Theory of Successive Field-Induced First Order Transitions in Quasi-Two Dimensional Conductors

Abstract

We have investigated the first order field induced phase transitions observed in α-(BEDT-TTF)₂MHg(SCN)₄ (M=K, Rb and Tl) 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.