Pressure effects on the low temperature states of the /spl alpha/-(BEDT-TTF)/sub 2/MHg(SCN)/sub 4/ organic conductor family

Summary form only given. We report the pressure dependence of the low temperature - high magnetic field properties of /spl alpha/-(BEDT-TTF)/sub 2/MHg(SCN)/sub 4/ (M =K, Rb, Tl, or NH/sub 4/). Both pressure clamp (to 10 kbar) and diamond anvil (to 25 kbar) devices have been employed. We find that the size of the closed orbits increases with pressure, that magnetic breakdown between open and closed orbit bands is pressure dependent, and that in some cases pressure induced nesting of the open orbits bands is observed. For the superconducting member M = NH/sub 4/ we find dTc/dP = - 4K/kbar, and the density wave states for M = Rb, Tl, and K are removed above 6 kbar.