Structure of the mean-field yrast spectrum of a two-component Bose gas in a ring: role of interaction asymmetry

TL;DR

This paper explores how interaction asymmetry affects the structure and stability of the yrast spectrum in a two-component Bose gas on a ring, revealing complex state transitions and implications for persistent currents.

Contribution

It provides a detailed numerical analysis of how interaction asymmetry modifies the emergence and stability of plane-wave and soliton states in the yrast spectrum.

Findings

Interaction asymmetry alters the critical curves for plane-wave state emergence.

We identify continuous evolution and branch crossing mechanisms for state transitions.

Results impact understanding of persistent currents in asymmetric two-component Bose gases.

Abstract

The mean-field yrast spectrum of an SU(2)-symmetric two-component Bose gas confined to a ring geometry is known to exhibit an intricate nonanalytic structure that is absent in single-component systems. In particular, due to the interplay between the species concentration and the atomic interactions, a sequence of plane-wave states can emerge as yrast states at fractional values of the angular momentum per particle. This behavior stands in sharp contrast to the single-component case, where plane-wave states occur only at integer angular momenta. In this paper, we investigate how the structure of the yrast spectrum in a two-component Bose gas is modified by interaction asymmetry. By numerically solving the coupled Gross-Pitaevskii equations for propagating soliton states, we compute the mean-field yrast spectrum and, in particular, determine the critical curves associated with the emergence of various plane-wave yrast states. We find that both the behavior of these critical curves and the mechanisms by which plane-wave yrast states arise depend sensitively on the relative strengths of the inter- and intra-component interactions. When the intra-component interaction is weaker, the plane-wave yrast states replace soliton states through a continuous evolution, as in the SU(2)-symmetric case, although the conditions for their existence become more restrictive. In contrast, when the intra-component interaction is stronger, plane-wave yrast states may emerge by overtaking soliton states via branch crossings, and their stability is significantly enhanced. Our results have important implications for the existence and stability of persistent currents in asymmetric, two-component Bose gases.