Dynamic structure factor of a strongly correlated Fermi superfluid within a density functional theory approach

Year: 2016

Authors: Zou P., Dalfovo F., Sharma R., Liu XJ., Hu H.

Autors Affiliation: Swinburne Univ Technol, Ctr Quantum & Opt Sci, Hawthorn, Vic 3122, Australia; Univ Trento, INO CNR BEC Ctr, Via Sommarive 14, I-38123 Povo, Italy; Univ Trento, Dipartimento Fis, Via Sommarive 14, I-38123 Povo, Italy; Tata Inst Fundamental Res, Dept Theoret Phys, Homi Bhabha Rd, Bombay 400005, Maharashtra, India

Abstract: We theoretically investigate the dynamic structure factor of a strongly interacting Fermi gas at the crossover from Bardeen-Cooper-Schrieffer superfluids to Bose-Einstein condensates, by developing an improved random phase approximation within the framework of a density functional theory (DFT)-the so-called superfluid local density approximation. Compared with the previous random-phase-approximation studies based on the standard Bogoliubov-de Gennes equations, the use of the DFT greatly improves the accuracy of the equation of state at the crossover, and leads to a better description of both collective Bogoliubov-Anderson-Goldstone phonon mode and single-particle fermionic excitations at small transferred momentum. Near unitarity, where the s-wave scattering length diverges, we show that the single-particle excitations start to significantly contribute to the spectrum of dynamic structure factor once the frequency is above a threshold of the energy gap at 2 Delta. The sharp rise in the spectrum at this threshold can be utilized to measure the pairing gap Delta. Together with the sound velocity determined from the phonon branch, the dynamic structure factor provides us some key information of the crossover Fermi superfluid. Our predictions could be examined in experiments with Li-6 or K-40 atoms using Bragg spectroscopy.

Journal/Review: NEW JOURNAL OF PHYSICS

Volume: 18      Pages from: 113044-1  to: 113044-13

KeyWords: dynamic structure factor; superfluid local density approximation; Fermi superfluid; random phase approximation
DOI: 10.1088/1367-2630/18/11/113044

Citations: 7
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