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Conserving Gapless Mean-Field Theory of a Multi-Component Bose-Einstein Condensate

Yoshiyuki Kondo·Takafumi Kita
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Abstract

We develop a mean-field theory for Bose-Einstein condensation of spin-1 atoms with internal degrees of freedom. It is applicable to nonuniform systems at finite temperatures with a plausible feature of satisfying the Hugenholtz-Pines theorem and various conservation laws simultaneously. Using it, we clarify thermodynamic properties and the excitation spectra of a uniform gas. The condensate is confirmed to remain in the same internal state from T=0 up to $T_{c}$ for both antiferromagnetic and ferromagnetic interactions. The excitation spectra of the antiferromagnetic (ferromagnetic) interaction are found to have only a single gapless mode, contrary to the prediction of the Bogoliubov theory where three (two) of them are gapless. We present a detailed discussion on those single-particle excitations in connection with the collective excitations.

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Yoshiyuki Kondo, Takafumi Kita. 2008-12-01. Conserving Gapless Mean-Field Theory of a Multi-Component Bose-Einstein Condensate. https://doi.org/10.1143/jpsj.76.024008

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