Anisotropics-wave superconductivity in borocarbidesLuNi2B2Cand

Kazumi Maki

¹

,

Peter Thalmeier

²

,

Hyung Jin Won

³

Abstract

The symmetry of superconductivity in borocarbides LuNi2B2C and YNi2B2C is an outstanding issue. Here an anisotropic s-wave order parameter (or s+g model) is proposed for LuNi2B2C and YNi2B2C . In spite of the dominant s-wave component the present superconducting order parameter ∆(k) has nodes and gives rise to the √ H dependent specific heat in the vortex state (the Volovik effect). This model predicts the fourfold symmetry both in the angular dependent thermal conductivity and in the excess Dingle temperature in the vortex state, which should be readily accessible experimentally.

Gap symmetry of superconducting borocarbide YNi2B2C and skutterudite PrOs4Sb12

“…We note that first of all the angular dependence of κ zz is given by I(θ, φ) which is fully confirmed in [8]. The details of the above expressions are different from those given previously [9,10] due to the present more realistic treatment of the impurity scattering in the s+g wave case. On the other hand the conclusion that a gap ω g Γ opens immediately for s+g wave order parameter makes it now hard to understand the H linear dependence of thermal conductivity at lowest temperatures reported in [42].…”

“…More recently the magnetothermal conductivity data from YNi 2 B 2 C and PrOs 4 Sb 12 has revealed the presence of point nodes in ∆(k) [8,11]. These order parameters are described in terms of s+g wave gap functions [9,10,12]. This is the first time such hybrid gap functions consisting of a superposition of representations have been found.…”

“…Due to their tetragonal space group I4/mmm the borocarbides have fourfold rotational symmetry within the a-b plane. The simplest ∆(k) which satisfies these constraints appears to be s+g-wave superconductor [8,9] …”

“…Indeed Izawa et al have shown f-wave sc in Sr 2 RuO 4 [5], d-wave sc in CeCoIn 5 [6] and κ-(ET) 2 Cu(NCS) 2 [7] through the angle dependent magnetothermal conductivity. More recently gap functions ∆(k) in borocarbide YNi 2 B 2 C and skutterudite PrOs 4 Sb 12 are shown to have point nodes and described in terms of s+g-wave sc [8][9][10][11][12]. We show |∆(k)| of these superconductors in Fig.…”

The Properties of the Superconducting State in YNi2B2C: The One-Band Eliashberg Approach

“…In particular, the dependence of the upper critical field (H C2 ) on the temperature [11,12] or the results obtained with a use of the directional point-contact spectroscopy [13,14] suggest the necessity of the two-band model being used. On the other hand, some researchers basing on the thermal and spectroscopic experiments are moving toward the direction of the one-band models with a non-trivial wave symmetry (s + g or even d-wave symmetry) [15][16][17][18]. The issue is clouding by the fact that the calculations conducted till the present day for the one-band Eliashberg model were (863) not strict; the studies were based on very simplified form of the Eliashberg function [19] or approximated analytical formulae [20].…”