Acoustic de Haas-van Alphen Effect in Organic Superconductor α-(BEDT-TTF)₂NH₄Hg(SCN)₄

Abstract

Longitudinal sound velocity measurements propagating along the interlayer direction have been performed at 53.4 MHz by a phase comparison method on a quasi-two-dimensional (Q2D) organic superconductor α-(BEDT-TTF)₂NH₄Hg(SCN)₄ with T_c = 1 K. Temperature dependence of the sound velocity shows anomalies around 20 K and 60 K. The acoustic de Haas-van Alphen (dHvA) effects are observed below 1.8 K for the first time in these organic metals. The quantum oscillations originate from the α-Fermi surface (FS) of a weakly warped cylindrical shape. According to the theoretical formulations by Kataoka and Goto for an acoustic dHvA effect, the absolute area coefficient | Λ _L | is estimated to be about 3.5. The multiband term Λ_L^m is concluded to dominantly contribute to | Λ_L |.