Cu Nuclear Quadrupole Resonance Study of CuGeO₃

Abstract

We have observed the nuclear quadrupole resonance (NQR) of Cu in the spin-Peierls system CuGeO₃. The NQR signals have been observed at 34.23± 0.02, MHz for ⁶³Cu and 31.66± 0.02, MHz for ⁶⁵Cu at 4.2, K under zero external field. These signals persist down to 1.3, K with neither line splitting nor broadening due to the internal magnetic field. This fact indicates there is no long-range order of Cu spins. The ⁶³Cu nuclear spin-lattice relaxation rate ⁶³(1/T₁) rapidly drops below 15, K which clearly demonstrates an opening of the energy gap in the excitation spectrum. However, no anomaly was detected in the Cu NQR frequency at the transition temperature. It was also found that ⁶³(1/T₁) above 15, K smoothly extrapolates to a finite value at 0, K. This may suggest the spin dynamics in the paramagnetic state is described in terms of the one-dimensional antiferromagnetic Heisenberg model with S=1/2.