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

We present an experimental investigation of the finite bias anomaly in the tunneling density of states of superconducting Al films above the paramagne tic limit. We show that the anomaly is a manifestation of a new fluctuation mechanism that forms a pseudogap near the Zeeman energy. The field depende nce of the anomaly energy is in good agreement with the recent theory of Al einer and Altshuler, provided that the proper normal-state Lande a factor i s used. We argue that the normal-state g factor is reduced from the bare va lue of g(n) = 2 to g(n) - 1.7 by a negative exchange field in the paramagne tic phase. [S0031-9007199)09200-5].