Landau versus Spin Superfluidity in Spinor Bose-Einstein Condensates

TL;DR

This paper investigates spin and density excitations in spin-1/2 Bose-Einstein condensates, revealing how spin waves affect superfluidity and identifying critical velocities for superfluid breakdown.

Contribution

It provides a detailed analysis of spin wave excitation and its impact on Landau superfluidity in both ferromagnetic and antiferromagnetic spinor condensates.

Findings

Pure spin waves can be excited by local magnetic defects.

Antiferromagnetic condensates lack absolute superfluidity.

Two critical velocities exist for superfluid breakdown in ferromagnetic condensates.

Abstract

We consider a spin-1/2 Bose-Einstein condensate prepared initially in a single spin projection. The two channels of excitations existing in such a system (namely density and spin waves) are discussed and we show how pure spin waves can be excited in the presence of local magnetic defects. We analyze the role played by spin excitations on the Landau superfluidity criterion and demonstrate the absence of absolute superfluidity for the antiferromagnetic condensate. In the ferromagnetic case, we identify two critical velocities for the breakdown of superfluidity.