Exchange fields and the finite bias tunneling anomaly in paramagnetically limited superconducting Al films

V. Yu Butko, Louisiana State University
P. W. Adams, Louisiana State University
I. L. Aleiner, Stony Brook University


We present an experimental investigation of the finite bias anomaly in the tunneling density of states of superconducting Al films above the paramagnetic limit. We show that the anomaly is a manifestation of a new fluctuation mechanism that forms a pseudogap near the Zeeman energy. The field dependence of the anomaly energy is in good agreement with the recent theory of Aleiner and Altshuler, provided that the proper normal-state Landé g factor is used. We argue that the normal-state g factor is reduced from the bare value of gn = 2 to gn ˜ 1.7 by a negative exchange field in the paramagnetic phase. © 1999 The American Physical Society.