Thermal transport properties of U2Ru2Sn at low temperatures

U2Ru2Sn has been classified as the first tetragonal U-based Kondo insulator. Here, we present measurements of the thermal conductivity kappa and thermopower S of high-quality single-crystalline U2Ru2Sn along and perpendicular to the tetragonal e-axis, in the temperature range between 100mK and 1 K, in zero field and in a magnetic field of 6T. Below 400mK, the phonon contribution to K(T) shows a T 2 behaviour for both directions that can be attributed to phonons scattered by electrons. S(T) presents a linear behaviour in the whole temperature range. S is positive along the c-axis and negative perpendicular to the c-axis. Using a one-band model the effective mass m* is estimated to be 2m(0) along and 16m(0) perpendicular to the c-axis, where m(0) is the free-electron mass. This indicates that U2Ru2Sn has a highly anisotropic residual density of states within the pseudogap. (c) 2005 Elsevier B.V. All rights reserved.