Submillimeter Wave ESR Study of Spin Gap Excitations in CuGeO3

Abstract

Transitions between the ground singlet state and the excited triplet state have been observed in CuGeO3 by means of submillimeter wave electron spin resonance. The energy gap at zero field is evaluated to be 570 GHz (2.36 meV) and this value is nearly identical to the gap at the zone center observed by inelastic neutron scattering. The absorption intensity shows strong field orientation dependence, but it shows no significant dependence on magnetic field intensity. These features have been explained by considering the existence of Dzyaloshinsky-Moriya (DM) antisymmetric exchange interaction. The doping effect on this singlet-triplet excitation has been also studied. A drastic broadening of the absorption line is observed by the doping of only 0.5 % of Si.