⁷⁵As NQR/NMR Study of Successive Phase Transitions and Energy Gap Formation in Kondo Semiconductor CeRhAs

Abstract

⁷⁵As NQR/NMR studies were performed to investigate the successive phase transitions found recently, the gap formation and their interplay in a Kondo semiconductor CeRhAs. NQR/NMR spectra in their respective phases change, reflecting lattice modulation modes, q₁=(0,\\frac12,\\frac12), q₂=(0,\\frac13,\\frac13) and q₃=(\\frac13,0,0). In particular for well-resolved three NQR lines corresponding to the q₃ mode in the lowest temperature phase, the nuclear spin–lattice relaxation rate (T₁T)⁻¹ shows an activation type T-dependence, suggesting a gap opening over the entire Fermi surface, in contrast to the V-shaped gap in isostructural CeNiSn and CeRhSb. The evaluated gap of 272 K and the bandwidth of about 4000 K are one order of magnitude larger than those in CeNiSn and CeRhSb. A lattice modulation forms a gap different from the V-shaped gap.