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Physical Review A

Quantum phases of multiorbital bosonic gases in a hexagonal lattice

Pengfei Zhang, Hui Ru Tan, Jianmin Yuan, Yongqiang Li

Published Sep 21, 2023• 2 citations
Publisher

Abstract

Orbital degree of freedom plays an important role for understanding quantum many-body phenomena. In this paper, we study an experimentally related setup with ultracold bosons loaded into hybridized bands of two-dimensional hexagonal optical lattices. We find that the system supports various quantum many-body phases at zero temperature, including chiral superfluid and chiral Mott insulating phases by breaking time-reversal symmetry, and the time-reversal-even insulating phase, based on dynamical mean-field theory. In the deep insulating regime, the time-reversal-even phase arises from the interplay of effective Dzyaloshinskii-Moriya and Heisenberg exchange interactions. To relate to experimental situations, we make band-structure calculations to obtain the Hubbard parameters, and show that these orbital ordering phases persist also in the presence of next-nearest-neighbor hopping.

DOI
10.1103/physreva.108.033314

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Orbital phases of ppp-band ultracold fermions in the frustrated triangular lattice
Orbital degrees of freedom play an important role for understanding the emergence of unconventional quantum phases. Ultracold atomic gases in optical lattices provide a wonderful platform to simulate orbital physics. In this work, we consider spinless fermionic atoms loaded into ppp-orbital bands of a two-dimensional frustrated triangular lattice. The system can be described by an extended Fermi-Hubbard model, which is numerically solved by using the orbital version of real-space dynamical mean-field theory. Low-temperature phase diagrams are obtained, which contain stripe-, ferro- and para-orbital ordered quantum phases, due to the interplay of anisotropic hoppings and geometrical frustration. In order to understand the underlying mechanics of competing orbital orders, we derive an effective orbital-exchange model, which yields consistent explanation with our main numerical results.
Complex lattices provide a versatile ground for fascinating quantum many-body physics. Here, we propose an exotic mechanics for generating orbital frustration in hexagonal lattices. We study two-component (pseudospin-12\frac{1}{2}21​) Bose gases in ppp-orbital bands of two-dimensional hexagonal lattices, and find that the system exhibits previously untouched orbital frustration as a result of the interplay of spin and orbital degrees of freedom, in contrast to normal Ising-type orbital ordering of spinless ppp-orbital band bosons in two-dimensional hexagonal lattices. Based on the classification by symmetry analysis, we find the interplay of orbital frustration and strong interaction leads to exotic Mott and superfluid phases with spin-orbital intertwined orders, in spite of the complete absence of spin-orbital interaction in the Hamiltonian. Our study implies many-body correlations in a multiorbital setting could induce rich spin-orbital intertwined physics in complex lattice structures.
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The orbital degree of freedom plays an important role in understanding exotic phenomena of strongly correlated materials. In this work, we study strongly correlated ultracold bosonic gases coupled to a high-finesse cavity, pumped by a blue-detuned laser in the transverse direction. By controlling the reflection of the pump laser, we find that atoms can be selectively transferred to the odd-parity ppp-orbital band or to the even-parity ddd-orbital band of a two-dimensional square lattice, accompanied by pronounced cavity-photon excitations. By interacting with the cavity field, atoms self-organize to form stable higher-orbital superfluid and Mott-insulating phases with orbital-density waves, as a result of cavity-induced orbital-flip hoppings. Our study opens a route to manipulate orbital degrees of freedom in strongly correlated quantum gases via coupling to optical cavities.