CU-63,CU-65 NMR AND NQR STUDY OF THE CU2-STATE AND THE SPIN DYNAMICS IN THE SPIN-PEIERLS COMPOUND CUGEO3( ELECTRONIC)

Cu-63,Cu-65 NMR and NQR measurements have been performed to study the Cu2+ electronic state and the spin dynamics in CuGeO3, which is an ino rganic compound that undergoes the spin-Peierls transition at T-sp sim ilar to 14 K. The NQR frequency is discussed in connection with the la ttice dimerization accompanied by the spin-Peierls transition. The Kni ght shift with an axial symmetry showed the temperature dependence cor responding to the reduction of the spin susceptibility. From the analy sis of the Knight shift and the magnetic susceptibility, orbital and s pin susceptibilities are evaluated. The analysis of the hyperfine stru cture leads to a conclusion that the electronic state of the Cu2+ ion above T-sp is described by a single-ion model in a crystal field with a tetragonal symmetry. The supertransferred hyperfine interaction, whi ch is one of the characteristic features of Cu2+ ions in the CuO2 plan e in the high-T-c superconducting copper oxides, is found not to play an important role in CuGeO3. The temperature dependence of the nuclear spin-lattice relaxation rate 1/T-1 clearly shows presence of a gap in the magnetic excitation spectrum below T-sp. The relaxation mechanism is discussed based on the spinless fermion treatment for an S = 1/2 o ne-dimensional Heisenberg antiferromagnet (1DHAF) above T-sp and for a nonuniform S = 1/2 1DHAF with two unequal and alternating exchange in teractions below T-sp. Above T-sp, it is also discussed in terms of th e dynamical susceptibility of the 1DHAF.