The standard model for the field-induced spin-density-wave (FISDW) transitions in the Bechgaard salts (TMTSF)2X, where TMTSF is tetramethyltetraselenafulvalene, explains a cascade of phase trasitions with each phase associated with the quantum Hall effect. The ClO4 salt is sufficiently different that it has inspired a series of theoretical modifications from the standard model. To test these models we have performed simultaneous xx, xy, specific-heat, magnetocaloric effect, and magnetization measurements in the field range from 09 T. We find that all of the transport transitions, specifically the Hall resistance jumps, are associated with thermodynamic transitions. We observe the emergence of a new FISDW state characterized by a distinct Hall plateau. It arises from what was originally believed to be a tetracritical point in the phase diagram. We find no evidence for an arborescent phase diagram, but rather the signature of a single pairwise splitting of the phase boundaries. The higher-field transitions are decidedly first order, hysteretic, and lossy. Anion disorder decreases the number of observed phases and shifts the transition fields.
ASJC Scopus subject areas
- Condensed Matter Physics