Exact magnetization plateaus and phase transitions in spin-S Heisenberg antiferromagnets in arbitrary dimensions

TL;DR

This paper extends the understanding of magnetization plateaus in Heisenberg antiferromagnets across arbitrary dimensions and spins, providing exact ground states, analyzing phase transitions, and confirming findings with numerical simulations.

Contribution

It generalizes exact ground state solutions for spin-S Heisenberg antiferromagnets in any dimension, revealing new phase transition mechanisms and validating results through numerical analysis.

Findings

Exact ground states for arbitrary spin in D dimensions.

Identification of first order phase transitions along magnetization plateaus.

Numerical phase diagram for a spin-1 chain matches analytical predictions.

Abstract

We generalize a class of Heisenberg antiferromagnets in one, two and three dimensions, which have been shown to exhibit magnetization plateaus for spin-1/2. In a certain parameter range of the general model, which is formally defined in D dimensions, we obtain the exact ground state(s) in the presence of an external magnetic field for arbitrary values of spin. In this range, the magnetization remains a constant as a function of the external field, except at some special values of the field where there is a jump from one plateau to the next. The plateaus are formed at certain specific fractions of the full magnetization which are determined by the spin and the lattice. Our general spin-S result reproduces the known cases for spin-1/2 in various lattices. Furthermore, we argue that outside the exact regime, the mechanism for the plateau formation is different. This results in first order phase transitions along some of the plateaus as the coupling constant is varied. We rigorously show the existence of such transitions for some particular cases. Finally, we numerically analyze a spin-1 model in one dimension using exact diagonalization to obtain its complete phase diagram. It agrees with our analytic results.