Study of the superconducting gap inRNi2B2C(R=

Abstract

Superconductivity-induced changes in the electronic Raman scattering response were observed for the RNi 2 B 2 C (R = Y, Lu) system in different scattering geometries. In the superconducting state, 2∆-like peaks were observed in A 1g , B 1g , and B 2g spectra from single crystals. The peaks in A 1g and B 2g symmetries are significantly sharper and stronger than the peak in B 1g symmetry. The temperature dependence of the frequencies of the 2∆-like peaks shows typical BCS-type behavior, but the apparent values of the 2∆ gap are strongly anisotropic for both systems. In addition, for both YNi 2 B 2 C and LuNi 2 B 2 C systems, there exists reproducible scattering strength below the 2∆ gap which is roughly linear to the frequency in B 1g and B 2g symmetries.This discovery of scattering below the gap in non-magnetic borocarbide superconductors, which are thought to be conventional BCS-type superconductors, 1 is a challenge for current understanding of superconductivity in this system.

Highly Anisotropic Gap Function in Borocarbide SuperconductorLuNi2B2C

“…It has generally been thought that these materials are described by an order parameter with s-wave symmetry and pairing which proceeds via the electron-phonon coupling [7][8][9]. However, there is recent evidence for low-energy excitations in the superconducting state, whether from the anomalous field dependence of the specific heat [10,11] and the microwave surface impedance [11,12], or from the presence of scattering below the gap in Raman measurements [13]. This has been interpreted in terms of an anisotropic s-wave gap [10,11] (see also reference [14]).…”

Evidence for Nodal Quasiparticles in the Nonmagnetic SuperconductorYNi2B2Cvia Field-Angle-Dependent Heat Capacity

“…The rare earth borocarbide superconductors RNi 2 B 2 C (R=Y, Lu, Tm, Er, Ho, and Dy) had been generally thought to exhibit isotropic s-wave pairing via electron-phonon coupling [5,6,7,8,9], but there is growing evidence that the gap function is highly anisotropic or has a nodal structure on the momentum surface [4,10,11,12,13,14]. In specific heat measurements, a power law behavior was observed in the temperature dependence and the electronic coefficient γ(H), to the extent it can be extracted, follows a square-root field dependence [10,15].…”

BCS theory fors+g-wave superconductivity in borocarbidesY(Lu)Ni2Yuan1, Thalmeier2 2003Phys. Rev. B180150View full textAdd to dashboardCite

“…Under these interaction parameters, ∆(T ) and x(T ) are calculated self-consistently from Eqs. (9) and (10). The results are shown by the solid lines in Fig.…”

“…In this case the pure s-and g-wave are no longer solutions of Eqs. (9) and (10). Furthermore only one stable s+g solution is present.…”