Theory of field-induced spin-density-wave in Bechgaard salts

Abstract

A variational formulation taking account of the magnetic field is presented for the spin-density-wave (SDW) ground state in an anisotropic two-dimensional Hubbaard model. The energy of the SDW state calculated in the fully quantum method is shown to be lowered in the field due to quantization of closed orbits formed in the k-space around the SDW gap. Minimization of this energy with respect to the SDW parameters leads to the finding that, when the weaker transfer energy t b is greater than a critical value t b, cr , many local minima exist corresponding to SDW subphases with different parameters. The phase diagram of the subphases with the lowest energy is constructed in the plane of the magnetic field versus t b . Anomalies in the thermodynamic and transport properties in the field-induced SDW state in Bechgaard salts are shown to be fairly well understable in terms of the successive first-order transitions among the SDW subphases in the changing field.