U2Co2Sn:An undoped non-Fermi-liquid system withCe≈γ−AT

Abstract

Investigation of the low-temperature specific heat, magnetic susceptibility, and resistivity of ${\mathrm{U}}_{2}{\mathrm{Co}}_{2}\mathrm{Sn}$ for expected paramagnon behavior led instead to the discovery of a non-Fermi-liquid system obeying the Millis/Moriya theory prediction of an electronic specific heat that varies approximately as $\ensuremath{\gamma}\ensuremath{-}A\sqrt{T}$ over an appreciable temperature range, in this case over the whole temperature range (0.3--10 K) of measurement. The temperature dependence of the low-temperature resistivity, however, follows $\ensuremath{\rho}={\ensuremath{\rho}}_{0}{+AT}^{\ensuremath{\alpha}},$ with $\ensuremath{\alpha}(\ensuremath{\approx}1.8)$ lying below that predicted for a Fermi liquid (i.e., $\ensuremath{\alpha}=2)$ but above the $\ensuremath{\rho}={\ensuremath{\rho}}_{0}{+AT}^{1.5}$ predicted by the quantum phase transition, weakly interacting spin fluctuation theory of Millis/Moriya. Scaling of the specific heat with field indicates that the electron interactions responsible for the non-Fermi-liquid behavior are not single ion in nature. Several non-Fermi-liquid theories and their possible applicability to these results are discussed, as well as the possible influence of the relatively small U-U spacing in ${\mathrm{U}}_{2}{\mathrm{Co}}_{2}\mathrm{Sn}$ on the unusual non-Fermi-liquid behavior.