THEORY OF SUCCESSIVE FIELD-INDUCED FIRST-ORDER TRANSITIONS IN QUASI-2-DIMENSIONAL CONDUCTORS

We have investigated the first order field induced phase transitions observed in alpha-(BEDT-TTF)(2) MHg(SCN)(4) (M = K, Rb and TI) by examining theoretically the energetics of the magnetic breakdown phenomena in high fields (H) which were understood as a probabilistic process. Since the diamagnetic energy loss associated with the cyclotron motion is effectively lowered by taking a larger orbit in reciprocal space as H increases, the spin density wave (SDW) gap formed on an orbit can be eliminated by the ''break-through'' electrons. An origin of the field-induced reentrant transition from SDW to the normal state in those quasi-two dimensional conductors is attributed to this energetics. The quantum magnetic oscillation is predicted to yield a novel type of successive phase transitions where two phases are interwoven in a fine scale against H.