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arXiv:1903.06759 · Physical Review A

Coupled superfluidity of binary Bose mixtures in two dimensions

Volker Karle, Nicolò Defenu, Tilman Enss

Published Jun 28, 2019• 27 citations
arXivHTMLPDF

Abstract

The superfluidity properties of a two-component bosonic mixture with short-range repulsive interactions are investigated. The results suggest that the presence of different topological excitations can lead to coupled superfluidity in both components, with both critical temperatures locked to a unique value.
DOI
10.1103/physreva.99.063627

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While quantum fluctuations in binary mixtures of bosonic atoms with short-range interactions can lead to the formation of a self-bound droplet, for equal intracomponent interactions but an unequal number of atoms in the two components, there is an excess part that cannot bind to the droplet. Imposing confinement, as here through periodic boundary conditions in a one-dimensional setting, the droplet becomes amalgamated with a residual condensate. The rotational properties of this compound system reveal simultaneous rigid-body and superfluid behavior in the ground state and uncover that the residual condensate can carry angular momentum even in the absence of vorticity. In contradiction to the intuitive idea that the superfluid fraction of the system would be entirely made up of the excess atoms not bound by the droplet, we find evidence that this fraction is higher than what one would expect in such a picture. Our findings are corroborated by an analysis of the elementary excitations in the system, and shed new light on the coexistence of localization and superfluidity.
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Using the effective action formalism, we investigate collective excitations of a dilute mixture of a Bose gas and a two component Fermi gas when both bosons and fermions have undergone superfluid transitions. We show that there is a repulsion between Bogoliubov and Anderson modes, which has important implications including disappearance of boson superfluidity. We derive an analytic expression for the long-wavelength dispersion relation of the mixture at zero temperature and give a condition for the instability. We also numerically calculate the damping rate due to boson-fermion interaction at finite temperatures and show that the two modes are stable at sufficiently low temperatures.
Abstract A three-component bosonic mixture is capable of demonstrating a significantly rich phase diagram in comparison with a two-component mixture or a single-component fluid. With experimental studies of multi-component mixtures gaining momentum and comparatively few theoretical efforts, we consider an interacting three-component Bose gas on a lattice and, via a strong coupling expansion of the Bose–Hubbard model, look into a variety of situations, such as the intraspecies and intraspecies interactions being the same and different, attractive and repulsive, etc. A scenario of rich phase diagrams emerges where one species of atoms can be in the superfluid phase while the other two may be in insulating phases. Such a mixed-phase diagram with different species coexisting in different phases is an exciting one: a possibility that can be explored in experiments. Numerical solution of the mean field equations has further demonstrated the occurrence of insulating phases with fractional filling of each species of atoms. Such insulating phases with fractional occupancies are counterintuitive in the context of incompressible phases.