High-field electron spin resonance of Cu1-xZnxGeO3

High-field electron spin resonance measurements were made on powder samples of Cu1-xZnxGeO3 (x = 0.00, 0.01, 0.92, 0.03, and 0.05) at different frequencies (95, 110, 190, 220, 330, and 440 GHz) at low temperatures. The spectra of the doped samples show resonances whose positions are dependent on Zn concentration, frequency, and temperature. The analysis of the intensity variation of these lines with temperature allows us to identify them as originating from transitions within states situated inside the spin Peierls gap. A qualitative explanation of the details of the spectra is possible if we assume that these states in the gap are associated with "loose" spins created near the Zn impurities, as recently theoretically predicted. [S0031-9007(98)05429-5].