Mysterious ground states in the organic conductor α-(BEDT-TTF)2KHg(SCN)4 : Mixed SDW and CDW?

We present magnetoresistance measurements in static fields up to 30T on the organic conductor α-(BEDT-TTF)2KHg(SCN)4. The current and field direction dependence of the magnetoresistance with respect to the crystallographic axis are described, suggesting a topological change of the Fermi surface. The change results from the phase transition from the normal metal to the mysterious ground state. We discuss a possible ground state of mixed charge-density and spin-density waves from the viewpoint of the orbital and Pauli couplings of the external field to the band electrons.