Origin of the Field-Induced SDW in the Bechgaard Salts

Abstract

The energetic gain giving rise to the magnetic-field-induced SDW state in the Bechgaard salts is clarified to originate in the effect of the field to the electronic orbital motion. A variational total energy of the SDW state under the field is obtained on the basis of the anisotropic two-dimensional Hubbard model. Its semi-classical and fully quantum evaluations for the case of the most basic set of the SDW wave vector and the magnetization clearly show a gain of the total energy under the field, which is in fair agreement with the observed increase of the perpendicular magnetic susceptibility. The total energy proves to be lowered by quantization of the closed orbits, since the zero-field state density in the energy region of closed-orbits is a decreasing function of energy. The nature of the successive SDW phase transitions under the field is briefly discussed.