B-T-P phase diagram of alpha-(BEDT-TTF)(2)KHg(SCN)(4)

We present detailed studies of the B-T-P phase diagram of alpha-(BEDT-TTF)( 2)KHg(SCN)(4) by means of magnetic torque and magnetoresistance measurement s. The phase diagram for magnetic field oriented almost perpendicular to th e highly conducting layers closely resembles that expected for a charge-den sity-wave (CDW) system with an imperfectly nested Fermi surface. The influe nce of pressure can be readily understood as deteriorating the nesting cond itions and thus enhancing the role of the orbital effect of magnetic field. At field strongly tilted from the normal to the layers, both the torque an d magnetoresistance display a number of irreversible features that may be a ssociated with a series of first-order phase transitions. This behaviour is not understood within the existing CDW theories.