Magnetoresistance of CeCu2Si2: Differences and similarities to UBe13

The magnetoresistance of nonsuperconducting CeCu1.9Si2 and superconducting CeCu2.2Si2 was measured for temperatures between 1.4 and 25 K and magnetic fields to 14 T. For temperatures larger than 5 K, both sets of data satisfy a scaling relation derived for the conventional single-channel Kondo model. According to the magnetoresistance, the single ion characteristic temperature T-0 for CeCu1.9Si2 is about 30% smaller than that for CeCu2.2Si2. The T-0 values are in good agreement with the ones obtained from the low-temperature magnetic susceptibility but are larger than the characteristic temperatures derived from the low-temperature specific heat. This disagreement is especially large for the superconducting sample (by a factor of 2). The magnetoresistance results point to a fundamental difference between the low-temperature states in CeCu2Si2 and UBe13 and possibly between other Ce- and U-based heavy fermions.