Goldstone mode and pair-breaking excitations in atomic Fermi superfluids

Abstract

Spontaneous symmetry breaking is a central paradigm of elementary particle physics, magnetism, superfluidity and superconductivity. According to Goldstone's theorem, phase transitions that break continuous symmetries lead to the existence of gapless excitations in the long-wavelength limit. These Goldstone modes generally dominate the low-energy excitations, showing that symmetry breaking has a profound impact on the physical properties of matter. Here, we present the first comprehensive study of the elementary excitations in a homogeneous strongly interacting Fermi gas through the crossover from a Bardeen-Cooper-Schrieffer (BCS) superfluid to a Bose-Einstein condensate (BEC) of molecules using two-photon Bragg spectroscopy. The spectra exhibit a discrete Goldstone mode, associated with the broken symmetry superfluid phase, as well as pair breaking single-particle excitations. Our techniques yield a direct determination of the superfluid pairing gap and speed of sound in close agreement with a strong-coupling theory.

arXiv commentOriginal version, full text published online in Nature Physics

References in corpus (27)

• Bragg spectroscopy of a Bose-Einstein condensate
• Revealing the Superfluid Lambda Transition in the Universal Thermodynamics of a Unitary Fermi Gas
• Exploring the Thermodynamics of a Universal Fermi Gas
• Using photoemission spectroscopy to probe a strongly interacting Fermi gas
• The Unitary Fermi Gas: From Monte Carlo to Density Functionals
• Amplitude / Higgs Modes in Condensed Matter Physics
• Thermodynamics of the BCS-BEC crossover
• The Excitation Spectrum of a Bose-Einstein Condensate
• Quantum Fluctuations in the Superfluid State of the BCS-BEC Crossover
• Inelastic X-ray Scattering by Electronic Excitations in Solids at High Pressure
• Collective mode of homogeneous superfluid Fermi gases in the BEC-BCS crossover
• Determination of the Superfluid Gap in Atomic Fermi Gases by Quasiparticle Spectroscopy
• Bragg spectroscopy of a strongly interacting Fermi gas
• Evolution from BCS Superconductivity to Bose Condensation: Analytic Results for the crossover in three dimensions
• Bulk and Collective Properties of a Dilute Fermi Gas in the BCS-BEC Crossover
• BCS-BEC crossover at finite temperature in the broken-symmetry phase
• Determination of the Fermion Pair Size in a Resonantly Interacting Superfluid
• Thermodynamics of an attractive 2D Fermi gas
• The critical velocity in the BEC-BCS crossover
• Momentum transferred to a trapped Bose-Einstein condensate by stimulated light scattering
• Polarization Measurements and the Pairing Gap in the Universal Regime
• Low energy Collective Modes of a Superfluid Trapped atomic Fermi Gas
• Dynamic spin response of a strongly interacting Fermi gas
• Induced interactions in a superfluid Bose-Fermi mixture
• Concavity of the collective excitation branch of a Fermi gas in the BEC-BCS crossover
• Strong-coupling corrections to ground-state properties of a superfluid Fermi gas
• Single-particle spectral density of the unitary Fermi gas: Novel approach based on the operator product expansion, sum rules and the maximum entropy method

Cited by in corpus (74)

• The low-energy Goldstone mode in a trapped dipolar supersolid
• The Fulde-Ferrell-Larkin-Ovchinnikov state for ultracold fermions in lattice and harmonic potentials: a review
• Higgs mode in a strongly interacting fermionic superfluid
• Universal Sound Diffusion in a Strongly Interacting Fermi Gas
• Beyond Lee-Huang-Yang description of self-bound Bose mixtures
• Excitation Spectrum and Superfluid Gap of an Ultracold Fermi Gas
• Contact and sum-rules in a near-uniform Fermi gas at unitarity
• Induced $p$-wave pairing in Bose-Fermi mixtures
• Tunneling transport of unitary fermions across the superfluid transition
• Measurement of the Dynamical Structure Factor of a 1D Interacting Fermi Gas
• Parametric excitation of an optically silent Goldstone-like phonon mode
• Superfluid Fermi atomic gas as a quantum simulator for the study of neutron-star equation of state
• Pair-Breaking Collective Branch in BCS Superconductors and Superfluid Fermi Gases
• Entanglement between pairing and screening in the Gorkov-Melik-Barkhudarov correction to the critical temperature throughout the BCS-BEC crossover
• Thermal crossover, transition, and coexistence in Fermi polaronic spectroscopies
• Gap equation with pairing correlations beyond mean field and its equivalence to a Hugenholtz-Pines condition for fermion pairs
• Pairing correlations across the superfluid phase transition in the unitary Fermi gas
• Emergence of a pseudogap in the BCS-BEC crossover
• Spontaneous symmetry breaking and Nambu-Goldstone modes in open classical and quantum systems
• High Frequency Sound in a Unitary Fermi Gas
• The pseudogap regime in the unitary Fermi gas
• Universal van der Waals Force Between Heavy Polarons in Superfluids
• Phononic collective excitations in superfluid Fermi gases at nonzero temperatures
• Low-momentum dynamic structure factor of a strongly interacting Fermi gas at finite temperature: The Goldstone phonon and its Landau damping
• Dynamical structure factors of a two-dimensional Fermi superfluid within random phase approximation
• Low-momentum dynamic structure factor of a strongly interacting Fermi gas at finite temperature: A two-fluid hydrodynamic description
• Resonant pair-exchange scattering and BCS-BEC crossover in a system composed of dispersive and heavy incipient bands: a Feshbach analogy
• Absorption and emission of a collective excitation by a fermionic quasiparticle in a Fermi superfluid
• Precursor of Superfluidity in a Strongly Interacting Fermi Gas with Negative Effective Range
• Collective excitations of superfluid Fermi gases near the transition temperature
• Role of Nambu-Goldstone modes in the fermionic superfluid point contact
• Sound propagation in a two-dimensional Bose gas across the superfluid transition
• Effects of quantum fluctuations on the low-energy collective modes of two-dimensional superfluid Fermi gases from the BCS to the Bose Limit
• Exciting the Higgs mode in a strongly-interacting Fermi gas by interaction modulation
• Energy absorption spectroscopy of unitary Fermi gases in a uniform potential
• Dynamic structure factors of a strongly interacting Fermi superfluid near an orbital Feshbach resonance across the phase transition from BCS to Sarma superfluid
• Beyond mean-field corrections to the quasiparticle spectrum of superfluid Fermi gases
• Dynamic structure factor of one-dimensional Fermi superfluid with spin-orbit coupling
• Renormalization of the superfluid density in the two-dimensional BCS-BEC crossover
• Transport of Spin and Mass at Normal-Superfluid Interfaces in the Unitary Fermi Gas
• Dynamical effects on superconductivity in BCS-BEC crossover
• Probing Goldstino excitation through the tunneling transport in a Bose-Fermi mixture with explicitly broken supersymmetry
• Analytic normal mode frequencies for N identical particles: The microscopic dynamics underlying the emergence and stability of excitation gaps from BCS to unitarity
• Transition from supersonic to subsonic waves in superfluid Fermi gases
• Structure factors and quantum geometry in multiband BCS superconductors
• BCS-BCS crossover between atomic and molecular superfluids in a Bose-Fermi mixture
• Collective excitations of a charged Fermi superfluid in the BCS-BEC crossover
• Dynamic structure factor of two-dimensional Fermi superfluid with Rashba spin-orbit coupling
• Dominant Andreev Reflection through Nonlinear Radio-Frequency Transport
• The linear Dirac spectrum and the Weyl states in the Drude-Sommerfeld topological model
• Three-body contact for fermions. I. General relations
• Emergence of Sound in a Tunable Fermi Fluid
• Isothermal compressibility and effects of multi-body molecular interactions in a strongly interacting ultracold Fermi gas
• A universal pairing gap measurement proposal by dynamical excitations in 2D doped attractive Fermi-Hubbard model with spin-orbit coupling
• Damping of the Anderson-Bogolyubov mode by spin and mass imbalance in Fermi mixtures
• Tuning Dissipation and Excitations in Superfluid Fermi Gases with a Moving Impurity
• Mediated Interactions and Damping Effects in Superfluid Mixtures of Bose and Fermi Gases
• Higgs and Nambu-Goldstone modes in condensed matter physics
• Spin-dipole mode in a trapped Fermi gas near unitarity
• Dynamical structure factor and a new method to measure the pairing gap in two-dimensional attractive Fermi-Hubbard model
• Spectrum of density, spin and pairing fluctuations of an attractive two-dimensional Fermi gas
• Hybridization of the amplitude mode in a confined fermionic superfluid
• Measurement of the $s$-wave scattering length between metastable helium isotopes
• Low-Lying Collective Excitations of Superconductors and Charged Superfluids
• Bragg spectroscopy and pair-breaking-continuum mode in a superfluid Fermi gas
• Resonantly enhanced superconductivity mediated by spinor condensates
• Linear response of a superfluid Fermi gas inside its pair-breaking continuum
• Small amplitude collective modes of a finite-size unitary Fermi gas in deformed traps
• Probing Bardeen-Cooper-Schrieffer pairing and quasiparticle formation in ultracold gases by Rydberg atom spectroscopy
• Novel dynamical excitations and roton-based measurement of Cooper-pair momentum in a two-dimensional Fulde-Ferrell-Larkin-Ovchinnikov superfluid on optical lattices
• Resonant superfluidity in the Rabi-coupled spin-dependent Fermi-Hubbard model
• Quasiparticle disintegration in fermionic superfluids
• A model study on superfluidity of a unitary Fermi gas of atoms interacting with a finite-ranged potential
• Local energy density functional for superfluid Fermi gases from effective field theory