Elementary excitations of ultracold soft-core bosons across the superfluid-supersolid phase transition

TL;DR

This study explores the excitation spectrum of 2D soft-core bosons across the superfluid to supersolid phase transition, revealing how phonon energies evolve and connect between phases using mean field and Quantum Monte Carlo methods.

Contribution

It demonstrates the applicability of Bogoliubov-de Gennes equations at high interaction strengths and links phonon energies across the phase transition.

Findings

Maximum phonon energy in supersolid connects to superfluid maxon energy.

Bogoliubov-de Gennes equations remain valid at high interaction strengths.

Phase transition characterized by changes in excitation spectrum.

Abstract

We investigate the zero-temperature excitation spectrum of two-dimensional soft-core bosons for a wide range parameters and across the phase transition from a superfluid to a supersolid state. Based on mean field calculations and recent Quantum Monte Carlo results, we demonstrate the applicability of the Bogoliubov-de Gennes equations, even at high interaction strengths where the system forms an insulating cluster crystal. Interestingly, our study reveals that the maximum energy of the longitudinal phonon band in the supersolid phase connects to the maxon energy of the superfluid at the phase transition.