Theory of extracting superconducting gap structure from field-angle rotational experiments

Abstract

We study the relation between the superconducting gap structure and field-orientational dependence of zero-energy density of states (ZEDOS), on the basis of an approximate analytical solution of the Eilenberger equation. Firstly, we quantitatively estimate the crossover magnetic field below which the result of the Doppler-shift method becomes correct. Secondly, we show that field-orientational dependence of ZEDOS has rather broad minima when the shape of node is point-like, in contrast to the result of the Doppler-shift method. Finally, we propose a novel mechanism leading to the cusp-like minima found in YNi 2 B 2 C in terms of a two-band model. This two-band model also provides a typical example in which the Doppler-shift predominant region is suppressed to much lower fields.