Renormalization of electron-phonon coupling in the Mott-Ioffe-Regel limit due to point defects in the V_1-x Ti _x alloy...

We report here the temperature dependence of electrical resistivity ([Formula: see text](T)), heat capacity (C(T)) and thermal conductivity ([Formula: see text](T)) of superconducting V_1-x Ti _x alloys in the absence and presence of external applied magnetic fields. The [Formula: see text](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 ([Formula: see text]) indicates that these alloys are in the intermediate coupling limit. The [Formula: see text](T) increases in certain V_1-x Ti _x alloys as the temperature decreases below the [Formula: see text] 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.