Theory of gap-node detection by angle-resolved specific heat measurement

The specific heat oscillation in the mixed state of type II superconductors is studied theoretically when rotating a field within a plane containing a gap minimum and maximum. The calculations are performed microscopically by solving the quasi-classical Eilenberger equation for vortex lattices. The field dependence of the oscillation amplitude can discriminate between the nodal and anisotropic gap with a finite minimum and the oscillation phase gives the gap minimum position on the Fermi surface. These also provide a way to separate out the anisotropic behaviour due to the Fermi velocity.