Electron-Spin-Resonance Study of the High-Field Phase of the Spin-Peierls System Tetrathiafulvalene-Au-bis-dithiolene

We present ESR data obtained in the high-field phase of the spin-Peierls system tetrathiafulvalene-Au${\mathrm{S}}_4$ ${\mathrm{C}}_4$ ${\left(\mathrm{C}{\mathrm{F}}_3\right)}_4$ (TTF-AuBDT). The measurements were performed on single crystals, and are the first ESR measurements performed in the high-field phase of this system. Our results demonstrate for the first time a marked effect of the magnetic structure of the high-field phase of a spin-Peierls system on the ESR spectrum. The data are analyzed in terms of the available theories for spin-Peierls systems. The results are in good agreement with the predictions of the theory.