Quantum Cascade of Field-Induced SDW Phases in Quasi-1D Conductors

Abstract

The metallic open Fermi surface of quasi-1D conductors, such as the (TMTSF)2X family, is destabilized in moderate magnetic fields inducing a semi-metallic SDW phase. The origin of this phenomenon is a quantum interference effect: Because of phase coherence between the SDW and the electron-hole wave function, the susceptibility diverges at low T for a set of quantized wavevector, leading to a metal SDW critical line made of a succession of segments, each of them labelled by a quantum number. Below this line, we expect, in increasing field, a cascade of first-order transitions between SDW phases corresponding to different quantum numbers, as observed recently in salts of the (TMTSF)2X family. Within each phase, SDW ordering and orbital quantization open an infinite series of gaps in the quasi-particle spectrum. The wave vector is quantized so that the Fermi level lies in the middle of a Landau gap. Significant departures from BCS behaviour are predicted.