Spin conductivity spectrum and spin superfluidity in a binary Bose mixture

TL;DR

This paper analytically studies the spin conductivity spectrum in a binary Bose-Einstein condensate, revealing power-law behavior at low frequencies and the emergence of spin superfluidity, with implications for measuring drag density.

Contribution

It provides an analytical calculation of the spin conductivity spectrum and Drude weight in a binary BEC, highlighting the effects of phase transitions on these properties.

Findings

Power-law behavior of spin conductivity at low frequency.

Finite spin Drude weight indicating spin superfluidity.

Modification of spectrum at phase transition points.

Abstract

We investigate the spectrum of spin conductivity for a miscible two-component Bose-Einstein condensate (BEC) that exhibits spin superfluidity. By using the Bogoliubov theory, the regular part being the spin conductivity at finite ac frequency and the spin Drude weight characterizing the delta-function peak at zero frequency are analytically computed. We demonstrate that the spectrum exhibits a power-law behavior at low frequency, reflecting gapless density and spin modes specific to the binary BEC. At the phase transition points into immiscible and quantum-droplet states, the change in quasiparticle dispersion relations modifies the power law. In addition, the spin Drude weight becomes finite, indicating zero spin resistivity due to spin superfluidity. Our results also suggest that the Andreev-Bashkin drag density is accessible by measuring the spin conductivity spectrum.