V. H. Tran

U2Ru2Sn: a new Kondo insulator?

We present magnetic susceptibility, specific heat, electrical resistivity, magnetoresistance, Hall coefficient, thermal conductivity, thermoelectric power, and 119 Sn NMR data for U2Ru2Sn: Clear evidence is found for the formation of a gap in the electronic density of states at the Fermi level. Together with the disappearance of the local magnetic moments at low temperatures and the observation of enhanced effective masses this suggests to classify U2Ru2Sn as a Kondo insulator. r 2002 Elsevier Science B.V. All rights reserved.

Gap formation in the semimetal U2Ru2Sn: evidence from 119Sn NMR investigations

Abstract We report measurements of the 119 Sn nuclear spin-lattice relaxation rate 1/T1 and the Knight shift K for polycrystalline U2Ru2Sn powder samples as a function of temperature. The T dependence of 1/T1 is very similar to that of CeNiSn with the only difference that the temperature scale is increased roughly by a factor of 10. Therefore a first estimate gives a (pseudo-) gap value of Δ/k B ≈140 K ( ≈14 K for CeNiSn). At low temperatures similar to CeNiSn a T1T=constant behaviour is observed which indicates the presence of a residual density of states at the Fermi level N(EF) in the pseudo-gap. Knight shift measurements on oriented polycrystalline powder samples show nearly no magnetic anisotropy, whereas the temperature dependence roughly follows the behaviour of the magnetic susceptibility. First investigations on the non-magnetic reference compound Th2Ru2Sn are also discussed.

First results on U2Ru2Sn single crystals

The tetragonal compound U2Ru2Sn shares several properties with the strongly correlated semimetal CeNiSn. Here we present, for the first time, measurements of magnetic, thermal, and electrical transport properties of single-crystalline samples and compare them to results on polycrystals. The specific heat and the magnetic susceptibility provide evidence for the opening of an energy gap of approximately 150–160 K: Both the magnetic susceptibility and the electrical resistivity are anisotropic. The c-axis is the easy magnetic axis along which the resistivity is ‘metal-like’. The resistivity along the a-axis is ‘semiconductor-like’. r 2003 Elsevier Science B.V. All rights reserved.