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Title: Meissner effect in superconductors with a finite pair momentum

Abstract

The features of the Meissner effect in superconductors with a finite pairing momentum are analyzed. Response to a weak magnetic field is calculated for various cases covering a pair momentum range from q << {delta}/v{sub 0} to q {approx} p{sub 0}, including q = {delta}{sub 0}/v{sub 0} (v{sub 0} is the velocity on the Fermi surface and {delta}{sub 0} is the order parameter at zero temperature; the system of units where {Dirac_h} = 1 is used). The response of a superconductor carrying the transport current at a temperature close to the critical temperature T{sub c} is determined. It is shown that, at a certain critical momentum (current), the response parallel to the momentum vanishes and the London length is infinite. The response perpendicular to the momentum remains unchanged. The response of the superconductor in the current state at zero temperature is calculated. A new contribution to the paramagnetic current is found, and its mechanism is determined. This contribution can be large for high momenta q {approx} p{sub 0}. The Meissner effect is analyzed in detail for the state proposed by Larkin and Ovchinnikov, Zh. Eksp. Teor. Fiz. 47, 1136 (1964) [Sov. Phys. JETP 20, 762 (1964)], as well as bymore » Fulde and Ferrel, Phys. Rev. A 135, 550 (1964). It is shown that the response parallel to the vector q is nonzero and diamagnetic. On the contrary, the response perpendicular to the momentum vanishes at the optimal momentum q{sub 0}. The sensitivity of the Meissner effect to the fine features of the superconducting state such as the quasiparticle spectrum, coherent factors, etc. is demonstrated.« less

Authors:
 [1]
  1. Moscow Engineering Physics Institute (State University) (Russian Federation), E-mail: VEF@supercon.mephi.ru
Publication Date:
OSTI Identifier:
21072471
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Experimental and Theoretical Physics; Journal Volume: 104; Journal Issue: 5; Other Information: DOI: 10.1134/S1063776107050160; Copyright (c) 2007 Nauka/Interperiodica; Article Copyright (c) 2007 Pleiades Publishing, Inc; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; CHARGE TRANSPORT; CRITICAL TEMPERATURE; FERMI LEVEL; MAGNETIC FIELDS; MEISSNER-OCHSENFELD EFFECT; ORDER PARAMETERS; PARAMAGNETISM; SUPERCONDUCTIVITY; SUPERCONDUCTORS

Citation Formats

Elesin, V. F.. Meissner effect in superconductors with a finite pair momentum. United States: N. p., 2007. Web. doi:10.1134/S1063776107050160.
Elesin, V. F.. Meissner effect in superconductors with a finite pair momentum. United States. doi:10.1134/S1063776107050160.
Elesin, V. F.. Tue . "Meissner effect in superconductors with a finite pair momentum". United States. doi:10.1134/S1063776107050160.
@article{osti_21072471,
title = {Meissner effect in superconductors with a finite pair momentum},
author = {Elesin, V. F.},
abstractNote = {The features of the Meissner effect in superconductors with a finite pairing momentum are analyzed. Response to a weak magnetic field is calculated for various cases covering a pair momentum range from q << {delta}/v{sub 0} to q {approx} p{sub 0}, including q = {delta}{sub 0}/v{sub 0} (v{sub 0} is the velocity on the Fermi surface and {delta}{sub 0} is the order parameter at zero temperature; the system of units where {Dirac_h} = 1 is used). The response of a superconductor carrying the transport current at a temperature close to the critical temperature T{sub c} is determined. It is shown that, at a certain critical momentum (current), the response parallel to the momentum vanishes and the London length is infinite. The response perpendicular to the momentum remains unchanged. The response of the superconductor in the current state at zero temperature is calculated. A new contribution to the paramagnetic current is found, and its mechanism is determined. This contribution can be large for high momenta q {approx} p{sub 0}. The Meissner effect is analyzed in detail for the state proposed by Larkin and Ovchinnikov, Zh. Eksp. Teor. Fiz. 47, 1136 (1964) [Sov. Phys. JETP 20, 762 (1964)], as well as by Fulde and Ferrel, Phys. Rev. A 135, 550 (1964). It is shown that the response parallel to the vector q is nonzero and diamagnetic. On the contrary, the response perpendicular to the momentum vanishes at the optimal momentum q{sub 0}. The sensitivity of the Meissner effect to the fine features of the superconducting state such as the quasiparticle spectrum, coherent factors, etc. is demonstrated.},
doi = {10.1134/S1063776107050160},
journal = {Journal of Experimental and Theoretical Physics},
number = 5,
volume = 104,
place = {United States},
year = {Tue May 15 00:00:00 EDT 2007},
month = {Tue May 15 00:00:00 EDT 2007}
}
  • Recently a quite unexpected phenomenon was observed during the study of the magnetic properties of High-T{sub c} superconductors: In the field-cooled regime the magnetic response of some HTSC at very low fields ({le} 1 Oe), instead of being diamagnetic, becomes paramagnetic. Such behavior is perfectly reproducible and stable. This effect is now called the Wohlleben Effect. The samples showing the Wohlleben effect also display anomalous behavior in some other properties (microwave absorption, second harmonic of magnetic susceptibility). In this paper a survey is given of the experimental studies of this and related phenomena, carried out in different laboratories. Corresponding theoreticalmore » models are also discussed. The effect is attributed to the formation of spontaneous currents (spontaneous orbital magnetic moments) in the ground state of the weak link network in case when Josephson coupling between certain grains is negative ({pi}-contacts). Microscopic mechanisms of inverse Josephson coupling are discussed especially in connection with the possible unconventional pairing in HTSC.« less
  • It is generally believed that the laws of thermodynamics govern superconductivity as an equilibrium state of matter, and hence that the normal-superconductor transition in a magnetic field is reversible under ideal conditions. Because eddy currents are generated during the transition as the magnetic flux changes, the transition has to proceed infinitely slowly to generate no entropy. Experiments showed that to a high degree of accuracy no entropy was generated in these transitions. However, in this paper we point out that for the length of times over which these experiments extended, a much higher degree of irreversibility due to decay ofmore » eddy currents should have been detected than was actually observed. We also point out that within the conventional theory of superconductivity no explanation exists for why no Joule heat is generated in the superconductor to normal transition when the supercurrent stops. In addition we point out that within the conventional theory of superconductivity no mechanism exists for the transfer of momentum between the supercurrent and the body as a whole, which is necessary to ensure that the transition in the presence of a magnetic field respects momentum conservation. We propose a solution to all these questions based on the alternative theory of hole superconductivity. The theory proposes that in the normal-superconductor transition there is a flow and backflow of charge in direction perpendicular to the phase boundary when the phase boundary moves. We show that this flow and backflow explains the absence of Joule heat generated by Faraday eddy currents, the absence of Joule heat generated in the process of the supercurrent stopping, and the reversible transfer of momentum between the supercurrent and the body, provided the current carriers in the normal state are holes. - Highlights: • The normal-superconductor phase transition is reversible. • Within the conventional theory, Foucault currents give rise to irreversibility. • To suppress Foucault currents, charge has to flow in direction perpendicular to the phase boundary. • The charge carriers have to be holes. • This solves also the angular momentum puzzle associated with the Meissner effect.« less
  • We have studied the low-field Meissner effect of polycrystalline Bi high-temperature superconductors using a special superconducting-quantum-interference-device magnetometer. In certain samples a surprising feature was observed: Instead of the usual diamagnetic moment a paramagnetic moment develops in the field cooling mode below [ital T][sub [ital c]] for fields [ital H][lt]1 Oe. The data are consistent with orbital paramagnetic moments due to spontaneous currents. Such currents may originate in so-called [pi] contacts in the weak-link network of polycrystalline material. In some of these samples also an anomaly in the low-field microwave absorption was observed, which is obviously correlated with the existence ofmore » spontaneous currents.« less
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