Bifurcations, stability, and mode evolution in segregated condensate mixtures

TL;DR

This paper investigates the low energy excitations and mode evolution in two-component Bose-Einstein condensates, revealing bifurcations, zero energy modes, and Goldstone modes as functions of interaction strength in quasi-2D systems.

Contribution

It provides new insights into the excitation spectrum and mode bifurcations in segregated condensate mixtures using Hartree-Fock-Bogoliubov theory.

Findings

Observation of a new zero energy mode in $^{85}$Rb-$^{87}$Rb TBEC.

Bifurcation of the Kohn mode at the miscible-immiscible transition in $^{133}$Cs-$^{87}$Rb.

Softening of the lower energy mode leading to a new Goldstone mode.

Abstract

We present new features of low energy Bogoliubov quasiparticle excitations of a two component Bose-Einstein condensate (TBEC) in quasi-2D geometry at zero temperature using Hartree-Fock-Bogoliubov (HFB). We, in particular, consider the TBECs of $^{133}$Cs~-$^{87}$Rb and $^{85}$Rb~-$^{87}$Rb, and show specific features in the low energy excitation spectrum as a function of the interaction strength. For $^{85}$Rb~-$^{87}$Rb TBEC, the appearance of a new zero energy mode is observed. Whereas for $^{133}$Cs~-$^{87}$Rb TBEC we report a bifurcation of the softened Kohn mode at the point of transition from miscible to immiscible domain. The lower energy mode, after the bifurcation, goes soft and becomes a new Goldstone mode of the system.