Field dependence of the zero-energy density of states around vortices in an anisotropic-gap superconductor

It is shown theoretically that the Sommerfeld coefficient gamma(B) in the mixed state contains useful information on the gap topology in a superconductor. We accurately evaluate gamma(B) against magnetic induction B by using microscopic quasiclassical theory. The linear portion in gamma(proportional toB) relative to B-c2 and its slope in low field faithfully corresponds to the gap anisotropy, so that we can distinguish the nodal gap and the anisotropic full gap, and estimate the magnitude of the gap anisotropy.