Two-superfluid Model of Two-component Bose-Einstein Condensates; First Sound and Second Sound

Superfluid \(^4\)He at a finite temperature is described by the two-fluid model with the normal fluid component and the superfluid component.We formulate the two-fluid model for two-component BECs, namely two-superfluid model, starting from the coupled Gross-Pitaevskii equations.The two-superfluid model well corresponds to the two-fluid model in superfluid \(^4\)He.In a special condition, the two sound modes in the two-superfluid model behave like first and second sounds in the two-fluid model of superfluid \(^4\)He.