The quadrupolar phases of the S=1 bilinear-biquadratic Heisenberg model on the triangular lattice

TL;DR

This paper maps out the phase diagram of the S=1 bilinear-biquadratic Heisenberg model on a triangular lattice, revealing complex quadrupolar phases, their excitations, and coexistence with magnetic order, with implications for real magnets.

Contribution

It provides a detailed phase diagram of the model using multiple theoretical methods, highlighting novel quadrupolar phases and their properties.

Findings

Ferroquadrupolar order can coexist with short-range helical magnetic order.

The antiferroquadrupolar phase exhibits a 2/3 magnetization plateau.

Implications for real S=1 magnetic materials are discussed.

Abstract

Using mean-field theory, exact diagonalizations and SU(3) flavour theory, we have precisely mapped out the phase diagram of the S=1 bilinear-biquadratic Heisenberg model on the triangular lattice in a magnetic field, with emphasis on the quadrupolar phases and their excitations. In particular, we show that ferroquadrupolar order can coexist with short-range helical magnetic order, and that the antiferroquadrupolar phase is characterized by a remarkable 2/3 magnetization plateau, in which one site per triangle retains quadrupolar order while the other two are polarized along the field. Implications for actual S=1 magnets are discussed.