Quasi-Classical Calculation of the Mixed-State Thermal Conductivity in s- and d-Wave Superconductors

To see how superconducting gap structures affect the longitudinal component of mixed-state thermal conductivity kappaₓₓ(B), the magnetic-field dependences of kappaₓₓ(B) in s-wave and d-wave superconductors are investigated. Calculations are performed on the basis of the quasi-classical theory of superconductivity by fully taking account of the spatial variation of the normal Green's function, neglected in previous works, by the Brandt-Pesch-Tewordt approximation. On the basis of our result, we discuss the possibility of kappaₓₓ(B) measurement as a method of probing the gap structure.