Quantum phases of dipolar rotors on two-dimensional lattices

TL;DR

This paper investigates quantum phase transitions of dipolar rotors on 2D square and triangular lattices using quantum Monte Carlo, revealing various orientational phases influenced by interaction strength and electric field.

Contribution

It introduces a detailed phase diagram of quantum dipolar rotors on 2D lattices, highlighting novel orientational phases and transitions driven by anisotropic dipole interactions and external fields.

Findings

Disordered to polarized phase transition on triangular lattices.

Disordered to striped ordered phase on square lattices.

Identification of anisotropic long-range interaction effects.

Abstract

The quantum phase transitions of dipoles confined to the vertices of two dimensional (2D) lattices of square and triangular geometry is studied using path integral ground state quantum Monte Carlo (PIGS). We analyze the phase diagram as a function of the strength of both the dipolar interaction and a transverse electric field. The study reveals the existence of a class of orientational phases of quantum dipolar rotors whose properties are determined by the ratios between the strength anisotropic dipole-dipole interaction, the strength of the applied transverse field, and the rotational constant. For the triangular lattice, the generic orientationally disordered phase found at zero and weak values of both dipolar interaction strength and applied field, is found to show a transition to a phase characterized by net polarization in the lattice plane as the strength of the dipole-dipole interaction is increased, independent of the strength of the applied transverse field, in addition to the expected transition to a transverse polarized phase as the electric field strength increases. The square lattice is also found to exhibit a transition from a disordered phase to an ordered phase as the dipole-dipole interaction strength is increased, as well as the expected transition to a transverse polarized phase as the electric field strength increases. In contrast to the situation with a triangular lattice, on square lattices the ordered phase at high dipole-dipole interaction strength possesses a striped ordering. The properties of these quantum dipolar rotor phases are dominated by the anisotropy of the interaction and provide useful models for developing quantum phases beyond the well-known paradigms of spin Hamiltonian models, realizing in particular a novel physical realization of a quantum rotor-like Hamiltonian that possesses an anisotropic long range interaction.