Effect of spin fluctuations on tunneling conductance in diffusive normal metal/conventional superconductor junctions

Transport property in diffusive normal metal/conventional superconductor (DN/CS) junctions is studied for the effect of spin fluctuations under various situations by solving the Usadel equation with Nazarov's generalized boundary condition. Tunneling conductance of the DN/CS junctions is calculated by changing the magnitude of the resistance in DN, Thouless energy in DN, and the transparency of the insulating barrier, together with the magnitude of spin fluctuations. A zero-bias conductance dip (ZBCD) and a zero-bias conductance peak (ZBCP) with the width given by Thouless energy occur in line shapes by way of a coherent Andreev reflection (CAR) around zero energy in the system of DN/CS junctions. We have found that both of the ZBCD and the ZBCP sharpen with increasing the magnitude of spin fluctuations in the region of the relatively large resistance in DN.