Phases and collective modes of bosons in a triangular lattice at finite temperature: A cluster mean field study

TL;DR

This study explores the finite temperature phases and collective excitations of bosons in a triangular lattice, revealing the presence of superfluid, density wave, and supersolid phases, with implications for cold atom experiments.

Contribution

It introduces a combined mean field and cluster mean field approach to analyze phase diagrams and collective modes in frustrated bosonic systems on a triangular lattice.

Findings

Identification of various phases including supersolids at finite temperature

Derivation of transition temperatures using Landau theory

Analysis of Goldstone and Higgs modes in supersolids

Abstract

Motivated by the realization of Bose-Einstein condensates (BEC) in non-cubic lattices, in this work we study the phases and collective excitation of bosons with nearest neighbor interaction in a triangular lattice at finite temperature, using mean field (MF) and cluster mean field (CMF) theory. We compute the finite temperature phase diagram both for hardcore and softcore bosons, as well analyze the effect of correlation arising due to lattice frustration and interaction systematically using CMF method. A semi-analytic estimate of the transition temperatures between different phases are derived within the framework of MF Landau theory, particularly for hardcore bosons. Apart from the usual phases such as density waves (DW) and superfluid (SF), we also characterize different supersolids (SS). These phases and their transitions at finite temperature are identified from the collective modes. The low lying excitations, particularly Goldstone and Higgs modes of the supersolid can be detected in the ongoing cold atom experiments.