Inter-grain coupling of granular MgB2 superconductor in an applied AC magnetic field

Abstract

We investigate inter-grain coupling in granular MgB₂ via AC magnetic susceptibility χ(T) measurements and simulations. We deduced the inter­-grain resistance R(T) which determines the behavior of χ(T). We show that R(T) is dependent on inter-grain tunneling conductance G(T) that characterizes quasi-particle tunneling, and the critical current i(T) of the Josephson tunnel junction in between grains. Our simulations utilizes the phenomenological model for AC loss generation in granular supercon­ductors for low magnetic fields and the deduced inter-grain resistance R(T) components of the χ(T). Our results suggest that as the applied field amplitude is increased, Josephson tunneling is suppressed which allows for more quasi-particle tunneling. The self-inductance is also de­creased which indicates that there is less number of grains that can cou­ple with increased magnetic field amplitude.