Pressure and angle-dependent shubnikov-de haas studies of the spin-density-wave state of α-(BEDT-TTF)2KHg(SCN)4

Shubnikov-de Haas (SdH) experiments involving pressures of up to 15 kbar, temperatures as low as 500 mK and magnetic fields as high as 17 T have been carried out in order to probe the proposed phase transition of α-(BEDT-TTF)2KHg(SCN)4 from a spin-density-wave (SDW) state at a pressure of Pc∼ 5 kbar. SdH measurements have also been carried out with the sample at a variety of field orientations. Frequencies of λ≈181 T, α≈671 T, μ≈775 T, ν≈856 T and β≈4270 T are observed in the Fourier spectra of the ambient pressure oscillations. The λ, μ, ν and β oscillations and also the large second harmonic component of the α orbit SdH waveform are not observed in the high field (>23T) metallic state, implying that they are a characteristics of the ambient pressure SDW state. Pressure suppresses the λ, μ and ν frequencies but the α and β orbits are seen at all pressures. The large second harmonic of the waveform of the α orbit SdH is initially suppressed by pressure but re-emerges above ∼10 kbar. The origins of this are discussed.