Nuclear spin-lattice relaxation in narrow gap semiconductors TiPtSn and ZrPtSn

The half-Heusler-type compounds TiPtSn and ZrPtSn have been studied by 195Pt nuclear magnetic resonance spectroscopy (NMR) at temperatures between 15 and 320 K. At low temperatures, the NMR spin-lattice relaxation rate in TiPtSn reveals Korringa behaviour, indicating a very low residual density of states at the Fermi level. High-temperature relaxation rate exhibits a semiconductor-like thermally activated behaviour. These results provide an experimental indication that the gap in TiPtSn is actually a pseudogap, with small density of carriers at the Fermi level.The temperature dependence of 195(1/T1) in ZrPtSn is distinctly different from that in TiPtSn and characteristic for extrinsic semiconductivity due to a presence of shallow impurities.