Single-particle properties and pseudogap effects in the BCS-BEC crossover regime of an ultracold Fermi gas above Tc

Abstract

We investigate strong-coupling effects on normal state properties of an ultracold Fermi gas. Within the framework of $T$-matrix approximation in terms of pairing fluctuations, we calculate the single-particle density of states (DOS), as well as the spectral weight, over the entire BCS-BEC crossover region above the superfluid phase transition temperature $T_{\mathrm{c}}$. Starting from the weak-coupling BCS regime, we show that the so-called pseudogap develops in DOS above $T_{\mathrm{c}}$, which becomes remarkable in the crossover region. The pseudogap structure continuously changes into a fully gapped one in the strong-coupling BEC regime, where the gap energy is directly related to the binding energy of tightly bound molecules. We determine the pseudogap temperature $T^{\ast }$ where the dip structure in DOS vanishes. The value of $T^{\ast }$ is shown to be very different from another characteristic temperature $T^{\ast \ast }$ where a BCS-type double peak structure disappears in the spectral weight. While one finds $T^{\ast }>T^{\ast \ast }$ in the BCS regime, $T^{\ast \ast }$ becomes higher than $T^{\ast }$ in the crossover region and BEC regime. Including this, we determine the pseudogap region in the phase diagram of ultracold Fermi gases. Our results would be useful in the search for the pseudogap region in ultracold ${}^6$Li and ${}^{40}$K Fermi gases.

23 pages, 11 figures

References in corpus (7)

• Many-Body Physics with Ultracold Gases
• Theory of ultracold Fermi gases
• Scanning tunneling spectroscopy of high-temperature superconductors
• Collective excitations of a degenerate gas at the BEC-BCS crossover
• Using photoemission spectroscopy to probe a strongly interacting Fermi gas
• BCS-BEC crossover at finite temperature in the broken-symmetry phase
• Bragg Spectroscopy of Cold Atomic Fermi Gases

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