Effect of nonstoichiometry on the superconductivity of PdTe

Transition metal chalcogenides are known to exhibit exciting physical properties such as unconventional superconductivity and unusual magnetism. We have found that stoichiometric PdTe displays unconventional superconducting properties below 4.5 K. The application of either external or internal pressure tends to decrease the superconducting transition temperature T_c. One way to create the positive internal pressure is to create nonstoichiometric Pd_1-xTe. With 5% Pd deficiency (x ~ 0.05), T_c drops to half. While the unit cell volume reduces, the Debye temperature obtained from the specific heat increases with decreasing T_c. Such a trend cannot be understood in the framework of the BCS theory, when the variation of the density of states and electron-phonon coupling are considered. The implications will be discussed.