Field-induced spin-density-wave phases in TMTSF organic conductors: Quantization versus nonquantization

Abstract

We study the magnetic-field-induced spin-density-wave (FISDW) phases in TMTSF organic conductors in the framework of the quantized nesting model. In agreement with recent suggestions, we find that the SDW wave vector Q deviates from its quantized value near the transition temperature T_c for all phases with quantum numbers N>0. Deviations from quantization are more pronounced at low pressure and higher N and may lead to a suppression of the first-order transitions N+1→ N for N>∼5. Below a critical pressure, we find that the N=0 phase invades the entire phase diagram in accordance with earlier experiments. We also show that at T=0, the quantization of Q and hence the Hall conductance is always exact. Our results suggest a novel phase transition/crossover at intermediate temperatures between phases with quantized and nonquantized Q.