Effects of Fermi surface and superconducting gap structure in field-rotational experiments: A possible explanation for the cusplike singularity in YNi2B2C

Abstract

We have studied the field-orientational dependence of the zero-energy density of states (FODOS) for a series of systems with different Fermi surface and superconducting gap structures. Instead of the phenomenological Doppler-shift method, we use an approximate analytical solution of the Eilenberger equation together with self-consistent determination of the order parameter and a variational treatment of the vortex lattice. First, we compare the zero-energy density of states when a magnetic field is applied in the nodal direction [νnode(0)] and in the antinodal direction [νanti(0)], by taking account of the field-angle dependence of the order parameter. As a result, we found that there exists a crossover magnetic field H* so that νanti(0)>νnode(0) for H<H*, while νnode(0)>νanti(0) for H>H*, consistent with our previous analyses. Next, we showed that H* and the shape of the FODOS are determined by a contribution from the small part of the Fermi surface where the Fermi velocity is parallel to the field-rotational plane. In particular, we found that H* is lowered and the FODOS has broader minima when a superconducting gap has point nodes, in contrast to the result of the Doppler-shift method. We also studied the effects of in-plane anisotropy of the Fermi surface. We found that the in-plane anisotropy of a quasi-two-dimensional Fermi surface sometimes becomes larger than the effects of the Doppler shift and can destroy the Doppler-shift-predominant region. In particular, this tendency is strong in a multiband system where superconducting coherence lengths are isotropic. Finally, we addressed the problem of the cusplike singularity in YNi2B2C and present a possible explanation of this phenomenon.

Source-reported materials — not catalogue approval

Similar papers