Roton softening and supersolidity in Rb spinor condensates

TL;DR

This paper demonstrates that roton softening and potential supersolidity can occur in 87Rb spinor condensates due to dipolar interactions and spin dynamics, with phase diagrams illustrating various instabilities influenced by magnetic field orientation and Zeeman shift.

Contribution

It reveals the occurrence of roton softening in Rb spinor condensates considering dipolar interactions, spin dynamics, and geometry, explaining experimental observations.

Findings

Roton softening occurs in 87Rb spinor condensates with dipolar interactions.

Dynamical instabilities develop at finite wavevectors under certain conditions.

Phase diagrams show instabilities depend on magnetic field direction and quadratic Zeeman shift.

Abstract

Superfluids with a tendency towards periodic crystalline order have both a phonon and roton like spectrum of collective modes. The softening of the roton spectrum provides one route to a supersolid. We show that roton softening occurs in 87Rb spinor condensates once dipolar interactions and spin dynamics are taken into account. By including the effects of a quasi-two-dimensional geometry and rapid Larmor precession, we show a dynamical instability develops in the collective mode spectrum at finite wavevectors. We construct phase diagrams showing a variety of instabilities as a function of the direction of the magnetic field and strength of the quadratic Zeeman shift. Our results provide a possible explanation of current experiments in the Berkeley group Phys. Rev. Lett. 100:170403 (2008).