Superconducting Transition Temperature of 2H−TaS2 Intercalation Compounds Determined by the Phonon Spectrum

Abstract

The specific heat in the normal and superconducting states of single-crystal intercalation compounds of the host material 2H−TaS2 was measured from 1.7 to 9 K by use of a thermal relaxation method. By studying two extreme cases of charge transfer n, namely the 9 A methylene blue intercalation compound (9 A MB+−TaS2) (n = 0.06) and K0.33TaS2 (n = 0.33), and comparing the results with literature data, it is seen that charge transfer has only minor influence on the electronic specific heat in the normal state. This is in drastic contradiction to the expectation from a rigid band model. The contribution of the phonon-parameter β, however, varies with intercalation. No direct correspondence between Tc and the Debye temperature θD can be seen, but if θD is multiplied by a factor, characterizing the intercalation compound, scaling between Tc and the corrected Debye temperature is found. Furthermore, it is observed that the superconducting transition temperature of the methylene blue intercalation compound is sen...