials, such as graphite-sulfur composites, in which an evidence of such co-existence has been recently discovered. The presence of a non-zero magnetization in the normal phase brings about considerable changes in the symmetry classification of superconducting states, compared to the non-magnetic case.

cond-mat.supr-con↗
arXiv2002

Order parameter symmetry in ferromagnetic superconductors

We analyze the symmetry and the nodal structure of the superconducting order parameter in a cubic ferromagnet, such as ZrZn$_2$. We demonstrate how the order parameter symmetry evolves when the electromagnetic interaction of the conduction electrons with the internal magnetic induction and the spin-orbit coupling are taken into account. These interactions break the cubic symmetry and lift the degeneracy of the order parameter. It is shown that the order parameter which appears immediately below the critical temperature has two components, and its symmetry is described by {\em co-representations} of the magnetic point groups. This allows us to make predictions about the location of the gap nodes.

cond-mat.supr-con↗
arXiv2002

A Model for Superconductivity in Ferromagnetic ZrZn2

This article proposes that superconductivity in the ferromagnetic state of ZrZn$_2$ is stabilized by an exchange-type interaction between the magnetic moments of triplet-state Cooper pairs and the ferromagnetic magnetization density. This explains why superconductivity occurs in the ferromagnetic state only, and why it persists deep into the ferromagnetic state. The model of this article also yields a particular order parameter symmetry, which is a prediction that can be checked experimentally.

cond-mat.supr-con↗
arXiv2002

Symmetry of the order parameter in superconducting ZrZn_2

We apply symmetry considerations to study the possible superconducting order parameters in ferromagnetic ZrZn_2. We predict that the presence and the location of the superconducting gap nodes depend on the direction of magnetization M. In particular, if M is directed along the z axis, then the order parameter should always have zeros. We also discuss how to determine the gap symmetry in ZrZn_2 using ultrasound attenuation measurements.

cond-mat.supr-con↗
arXiv2001

Electron-Phonon Interaction and Ultrasonic Attenuation in the Ruthenate and Cuprate superconductors

This article derives an electron-phonon interaction suitable for interpreting ultrasonic attenuation measurements in the ruthenate and cuprate superconductors. The huge anisotropy found experimentally (Lupien et al., 2001) in Sr2RuO4 in the normal state is accounted for in terms of the layered square-lattice structure of Sr2RuO4, and the dominant contribution to the attenuation in Sr2RuO4 is found to be due to electrons in the gamma band. The experimental data in the superconducting state is found to be inconsistent with vertical lines nodes in the gap in either (100) or (110) planes. Also, a general method, based on the use of symmetry, is developed to allow for the analysis of ultrasonic attenuation experiments in superconductors in which the electronic band structure is complicated or not known. Our results, both for the normal-state anisotropy, and relating to the positions of the gap nodes in the superconducting state, are different from those obtained from analyses using a more traditional model for the electron-phonon interaction in terms of an isotropic electron stress tensor. Also, a brief discussion of the ultrasonic attenuation in UPt3 is given.

cond-mat.supr-con↗
arXiv2001

Localized surface states in HTSC: Alternative mechanism of zero-bias conductance peaks

It is shown that the quasiparticle states localized in the vicinity of surface imperfections of atomic size can be responsible for the zero-bias tunneling conductance peaks in high-Tc superconductors. The contribution from these states can be easily separated from other mechanisms using their qualitatively different response on an external magnetic field.

cond-mat.supr-con↗
arXiv2001

Effect of magnetic field on impurity bound states in high-temperature superconductors

We consider the influence of a magnetic field H on the quasiparticle bound states near scalar impurities in d-wave superconductors. A ``Doppler shift'' in the excitation energies induced by the supercurrent leads to several important effects. At large but finite impurity strength, there are corrections to the energy and width of the impurity-induced resonance, proportional to H^2. On the other hand, in the limit of very strong impurity potential (unitary limit), the bound state is destroyed and acquires a finite width proportional to H/ln H. There are also considerable changes in the asymptotic behaviour of the bound state wave functions.

cond-mat.supr-con↗
arXiv2000

Spin-orbit coupling in interacting quasi-one-dimensional electron systems

We present a new model for the study of spin-orbit coupling in interacting quasi-one-dimensional systems and solve it exactly to find the spectral properties of such systems. We show that the combination of spin-orbit coupling and electron-electron interactions results in: the replacement of separate spin and charge excitations with two new kinds of bosonic mixed-spin-charge excitation, and a characteristic modification of the spectral function and single-particle density of states. Our results show how manipulation of the spin-orbit coupling, with external electric fields, can be used for the experimental determination of microscopic interaction parameters in quantum wires.

cond-mat.mes-hall↗
arXiv1999

Field theory of self-avoiding walks in random media

Based on the analogy with the quantum mechanics of a particle propagating in a {\em complex} potential, we develop a field-theoretical description of the statistical properties of a self-avoiding polymer chain in a random environment. We show that the account of the non-Hermiticity of the quantum Hamiltonian results in a qualitatively different structure of the effective action, compared to previous studies. Applying the renormalisation group analysis, we find a transition between the weak-disorder regime, where the quenched randomness is irrelevant, and the strong-disorder regime, where the polymer chain collapses. However, the fact that the renormalised interaction constants and the chiral symmetry breaking regularisation parameter flow towards strong coupling raises questions about the applicability of the perturbative analysis.

cond-mat.stat-mech↗
arXiv1999

Persistent current in a mesoscopic ring with diffuse surface scattering

The persistent current in a clean mesoscopic ring with ballistic electron motion is calculated. The particle dynamics inside a ring is assumed to be chaotic due to scattering at the surface irregularities of atomic size. This allows one to use the so-called ``ballistic'' supersymmetric σmodel for calculation of the two-level correlation function in the presence of a nonzero magnetic flux.

cond-mat.mes-hall↗
arXiv1997

Dynamical scaling at the quantum Hall transition: Coulomb blockade versus phase breaking

We argue that the finite temperature dynamics of the integer quantum Hall system is governed by two independent length scales. The consistent scaling description of the transition makes crucial use of two temperature critical exponents, reflecting the interplay between charging effects and interaction-induced dephasing. Experimental implications of the two-scale picture are discussed.

cond-mat.mes-hall↗