Crystalline Electric Field Manifestations in Tunneling into Superconductors

Abstract

The theory of Holzer et al.¹ predicts that the crystalline electric field should influence tunneling into superconductors containing rare earth impurities due to scattering between the crystal field split energy levels of the rare earth impurity. Their theory predicts that structure, in the form of conductance dips, should be observable in the tunneling conductance of junctions involving a superconductor with a rare earth impurity, and that the strongest structure should occur at V = Δ − δ mV, where Δ is the energy gap value and δ is the energy difference between the ground state and the first excited energy level of the rare earth impurity. They predict that the structure should be sharpest for singlet ground states and in all cases the overall tunneling conductance should be very BCS-like. In this paper, we will discuss the tunneling results of Lim and Leslie² on Bi-Pr, where structure in general agreement with the theory of Holzer et al. was observed, and compare them to the tunneling results of Nickel et al.³ on La-Pr, where no voltage dependent structure was observed.

Now at the Department of Electrical Engineering, University of Alberta, Edmonton, Alberta, Canada.