Nambu-Goldstone modes in segregated Bose-Einstein condensates

TL;DR

This paper theoretically investigates Nambu-Goldstone modes in segregated two-component Bose-Einstein condensates, revealing two distinct low-energy excitations, including an in-phase phonon and a ripplon, with potential experimental verification.

Contribution

It identifies and characterizes two Nambu-Goldstone modes in segregated BECs, including a ripplon with fractional dispersion, expanding understanding of symmetry breaking in such systems.

Findings

Existence of two Nambu-Goldstone modes: phonon and ripplon.

The ripplon exhibits fractional dispersion.

Signature of modes can be observed in harmonic traps.

Abstract

Nambu-Goldstone modes in immiscible two-component Bose-Einstein condensates are studied theoretically. In a uniform system, a flat domain wall is stabilized and then the translational invariance normal to the wall is spontaneously broken in addition to the breaking of two U(1) symmetries in the presence of two complex order parameters. We clarify properties of the low-energy excitations and identify that there exist two Nambu-Goldstone modes: in-phase phonon with a linear dispersion and ripplon with a fractional dispersion. The signature of the characteristic dispersion can be verified in segregated condensates in a harmonic potential.