Topological Lifshitz Transitions, Orbital Currents, and Interactions in Low-dimensional Fermi Gases in Synthetic Gauge Fields

Abstract

Low-dimensional systems of interacting fermions in a synthetic gauge field have been experimentally realized using two-component ultra-cold Fermi gases in optical lattices. Using a two-leg ladder model that is relevant to these experiments, we have studied the signatures of topological Lifshitz transitions and the effects of the inter-species interaction $U$ on the gauge-invariant orbital current in the regime of large intra-leg hopping $\Omega$. Focusing on non-insulating regimes, we have carried out numerically exact density-matrix renormalization-group (DMRG) calculations to compute the orbital current at fixed particle number as a function of the interaction strength and the synthetic gauge flux per plaquette. Signatures of topological Lifshitz transitions where the number Fermi points changes are found to persist even in the presence of very strong repulsive interactions. This numerical observation suggests that the orbital current can be captured by an appropriately renormalized mean-field band structure, which is also described here. Quantitative agreement between the mean-field and the DMRG results in the intermediate interaction regime where $U\lesssim \Omega$ is demonstrated. We also have observed that interactions can change the sign of the current susceptibility at zero field and induce Lifshitz transitions between two metallic phases, which is also captured by the mean-field theory. Correlation effects beyond mean-field theory in the oscillations of the local inter-leg current are also reported. We argue that the observed robustness against interactions makes the orbital current a good indicator of the topological Lifshitz transitions.

18 pages, 16 figures; v2: typos corrected and references updated

References in corpus (8)

• Measuring the Chern number of Hofstadter bands with ultracold bosonic atoms
• The ALPS project release 1.3: open source software for strongly correlated systems
• Bosonizing one-dimensional cold atomic gases
• New Trends in Density Matrix Renormalization
• Synthetic dimensions and spin-orbit coupling with an optical clock transition
• Diamagnetism of doped two-leg ladders and probing the nature of their commensurate phases
• Magnetic Lifshitz transition and its consequences in multi-band iron-based superconductors
• Scaling of entanglement entropy across Lifshitz transitions