Renormalization of electron–phonon coupling in the Mott–Ioffe–Regel limit due to point defects in the V1−xTix alloy superconductors

Abstract

We report here the temperature dependence of electrical resistivity ((T)), heat capacity (C(T)) and thermal conductivity ((T)) of superconducting V1−xTix alloys in the absence and presence of external applied magnetic fields. The (T) changes from positive temperature coefficient of resistivity (TCR) to negative TCR at about x = 0.7 indicating that many of these alloys lie close to the Mott–Ioffe–Regel (MIR) limit. The jump in the C(T) across the superconducting transition temperature () indicates that these alloys are in the intermediate coupling limit. The (T) increases in certain V1−xTix alloys as the temperature decreases below the indicating that the phonons dominate the heat conduction in the superconducting state, whereas we found that the electrons are the major carriers of heat in the normal state. Our analysis suggests that the unusual features of thermal conductivity have origin in (i) the electron mean free path approaching the inter atomic distances (MIR limit) and (ii) the renormalization of the phonon mean free path due to the presence of point defects and the electron–phonon interaction.