Few-to-many particle crossover of pair excitations in a superfluid
| Autor: | Resare, Fabian, Hofmann, Johannes |
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| Rok vydání: | 2022 |
| Předmět: | |
| Druh dokumentu: | Working Paper |
| Popis: | Motivated by recent advances in the creation of few-body atomic Fermi gases with attractive interactions, we study theoretically the few-to-many particle crossover of pair excitations, which for large particle numbers evolve into modes describing amplitude fluctuations of the superfluid order parameter (the "Higgs" modes). Our analysis is based on a Richardson-type pairing model that captures interactions between time-reversed fermion pairs. The model is integrable, which allows a systematic quantitative study of the few-to-many particle crossover with only minor numerical effort. We first establish a parity effect in the ground state energy, which is quantified by a so-called Matveev-Larkin parameter that generalizes the pairing gap to mesoscopic ensembles and which behaves quantitatively differently in a few-body and a many-body regime. The crossover point for this quantity is widely tunable as a function of interaction strength. We then compute the excitation spectrum and demonstrate that the pair excitation energy shows a minimum that deepens with increasing particle number and shifts to smaller interaction strengths, consistent with the finite-size precursor of a quantum phase transition to a superfluid state. We extract a critical finite-size scaling exponent that characterizes the decrease of the gap with increasing particle number. Comment: 6 pages, 5 figures |
| Databáze: | arXiv |
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