Density and pseudo-spin rotons in a bilayer of soft-core bosons

TL;DR

This paper investigates the collective excitations and instabilities in a bilayer of soft-core bosons with Rydberg-dressed interactions, revealing roton minima and phase transitions driven by density and layer asymmetry.

Contribution

It introduces a mean-field analysis of density and pseudo-spin rotons in bilayer soft-core bosons, highlighting how layer density and symmetry breaking influence instabilities.

Findings

Roton minima appear in symmetric and asymmetric density modes.

Homogeneous superfluid becomes unstable to density or pseudo-spin-density waves.

Layer asymmetry and counterflow enhance susceptibility to density-wave instabilities.

Abstract

We study the dynamics of a bilayer system of bosons with repulsive soft-core Rydberg-dressed interactions within the mean-field Bogoliubov-de Gennes approximation. We find roton minima in both symmetric and asymmetric collective density modes of the symmetric bilayer. Depending on the density of bosons in each layer and the spacing between two layers, the homogeneous superfluid phase becomes unstable in either (or both) of these two channels, leading to density and pseudo-spin-density wave instabilities in the system. Breaking the symmetry between two layers, either with a finite counterflow or a density imbalance renormalizes the dispersion of collective modes and makes the system more susceptible to density-wave instability.