SPIN-PEIERLS GAP AND 2-MAGNETIC-EXCITATION BOUND AND RESONANT STATES IN CU1-XZNXGEO3 AND CUGE1-YSIYO3

We study a spin-Peierls gap and a bound and a resonant states of two m agnetic excitations in Cu1-xZnxGeO3 and CuGe1-ySiyO3. Breakdown of the selection rule in the doped samples enables us to observe the spin-Pe ierls gap excitation in the first-order Raman process. It is found tha t this excitation shifts to lower frequency and merges into the tail o f the elastic scattering together with its line broadening with increa sing dopant concentration. The bound state of a particle-hole pair is observed just below the bottom of the second-order Raman band in pure CuGeO3. It changes into a resonant state and disappears rapidly as the concentration of the dopant is increased, owing to the weakening of a ttractive interaction and the extreme increase of the dampings of the magnetic excitations. These features are demonstrated theoretically by using Green's function.