Projective studies of spin nematics in a quantum frustrated ferromagnet

TL;DR

This paper investigates the ground state of a frustrated quantum spin model using variational wavefunctions, revealing a nematic spin liquid state with specific symmetry-breaking properties.

Contribution

It introduces the projected Z2 planar state as a novel variational wavefunction that captures the nematic spin liquid phase in a frustrated ferromagnetic model.

Findings

Projected Z2 planar state has the lowest energy among competing states.

State exhibits quadrupole order breaking spin rotational symmetry.

Strong collinear antiferromagnetic fluctuations are observed.

Abstract

We study the ground state properties of the spin-1/2 frustrated ferromagnetic J1-J2 Heisenberg model on the square lattice, employing projected BCS wavefunctions with spin-triplet pairings of the spinon fields as trial wavefunctions. Based on the variational Monte Carlo analysis, we argue that, in the competing coupling regime, a certain type of the projected BCS wavefunction, dubbed the projected Z2 planar state, achieves the best optimal energy among the other competing states such as the ferromagnetic state and collinear antiferromagnetic state. Like in quantum spin liquids, the projected Z2 planar state preserves the translational symmetry of the square lattice. However, it is also accompanied by a d-wave ordering of the quadrupole moments, breaking the spin rotational symmetry. The state thus describes a quantum spin analogue of the nematic liquid crystals. The calculated static correlation functions also reveal that the projected Z2 planar state has a strong collinear antiferromagnetic fluctuation.