Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session F21: Precision Many-Body Physics I: Methods and Algorithms
11:30 AM–2:30 PM,
Tuesday, March 16, 2021
Sponsoring
Units:
DCOMP DCMP DAMOP
Chair: Joaquin Drut, University of North Carolina at Chapel Hill
Abstract: F21.00003 : High-order expansion around BCS theory
11:54 AM–12:06 PM
Live
Presenter:
Félix Werner
(LKB, Ecole Normale Supérieure)
Authors:
Gabriele Spada
(LKB, Ecole Normale Supérieure)
Riccardo Rossi
(CCQ, Flatiron Institute)
Fedor Simkovic
(CPHT, Ecole Polytechnique & Collège de France)
Renaud Garioud
(CPHT, Ecole Polytechnique & Collège de France)
Michel Ferrero
(CPHT, Ecole Polytechnique & Collège de France)
Kris Van Houcke
(LPENS, Ecole Normale Supérieure)
Félix Werner
(LKB, Ecole Normale Supérieure)
We report first results inside the superfluid phase of the attractive Hubbard model. Expanding around the BCS Hamiltonian, we sum up all diagrams up to order ~12 thanks to the connected determinant algorithm [1]. Working on the BCS side of the strongly correlated regime, we observe convergence of the expansion. We benchmark our results against determinant diagrammatic Monte Carlo [2] in the unpolarized regime. In the polarized regime, we accurately locate the first-order superfluid-to-normal phase transition. We also find that the expansion has a non-exponential large-order behavior associated to peculiar singularities as a function of the formal expansion parameter xi, one of them coming from the Goldstone mode and another one from a first order transition as a function of xi.
[1] R. Rossi, PRL 119, 045701 (2017).
[2] E. Burovski et al., PRL 96, 160402 (2006).
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