Magnetization plateau in a two-dimensional multiple-spin exchange model

TL;DR

This paper investigates a two-dimensional multiple-spin exchange model on a triangular lattice, revealing a magnetization plateau at half saturation due to four-spin interactions, with implications for low-density solid 3He films.

Contribution

It demonstrates the existence of a 1/2-magnetization plateau caused by four-spin exchange interactions and discusses its stability against fluctuations, linking it to experimental observations in 3He films.

Findings

A magnetization plateau at m/m_{sat}=1/2 was identified.

The plateau state is a collinear 'uuud' configuration.

The plateau persists despite quantum and thermal fluctuations.

Abstract

We study a multiple-spin exchange model on a triangular lattice, which is a possible model for low-density solid 3He films. Due to strong competitions between ferromagnetic three-spin exchange and antiferromagnetic four-spin one, the ground states are highly degenerate in the classical limit. At least 2^{L/2}-fold degeneracy exists on the L*L triangular lattice except for the SO(3) symmetry. In the magnetization process, we found a plateau at m/m_{sat}=1/2, in which the ground state is "uuud state" (a collinear state with four sublattices). The 1/2-plateau appears due to the strong four-spin exchange interaction. This plateau survives against both quantum and thermal fluctuations. Under a magnetic field which realizes the "uuud" ordered state, a phase transition occurs at a finite temperature. We predict that low-density solid 3He thin films may show the 1/2-plateau in the magnetization process. Experimental observation of the plateau will verify strength of the four-spin exchange. It is also discussed that this magnetization plateau can be understood as an insulating-conducting transition in a particle picture.