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.

Original version, full text published online in Nature Physics

References in corpus (13)

• Using photoemission spectroscopy to probe a strongly interacting Fermi gas
• Amplitude / Higgs Modes in Condensed Matter Physics
• Thermodynamics of the BCS-BEC crossover
• Quantum Fluctuations in the Superfluid State of the BCS-BEC Crossover
• Determination of the Superfluid Gap in Atomic Fermi Gases by Quasiparticle Spectroscopy
• Bragg spectroscopy of a strongly interacting Fermi gas
• BCS-BEC crossover at finite temperature in the broken-symmetry phase
• Determination of the Fermion Pair Size in a Resonantly Interacting Superfluid
• The critical velocity in the BEC-BCS crossover
• Polarization Measurements and the Pairing Gap in the Universal Regime
• Dynamic spin response of a strongly interacting Fermi gas
• Induced interactions in a superfluid Bose-Fermi mixture
• 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 (40)

• Higgs mode in a strongly interacting fermionic superfluid
• 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
• Superfluid Fermi atomic gas as a quantum simulator for the study of neutron-star equation of state
• Universal van der Waals Force Between Heavy Polarons in Superfluids
• Dynamical structure factors of a two-dimensional Fermi superfluid within random phase approximation
• Resonant pair-exchange scattering and BCS-BEC crossover in a system composed of dispersive and heavy incipient bands: a Feshbach analogy
• Collective excitations of superfluid Fermi gases near the transition temperature
• 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
• Dynamic structure factor of one-dimensional Fermi superfluid with spin-orbit coupling
• Analytic normal mode frequencies for N identical particles: The microscopic dynamics underlying the emergence and stability of excitation gaps from BCS to unitarity
• Probing Goldstino excitation through the tunneling transport in a Bose-Fermi mixture with explicitly broken supersymmetry
• Dynamical effects on superconductivity in BCS-BEC crossover
• Three-body contact for fermions. I. General relations
• BCS-BCS crossover between atomic and molecular superfluids in a Bose-Fermi mixture
• Dynamic structure factor of two-dimensional Fermi superfluid with Rashba spin-orbit coupling
• Dominant Andreev Reflection through Nonlinear Radio-Frequency Transport
• Collective excitations of a charged Fermi superfluid in the BCS-BEC crossover
• Structure factors and quantum geometry in multiband BCS superconductors
• Mediated Interactions and Damping Effects in Superfluid Mixtures of Bose and Fermi Gases
• Emergence of Sound in a Tunable Fermi Fluid
• A universal pairing gap measurement proposal by dynamical excitations in 2D doped attractive Fermi-Hubbard model with spin-orbit coupling
• Isothermal compressibility and effects of multi-body molecular interactions in a strongly interacting ultracold Fermi gas
• 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
• Hybridization of the amplitude mode in a confined fermionic superfluid
• Measurement of the $s$-wave scattering length between metastable helium isotopes
• Spectrum of density, spin and pairing fluctuations of an attractive two-dimensional Fermi gas
• Low-Lying Collective Excitations of Superconductors and Charged Superfluids
• Linear response of a superfluid Fermi gas inside its pair-breaking continuum
• Resonantly enhanced superconductivity mediated by spinor condensates
• Resonant superfluidity in the Rabi-coupled spin-dependent Fermi-Hubbard model
• Novel dynamical excitations and roton-based measurement of Cooper-pair momentum in a two-dimensional Fulde-Ferrell-Larkin-Ovchinnikov superfluid on optical lattices
• A model study on superfluidity of a unitary Fermi gas of atoms interacting with a finite-ranged potential
• Probing Bardeen-Cooper-Schrieffer pairing and quasiparticle formation in ultracold gases by Rydberg atom spectroscopy
• Local energy density functional for superfluid Fermi gases from effective field theory
• Quasiparticle disintegration in fermionic superfluids