Submillimeter Wave ESR Study of Spin Gap Excitations in CuGeO3

TL;DR

This study uses submillimeter wave ESR to investigate spin gap excitations in CuGeO3, revealing the breakdown of selection rules, the energy gap value, and effects of doping on excitation broadening.

Contribution

It provides the first ESR observation of singlet-triplet transitions in CuGeO3 and analyzes the influence of Dzyaloshinsky-Moriya interaction and doping effects.

Findings

Energy gap at zero field is 570 GHz (2.36 meV).

Strong field orientation dependence of absorption intensity.

Doping with 0.5% Si causes significant broadening of absorption lines.

Abstract

Transitions between the ground singlet state to the excited triplet state has been observed in CuGeO3 by means of submillimeter wave electron spin resonance. The strong absorption intensity shows the break down of the selection rule. 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 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.