Imbalanced Fermi Gases at Unitarity

Abstract

We consider imbalanced Fermi gases with strong attractive interactions, for which Cooper-pair formation plays an important role. The two-component mixtures consist either of identical fermionic atoms in two different hyperfine states, or of two different atomic species both occupying only a single hyperfine state. In both cases, the number of atoms for each component is allowed to be different, which leads to a spin imbalance, or spin polarization. Two different atomic species also lead to a mass imbalance. Imbalanced Fermi gases are relevant to condensed-matter physics, nuclear physics and astroparticle physics. They have been studied intensively in recent years, following their experimental realization in ultracold atomic Fermi gases. The experimental control in such a system allows for a systematic study of the equation of state and the phase diagram as a function of temperature, spin polarization and interaction strength. In this review, we discuss the progress in understanding strongly-interacting imbalanced Fermi gases, where a main goal is to describe the results of the highly controlled experiments. We start by discussing Feshbach resonances, after which we treat the imbalanced Fermi gas in mean-field theory to give an introduction to the relevant physics. We encounter several unusual superfluid phases, including phase separation, gapless Sarma superfluidity, and supersolidity. To obtain a more quantitative description of the experiments, we review also more sophisticated techniques, such as diagrammatic methods and the renormalization-group theory. We end the review by discussing two theoretical approaches to treat the inhomogeneous imbalanced Fermi gas, namely the Landau-Ginzburg theory and the Bogoliubov-de Gennes approach.

108 pages, 30 figures. Textual changes and references added

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• Exact evolution equation for the effective potential
• Theory of ultracold Fermi gases
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• Direct observation of Anderson localization of matter-waves in a controlled disorder
• Non-equilibrium coherence dynamics in one-dimensional Bose gases
• Observation of Fermi Polarons in a Tunable Fermi Liquid of Ultracold Atoms
• Weakly bound dimers of fermionic atoms
• Collective excitations of a degenerate gas at the BEC-BCS crossover
• A Bose-Einstein Condensate in a Uniform Light-induced Vector Potential
• Strong dipolar effects in a quantum ferrofluid
• Observation of Phase Separation in a Strongly-Interacting Imbalanced Fermi Gas
• Molecular Probe of Pairing in the BEC-BCS Crossover
• Resonantly-paired fermionic superfluids
• Thermodynamics of the BCS-BEC crossover
• Direct Observation of the Superfluid Phase Transition in Ultracold Fermi Gases
• Phase diagram of a two-component Fermi gas with resonant interactions
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• Deformation of a Trapped Fermi Gas with Unequal Spin Populations
• Normal state of a polarized Fermi gas at unitarity
• Quantum degenerate two-species Fermi-Fermi mixture coexisting with a Bose-Einstein condensate
• Critical Temperature and Thermodynamics of Attractive Fermions at Unitarity
• Dislocations and vortices in pair density wave superconductors
• Phase diagram of a strongly interacting polarized Fermi gas in one dimension
• Quantum Fluctuations in the Superfluid State of the BCS-BEC Crossover
• Ultra-cold Polarized Fermi Gases
• BEC-BCS crossover, phase transitions and phase separation in polarized resonantly-paired superfluids
• p-wave Feshbach molecules
• Epsilon expansion for a Fermi gas at infinite scattering length
• Equation of state of a superfluid Fermi gas in the BCS-BEC crossover
• Normal state of highly polarized Fermi gases: Full many-body treatment
• Virial expansion for a strongly correlated Fermi gas
• Quantum Monte Carlo Simulations of the BCS-BEC Crossover at Finite Temperature
• Ultracold Heteronuclear Fermi-Fermi Molecules
• Measurement of the Entropy and Critical Temperature of a Strongly Interacting Fermi Gas
• Phase diagram of a cold polarized Fermi gas
• Vortex proliferation in the Berezinskii-Kosterlitz-Thouless regime on a two-dimensional lattice of Bose-Einstein condensates
• Two-species fermion mixtures with population imbalance
• A Unitary Fermi Supersolid: The Larkin-Ovchinnikov Phase
• Density-Matrix Renormalization Group Study of Trapped Imbalanced Fermi Condensates
• Induced P-wave Superfluidity in Asymmetric Fermi Gases
• Large-N expansion for unitary superfluid Fermi gases
• Generic Phase Diagram of Fermion Superfluids with Population Imbalance
• Critical Temperature Curve in the BEC-BCS Crossover
• Flow Equations for the BCS-BEC Crossover
• Surface Tension in Unitary Fermi Gases with Population Imbalance
• Zero Temperature Thermodynamics of Asymmetric Fermi Gases at Unitarity
• Polarization Measurements and the Pairing Gap in the Universal Regime
• Polarized Fermi condensates with unequal masses: Tuning the tricritical point
• Larkin-Ovchinnikov state in resonant Fermi gas
• Thermodynamics of balanced and slightly spin-imbalanced Fermi gases at unitarity
• Renormalization Group Theory for the Imbalanced Fermi Gas
• BEC-BCS Crossover of a Trapped Two-Component Fermi Gas with Unequal Masses
• Heavy-Light Fermion Mixtures at Unitarity
• Resonant pairing between Fermions with unequal masses
• Mean field thermodynamics of a spin-polarized spherically trapped Fermi gas at unitarity
• Mixtures of ultracold fermions with unequal masses
• The role of interactions in spin-polarised atomic Fermi gases at unitarity
• Unitary Fermi gas at finite temperature in the epsilon expansion
• Renormalization of the BCS-BEC crossover by order parameter fluctuations
• Breakdown of the local density approximation in interacting systems of cold fermions in strongly anisotropic traps
• Normal-Superfluid Interface Scattering For Polarized Fermion Gases
• Popov approximation for composite bosons in the BCS-BEC crossover
• Detecting the breached pair phase in a polarized ultracold Fermi gas
• Non-BCS superfluidity in trapped ultracold Fermi gases
• Small mass- and trap-imbalanced two-component Fermi systems
• Ultracold polarized Fermi gas at intermediate temperatures
• Population imbalanced fermions in harmonically trapped optical lattices
• Induced p-wave superfluidity in strongly interacting imbalanced Fermi gases
• Normal-Superfluid Interface for Polarized Fermion Gases

Cited by in corpus (73)

• Polarons, Dressed Molecules, and Itinerant Ferromagnetism in ultracold Fermi gases
• Field-induced superconducting phase of FeSe in the BCS-BEC cross-over
• BCS-BEC Crossover and the Unitary Fermi Gas
• The BCS-BEC crossover: From ultra-cold Fermi gases to nuclear systems
• The Fulde-Ferrell-Larkin-Ovchinnikov state for ultracold fermions in lattice and harmonic potentials: a review
• Density and isospin asymmetry dependence of high-momentum components
• Production of a degenerate Fermi-Fermi mixture of dysprosium and potassium atoms
• Mediated interactions between Fermi polarons and the role of impurity quantum statistics
• Pseudogaps in strongly interacting Fermi gases
• Gapless topological Fulde-Ferrell superfluidity in spin-orbit coupled Fermi gases
• Phase structure of mass- and spin-imbalanced unitary Fermi gases
• Quantum mixtures of ultracold gases of neutral atoms
• Resonantly Interacting Fermi-Fermi Mixture of ${}^{161}$Dy and ${}^{40}$K
• Physics of ultracold Fermi gases revealed by spectroscopies
• Phase structure of spin-imbalanced unitary Fermi gases
• Finite-temperature equation of state of polarized fermions at unitarity
• Critical temperature and superfluid gap of the Unitary Fermi Gas from Functional Renormalization
• Phase Diagram of a Strongly Interacting Spin-Imbalanced Fermi Gas
• Exploring ultracold collisions in ${}^6$Li-${}^{53}$Cr Fermi mixtures: Feshbach resonances and scattering properties of a novel alkali-transition metal system
• Quasiparticle Excitations in the Superconducting State of FeSe Probed by Thermal Hall Conductivity in the Vicinity of the BCS-BEC Crossover
• Interaction quantum quenches in the one-dimensional Fermi-Hubbard model with spin imbalance
• Pairing and the spin susceptibility of the polarized unitary Fermi gas in the normal phase
• Polarized fermions in one dimension: density and polarization from complex Langevin calculations, perturbation theory, and the virial expansion
• Tunneling and Fluctuating Electron-Hole Cooper Pairs in Double Bilayer Graphene
• Fulde-Ferrell superfluidity in ultracold Fermi gases with Rashba spin-orbit coupling
• Sarma phase in relativistic and non-relativistic systems
• Stable solvers for real-time Complex Langevin
• A strongly interacting Sarma superfluid near orbital Feshbach resonances
• Pairing patterns in one-dimensional spin- and mass-imbalanced Fermi gases
• Double-degenerate Fermi mixtures of ${}^6$Li and ${}^{53}$Cr atoms
• Observation of low-field Feshbach resonances between ${}^{161}$Dy and ${}^{40}$K
• Quantum Lifshitz points and fluctuation-induced first-order phase transitions in imbalanced Fermi mixtures
• Observation of Feshbach resonances in an ${}^{167}$Er-${}^6$Li Fermi-Fermi mixture
• Phases of spin- and mass-imbalanced ultracold Fermi gases in harmonic traps
• Larkin-Ovchinnikov phases in two-dimensional square lattices
• Dimensional Crossover in a Spin-imbalanced Fermi gas
• Optically trapped Feshbach molecules of fermionic 161Dy and 40K
• Disordered structures in ultracold spin-imbalanced Fermi gas
• Tan's contact and the phase distribution of repulsive Fermi gases: Insights from QCD noise analyses
• Prospects of forming high-spin polar molecules from ultracold atoms
• Quantum Coherent States of Interacting Bose-Fermi Mixtures in One Dimension
• Multiple phase separation in one-dimensional mixtures of mass- and population-imbalanced attractive Fermi gases
• Pairing patterns in polarized unitary Fermi gases above the superfluid transition
• One-dimensional repulsive Hubbard model with mass imbalance: Orders and filling anomaly
• Effective potential and quantum criticality for imbalanced Fermi mixtures
• Measurement of the dynamic polarizability of Dy atoms near the 626-nm intercombination line
• Feasibility of a Fulde-Ferrell-Larkin-Ovchinnikov superfluid Fermi atomic gas
• Unconventional superconductivity of an altermagnetic metal: Polarized BCS and inhomogeneous Fulde-Ferrell-Larkin-Ovchinnikov states
• Fulde-Ferrell-Larkin-Ovchinnikov state in bilayer dipolar systems
• Application of renormalized RPA to polarized Fermi gases
• Towards a field-theory interpretation of bottom-up holography
• Spin-imbalanced ultracold Fermi gases in a two-dimensional array of tubes
• Transport of Spin and Mass at Normal-Superfluid Interfaces in the Unitary Fermi Gas
• BCS-BCS crossover between atomic and molecular superfluids in a Bose-Fermi mixture
• Towards sampling complex actions
• Larkin-Ovchinikov superfluidity in time-reversal symmetric bilayer Fermi gases
• Low-energy modes of spin-imbalanced Fermi gases in BCS phase
• Exploring ${}^3{P}_0$ Superfluid in Dilute Spin-Polarized Neutron Matter
• Engineering nonequilibrium superconducting phases in a voltage-driven superconductor under an external magnetic field
• Leading Order $k_{F}a$ Corrections to the Free Energy and Phase Separation in Two-component Fermion Systems
• Dipole-Mode Spectrum and Hydrodynamic Crossover in a Resonantly Interacting Two-Species Fermion Mixture
• In-medium bound-state formation and inhomogeneous condensation in Fermi gases in a hard-wall box
• The Gor'kov and Melik-Barkhudarov correction to an imbalanced Fermi gas in the presence of impurities
• Optically trapped Feshbach molecules of fermionic ${}^{161}$Dy and ${}^{40}$K: Role of light-induced and collisional losses
• Vortex lattice in spin-imbalanced unitary Fermi gas
• A lattice pairing-field approach to ultracold Fermi gases
• Hierarchy of pairing in imbalanced three-component one-dimensional Fermi gas
• Vortices in Fermi gases with spin-dependent rotation potentials
• Topological fluctuating electron-hole Cooper pairs in graphene-GaAs heterostructures
• Low-field Feshbach resonances and three-body losses in a fermionic quantum gas of ${}^{161}$Dy
• Quantum vortex dipole as a probe of the normal component distribution
• Strong Fulde-Ferrell Larkin-Ovchinnikov pairing fluctuations in polarized Fermi systems
• Detecting inhomogeneous chiral condensation from the bosonic two-point function in the $(1+1)$-dimensional Gross-Neveu model in the mean-field approximation