Magneto-Roton Modes of the Ultra Quantum Crystal: Numerical Study

TL;DR

This paper numerically investigates the Magneto-Roton modes in the ultra quantum crystal phases of Bechgaard salts, revealing a quasi-periodic structure of collective excitations and their evolution with magnetic field.

Contribution

It provides the first numerical estimates of Magneto-Roton mode energies and their anisotropy in these quantum phases, including the sign-reversed Ribault phase.

Findings

Confirmation of Magneto-Roton mode existence in the spectrum.

Numerical estimates of mode energies and anisotropy.

Distinct evolution of modes at low and high magnetic fields.

Abstract

The Field Induced Spin Density Wave phases observed in quasi-one-dimensional conductors of the Bechgaard salts family under magnetic field exhibit both Spin Density Wave order and a Quantized Hall Effect, which may exhibit sign reversals. The original nature of the condensed phases is evidenced by the collective mode spectrum. Besides the Goldstone modes, a quasi periodic structure of Magneto-Roton modes, predicted to exist for a monotonic sequence of Hall Quantum numbers, is confirmed, and a second mode is shown to exist within the single particle gap. We present numerical estimates of the Magneto-Roton mode energies in a generic case of the monotonic sequence. The mass anisotropy of the collective mode is calculated. We show how differently the MR spectrum evolves with magnetic field at low and high fields. The collective mode spectrum should have specific features, in the sign reversed "Ribault Phase", as compared to modes of the majority sign phases. We investigate numerically the collective mode in the Ribault Phase.