Incipient superconductivity and NFL behavior in off-stoichiometric Ce1+xNi2+yGe2+z polycrystals

The influence of composition on the physical properties of CeNi2Ge2 was stu died by measuring the resistivity of slightly off-stoichiometric Ce1+xNi2+y Ge2+z polycrystals at low temperatures (0.01 K less than or equal to T less than or equal to 6 K). We establish a clear correlation between compositio n, residual resistivity rho(o) and incipient superconductivity, i.e. a drop in rho(T). The lowest rho(o) values and the largest reductions in resistiv ity, reaching rho = 0 for one particular sample, were observed in slightly Ni-rich samples. A weak decrease of the unit-cell volume with increasing Ni -content suggests a slightly larger 4f-hybridization in those Ni-rich sampl es. The exponent epsilon of the (rho - rho(0)) similar to T-E behavior foun d for T less than or equal to 2 K correlates with the residual resistivity. While epsilon = 1.5 is observed for rho(0) greater than or equal to 3 mu O mega cm, 1.3 less than or equal to epsilon <1.5 was found for 0.17 mu Omega cm less than or equal to rho(0) < 3 mu Omega cm. (C) 2000 Elsevier Science B.V. All rights reserved.