Impurity effects of hydrogen and deuterium in vanadium nanoconstrictions

To study non-magnetic and magnetic impurity effects at the superconductor-normal metal interfaces, we have measured the differential conductance dI/dV for Josephson contacts made by vanadium (V) nanoconstrictions with a different amount of hydrogen (H) and deuterium (D) impurities, which are prepared by a mechanically controllable break junction (MCBJ) technique at low temperature. Below the superconducting transition temperature T _C, we have found distinct peaks within and outside the gap, known as the sub-gap structure and an over-The-gap structure respectively, due to 5% concentration of atomic H and D on V nanocontact. Moreover, the temperature dependence of dI/dV spectra represents that both structures are survived until the critical temperature T _C, which is consistent with the prediction of BCS energy gap. On the other hand, a very high concentrating phase (30atom%) behaves as a normal metal.