PRESSURE AND ANGLE-DEPENDENT SHUBNIKOV-DE-HAAS STUDIES OF THE SPIN-DENSITY-WAVE STATE OF ALPHA-(BEDT-TTF)(2)KHG(SCN)(4)

Shubnikov-de Haas (SdH) experiments involving pressures of up to 15 kb ar, 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 alpha-(BEDT-TTF)(2)KHg(SCN)(4) from a spin-density-wave (SDW) state at a pressure of P-c similar to 5 kbar. SdH measurements have also be en carried out with the sample at a variety of field orientations. Fre quencies of lambda approximate to 181 T, alpha approximate to 671 T, m u approximate to 775 T, nu approximate to 856 T and beta approximate t o 4270 T are observed in the Fourier spectra of the ambient pressure o scillations. The lambda, mu, nu and beta oscillations and also the lar ge second harmonic component of the alpha orbit SdH waveform are not o bserved in the high field (>23T) metallic state, implying that they ar e a characteristic of the ambient pressure SDW state. Pressure suppres ses the lambda, mu and nu frequencies but the a and P orbits are seen at all pressures. The large second harmonic of the waveform of the a o rbit SdH is initially suppressed by pressure but reemerges above simil ar to 10 kbar. The origins of this are discussed.