Angular dependence of the cyclotron effective mass in organic superconductors

Abstract

We report measurements of the de Haas–van Alphen (dHvA) effect in the organic superconductors α-(BEDT-TTF${)}_2$(${\mathrm{NH}}_4$)Hg(SCN${)}_4$ (${\mathit{T}}_{\mathit{c}}$≊1 K) and κ-(BEDT-TTF${)}_2$Cu(NCS${)}_2$ (${\mathit{T}}_{\mathit{c}}$≊10 K) in fields up to 15 T and temperatures down to 0.45 K. For the first time, we determine the angular dependence of the cyclotron effective mass ${\mathit{m}}_{\mathit{c}}$, and the orientation of up to four spin-splitting zeros of the dHvA signal. The angular dependence of the amplitude of the dHvA oscillations is quantitatively explained, and the mass enhancement due to electron-phonon coupling is estimated.