Anomalous suppression of T-c and moderate heavy fermion behaviour in YbNi2B2C

We have synthesized single phase material YbNi2B2C. Results of our X-ray diffraction and L(III)-edge studies are consistent with (nearly) trivalent state of Yb-ions in this material. Superconductivity is not observed down to 2 K in our resistivity and magnetic susceptibility studies. This is anomalous as, with Yb-ions in 3+ state, one expects T-C similar to 12K in this material on the basis of the systematic of T-C in other magnetic superconductors belonging to the series RNi(2)B(2)C (R, a rare earth ion). Resistivity is relatively temperature independent in the temperature range 50K-300K. However, below 50K there is a large reduction of resistivity. The Sommerfeld coefficient, gamma, obtained from the heat capacity data in the temperature range 12K-25K, is similar to 200 mJ/mol.K-2 which suggests the formation of a moderately heavy fermion state in YbNi2B2C at low temperatures. Suppression of superconductivity constitutes an independent evidence of anomalous state of Yb-ions in YbNi2B2C Copyright (C) 1996 Published by Elsevier Science Ltd