Spin and density excitations of one-dimensional self-bound Bose-Bose droplets

TL;DR

This paper investigates the density and spin excitations in one-dimensional self-bound Bose-Bose droplets using Bogoliubov theory, revealing the emergence and observability of spin modes within the mean-field stability regime, supported by variational and real-time analyses.

Contribution

It provides a detailed analysis of spin and density excitations in 1D Bose-Bose droplets, highlighting the conditions for spin mode emergence and their experimental relevance, extending Petrov's original theory.

Findings

Spin excitations become prominent as interspecies coupling weakens.

Spin modes fall below particle-emission threshold at higher coupling, making them observable.

Theoretical results are supported by variational and real-time dynamic analyses.

Abstract

We study density and spin excitations of one-dimensional self-bound Bose-Bose droplets within Bogoliubov theory, and show that spin excitations come alive, especially as the interspecies coupling is made less attractive. We argue that spin excitations are particularly relevant in the one-dimensional droplet regime, where droplets are realized within the mean-field stability regime, as has been confirmed by the Quantum Monte Carlo simulations. As the interspecies coupling strength increases within the mean-field stability regime, spin modes ultimately fall below the particle-emission threshold, thus becoming observable in the droplet spectrum. We analyze the Bogoliubov model for both pseudospinor and population-imbalanced scalar mixtures, encompassing both the density and spin sectors, and corroborate our findings through variational analysis of density and spin breathing modes, as well as real-time dynamics. Additionally, we compare our results with Petrov's "original" theory, which considers the Lee-Huang-Yang (LHY) correction at the attractive edge of the mean-field stability regime and a beyond-LHY description of Bose-Bose mixtures.