Quantum Spin Excitations in the Spin-Peierls System CuGeO3

The complete spectrum of the double spinon excitation in the spin-Peierls system CuGe${\mathrm{O}}_3$ is mapped as a function of temperature for the first time. The spin dynamics of the lower boundary and the excitation continuum evolve quite differently. Moreover, the dimerization of the lattice produces a sharp excitation in the lower energy boundary at the edge of the Brillouin zone, as well as the well known spin-gap opening at the zone center.