Sound Velocity Measurements near the Superconducting Transition Temperature of κ-(BEDT-TTF)2Cu[N(CN)2]Br under the Magnetic Field

Abstract

Layered organic superconductor κ‐(BEDT‐TTF)2Cu[N(CN)2]Br shows a step‐like softening in the sound velocity below the superconducting transition temperature. In this study, we have measured the sound velocity in the superconducting state of κ‐(BEDT‐TTF)2Cu[N(CN)2]Br in the applied magnetic field for various directions. The sound velocity as a function of the applied magnetic field shows remarkable elastic anomalies around H = 2 T. It was found that, the magnetic field parallel to the conducting planes of κ‐(BEDT‐TTF)2Cu[N(CN)2]Br, the sound velocity shows a sharp peak, which is considered to be related to the pinning by Josephson vortices.