Magnetoresistive effects in the upper critical fields of heavy-fermion superconductors

The magnetoresistances of U6Fe, U6Co, and UPt3 have been measured and found to follow a novel, universal behavior at low temperatures. The data have been used to create the first quantitative model of the anomalous critical fields Hc2 of these compounds. An empirical analysis suggests that Hc2 and Tc are limited by a low-energy scale T0 that is comparable to the coherence temperature and related to the T2 coefficient of electrical resistivity. These results point to the existence of a novel pairing interaction that persists over a broad range of fermion-mass ratios 10m*me100.