U2Co2Sn: An undoped non-Fermi-Iiquid system with C-e approximate to gamma-A root T

Investigation of the low-temperature specific heat, magnetic susceptibility , and resistivity of U2Co2Sn for expected paramagnon behavior led instead t o the discovery of a non-Fermi-liquid system obeying the Millis/Moriya theo ry prediction of an electronic specific beat that varies approximately as g amma-A root T over an appreciable temperature range, in this case over the whole temperature range (0.3-10 K) of measurement. The temperature dependen ce of the low-temperature resistivity, however, follows rho = rho(0) + A T- alpha, with alpha(approximate to 1.8) lying below that predicted for a Ferm i liquid (i.e., alpha = 2) but above the rho = rho(0) + A T-1.5 predicted b y the quantum phase transition, weakly interacting spin fluctuation theory of millis/Moriya. Scaling of the specific heat with field indicates that th e electron interactions responsible for the non-Fermi-liquid behavior are n ot single ion in nature. Several non-Fermi-liquid theories and their possib le applicability to these results are discussed, as well as the possible in fluence of the relatively small U-U spacing in U2Co2Sn on the unusual non-F ermi-liquid behavior.