High-field magnetotransport and Fermi-surface topology in the novel quasi-two-dimensional organic conductor bis(ethylenedithiolo)tetrathiafulvalenium mercuric postassium thiocyanate, (BEDT-TTF)2KHg(SCN)4

Abstract

Magnetotransport measurements have been carried out in the novel organic conductor (BEDT-TTF${)}_2$KHg(SCN${)}_4$. Some remarkable and unusual features were found in the high-field magnetoresistance measured under pulsed magnetic fields up to 40 T; a negative slope above 10 T, a sharp kink structure at 22.5 T, and large enhancement of the Shubnikov–de Haas oscillations above the kink structure. Angle-dependent quantum oscillations were also observed under static fields up to 12 T. The experimental results suggest strong two-dimensionality and presence of a weakly warped cylindrical Fermi surface whose cross section is anisotropic and 16% of that of the first Brillouin zone. Vanishing of an overlap between neighboring Landau subbands is proposed as one of possible origins of the sharp kink structure.