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arXiv:2101.03774

Topological semimetal and superfluid of s-wave interacting fermionic atoms in an orbital optical lattice

Maksims Arzamasovs, Shuai Li, W. Vincent Liu, Bo Liu

Published Jan 11, 2021• 0 citations
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Abstract

Recent advanced experimental implementations of optical lattices with highly tunable geometry open up new regimes for quantum many-body states of matter that previously had not been accessible. Here we introduce a symmetry-based method of utilizing the geometry of optical lattice to systematically control topologically non-trivial orbital hybridization. Such an orbital mixing leads to an unexpected and yet robust topological semimetal at single-particle level for a gas of fermionic atoms. When considering s-wave attractive interaction between atoms as for instance tuned by Feshbach resonance, topological superfluid state with high Chern number is unveiled in the presence of on-site rotation. This state supports chiral edge excitations, manifesting its topological nature. An experimental realization scheme is designed, which introduces a systematic way of achieving a new universality class (such as Chern number of 2) of orbital-hybridized topological phases beyond geometrically standard optical lattices.

DOI
10.48550/arxiv.2101.03774

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We propose a symmetry-based method of using noncentrosymmetric optical lattices to systematically control topological nontrivial orbital hybridization. A crucial difference from the previous studies is the role of inversion symmetry breaking, which is applied to induce an exotic orbital-changing hopping perpendicular to the direction without inversion symmetry and opens a band gap, instead of reducing the codimension and producing gapless points. The orbital mixing here is reminiscent of the spin-orbit physics based on hyperfine states but differs in symmetry and origin. This nontrivial orbital hybridization produces a topological band structure. Attractively interacting fermionic atoms loaded in such a lattice are found to show an orbital topological Fulde-Ferrell superfluid state in the presence of onsite rotation. This state supports Majorana fermions on its edges. Our mechanism should pave an alternative way to achieve orbital topological phases in optical lattices of nonstandard geometry.
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Weyl points exist in a fascinating topological state of matter with linear band crossings analogous to magnetic monopoles. Tremendous efforts have been devoted to investigating fermionic topological materials with Weyl points in the single-particle band dispersion. It remains elusive for realizing interaction-induced Weyl points, especially for bosons. Motivated by recent experimental progress in ultracold atoms, we propose a scheme to create Weyl points for Bogoliubov excitations of a bosonic superfluid in a three-dimensional cubic optical lattice. The unique design of the lattice leads to interaction-induced time-reversal symmetry breaking for a ppp-orbital superfluid, which in turn induces Weyl Bogoliubov excitations. Analogous to Weyl semimetals of electronic systems, the superfluid also supports topologically protected edge modes due to the bulk-boundary correspondence.