Tunable magnetic phases in quasi-one-dimensional systems

TL;DR

This paper explains the emergence of various magnetic phases and spin phenomena in quasi-one-dimensional systems using a 3D Coulomb interaction model, revealing how confinement and magnetic fields influence spin polarization and conductance features.

Contribution

It introduces a comprehensive Hartree-Fock model that accounts for complex magnetic phase patterns in quasi-1D systems, explaining experimental observations without spin-orbit interactions.

Findings

Degenerate excited state with opposite spin polarization above a threshold

Spin polarization varies with confinement and magnetic field

Conductance plateau at half the quantum conductance observed

Abstract

There has been considerable debate on the onset of exotic spin phenomena in quantum wires due to enhanced many-body effects caused by the one-dimensional (1D) alignment of charge carriers. We explain various observed spin effects, such as a carrier density-dependent spin-flip in dilute quasi-1D systems and the variability of the spin polarization in quantum point contacts, by using an unrestricted Hartree-Fock approach with a three-dimensional (3D) Coulomb interaction. The model dimensionality is critical in identifying a complex pattern of magnetic phases varying with confinement and magnetic field. In the limit of vanishing magnetic fields, we show the emergence of a degenerate excited state with opposite spin polarization above a confinement-dependent 1D concentration threshold, which is consistent with observations of a conductance plateau at half the conductance quantum $G_{0}/2=e^{2}/h$, even in the absence of spin-orbit interactions. Moreover, spin polarization disappears in highly-asymmetrically confined wires, and strictly two-dimensional systems.