Josephson effect in a weak link between borocarbides

Abstract

A stationary Josephson effect is analyzed theoretically for a weak link between borocarbide superconductors. It is shown that different models of the order parameter result in qualitatively different current-phase relations. PACS: 74.50.+rDetermination of the symmetry of the order parameter D in novel unconventional superconductors is important for the development of modern physics of superconductivity because the dependence of D( ) k on the direction of the electron wave vector k on the Fermi surface determines all of the kinetic and thermodynamic characteristics of the superconductor. Calculation of the order parameter D( ) k is a fundamental problem and requires knowledge of the pairing potential. Some general information about D( ) k can be obtained from the symmetry of a normal state, i.e., according to the Landau theory of secon-order phase transitions [1], the order parameter transforms only accoding to irreducible representations of the symmetry group of the normal state (for review, see [2]). Nevertheless, symmetry considerations reserve for the order parameter considerable freedom in the selection of irreducible representation and its basis functions. Therefore in many papers authors consider different models of the order parameter, which are based on possible representations of crystallographic point groups. The subsequent comparison of theoretical results with experimental data makes it possible to choose between available models of the order parameter. The Josephson effect in superconducting weak links is one of the most suitable instruments for investigation of the symmetry of D( ) k . It has heen shown, for example, that current-phase relations j J ( ) j in unconventional superconductors are quite different for different models of D( ) k , and hence the study of the Josephson effect enables one to judge the applicability of different models to the novel superconductors [3].Borocarbides, such as YNi 2 B 2 C and LuNi 2 B 2 C, exhibit unconventional superconductivity. There is strong evidence that in these materials the order parameter is highly anisotropic [4]. The order parameter in these compounds has fourfold symmetry, and there are deep minima along the [100] and [010] directions [4,5]. Both the symmetry of the borocarbide crystal structure and the experimental results have allowed the authors of Refs.[6] to suggest an s g + -wave model of the order parameter to describe the superconductivity in the borocarbides: J j is an alternating-sign quantity, which means that some reflected trajectories experience the intrinsic phase difference. This result in the suppression of the order parameter in the vicinity of the interface between two superconductors similar to what is known about the contact of two d-wave superconductors (see [7] and references therein); and in this case the non-self-consistent calculation, presented below, can be justified for the weak links in the form of both the point contact and the plane boundary between two banks. Another consequence of the intrinsic phase difference is th...

Proximity and Josephson effects in microstructures based on multiband superconductors (Review Article)

“…It should be noted that, among other things, interest in the studies of the Josephson effect is due to the fact that phase-sensitive techniques often provide the most valuable information on the symmetry of the order parameter in unusual superconductors and are a sufficiently productive "tool" for identifying it in compounds where this problem remains unsolved (see, e.g., Refs. [45][46][47][48].…”