Ground state with nonzero spontaneous magnetization of the two-dimensional spin-1/2 Heisenberg antiferromagnet with frustration

TL;DR

This study investigates the ground state properties of a frustrated two-dimensional spin-1/2 Heisenberg antiferromagnet on a pyramid lattice, revealing a potential new phase with nonzero spontaneous magnetization.

Contribution

It provides numerical evidence for a novel phase with small but finite spontaneous magnetization in a frustrated 2D antiferromagnet, near the square-lattice limit.

Findings

Identification of a new phase with nonzero spontaneous magnetization

Numerical evidence from finite-size diagonalization up to 39 sites

Observation of phase transition behavior near the square-lattice limit

Abstract

The S = 1/2 Heisenberg antiferromagnet on the two-dimensional pyramid lattice is studied by the numerical-diagonalization method. This lattice is obtained by the combination of the Lieb lattice and the square lattice. It is known that when interaction on the square lattice is increased from the ferrimagnetic limit of strong interaction on the Lieb lattice, this system shows gradual decrease and disappearance of spontaneous magnetization in the ground state. The present study treats the region near the case of the square-lattice antiferromagnet accompanied by isolated spins by numerical-diagonalization calculations of finite-size clusters with the maximum size of 39 sites. Our numerical results suggest the existence of a new phase with small but nonzero spontaneous magnetization between two zero-spontaneous-magnetization phases.