Sharp Magnetoabsorption Resonances in the Vortex State ofBi2Sr2CaCu2O8+δ

Abstract

We report the observation of narrow resonances in the absorption of mm wavelength radiation (30 to 50 GHz) in the vortex state of ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}\mathrm{Ca}{\mathrm{Cu}}_{2}{\mathrm{O}}_{8+\ensuremath{\delta}}$. When the applied field $\mathbf{B}(\ensuremath{\parallel}\mathbf{c})$ is swept at fixed frequency $\ensuremath{\omega}$, the absorption displays two distinct Lorentzian peaks at the resonance fields ${B}_{0}$ and ${B}_{1}$. The resonance frequency decreases with increasing field, consistent with anticyclotronic behavior. At fixed $\ensuremath{\omega}$, ${B}_{0}$ and ${B}_{1}$ also vary strongly with temperature $T$. ${B}_{0}$ and ${B}_{1}$ increase to a sharp maximum when $T$ crosses the vortex solid-to-liquid transition line inferred from resistivity results. The coupling of cyclotron resonance with collective modes giving rise to an anticyclotronic mode is discussed.