Tunneling Resistances Associated with Classical-to-Quantum Fluctuations in Single Point-Contact Junction

Abstract

The studied single point-contact junction, which bridges superconducting (Pb) and ferromagnetic (Co) granular thin films, presents magnetic-field-insensitive nonlinear resistances versus biases at low temperature. This work shows that the disordered granules can cause random charge localizations δq as well as the resulting offset-bias δV=δq/Cj across the junction capacitance Cj, and thereby invalidate the (magnetic-field-dependent) energy-level structures of materials Pb and Co. Simultaneously, the disorder brings in the fundamental influences of the non-equilibrium fluctuations. A simple model by golden approximation is then addressed to demonstrate the basic fluctuation behaviors. The results indicates that quantum and thermal fluctuations mainly drive the behaviors of the differential resistances of this disordered system as the experimental observations.