Emergence of the Unconventional Type-II Nambu-Goldstone Modes with Topological Origin in Bose Superfluids

TL;DR

This paper predicts a new class of quadratically dispersed Nambu-Goldstone modes in Bose superfluids, linking topological transitions with symmetry breaking, and proposes a detection scheme for these unconventional modes.

Contribution

It introduces a novel topologically-originated mechanism for type-II NG modes in Bose superfluids, expanding the understanding beyond traditional symmetry-based explanations.

Findings

Discovery of quadratically dispersed NG modes in mixed s and p band Bose superfluids.

Connection established between topological transitions and the emergence of these modes.

Proposed experimental detection scheme for the unconventional NG modes.

Abstract

The Nambu-Goldstone (NG) modes in a nonrelativistic system can be classified into two types from their characteristic features: being of either an odd (type I) or an even (type II) power energy-momentum dispersion. Conventionally, the type-II NG modes may universally arise from spontaneous breaking of noncommutative symmetry pairs. Here, we predict a novel type of quadratically dispersed NG modes that emerges in mixed $s$ and $p$ band Bose superfluids in an optical lattice and, unlike the conventional type-II NG modes, cannot be solely interpreted with the celebrated symmetry-based argument. Instead, we show that the existence of such modes has a profound connection to the topological transition on projective complex order-parameter space. The detection scheme is also proposed. Our Letter reveals a new universal mechanism for emergence of type-II NG modes, which bridges intrinsically the Landau symmetry-breaking and topological theories.