Cold Neutron Inelastic Scattering Measurements of the Spin-Peierls and Antiferromagnetic Excitations in Si-doped CuGeO₃ Single Crystals

抄録

Cold neutron inelastic scattering experiments on four CuGe_1-xSi_xO₃ single crystals with x=0, 0.004, 0.01, and 0.02 have been performed to study the effects of Si doping on the antiferromagnetic (AFM) and spin-Peierls (SP) excitations with high energy resolution. The intrinsic energy width Γ of the AFM excitation measured along the c ^* ([001]) direction near the magnetic zone center (0, 1, ½) (q=0) varies as q² for q le0.032 Å^{-1 = 0.06q_ZB}. This observation directly supports the recent theoretical predictions of Saito and Fukuyama. For pure CuGeO₃ the intrinsic SP excitation energy width appears to be resolution-limited up to 0.085 Å^-1. Upon doping, the widths of the SP excitations increase dramatically, but they are weakly q-dependent in the range we investigated. At x=0.02 the SP phase is lost. The existence of a second gap in CuGeO₃, first observed by A " in et al., is also confirmed. This second gap, which is quite sharp in the pure compound, is considerably broadened at Si concentrations as low as x=0.004.