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Institute for Condensed Matter Theory Seminar: "Finite-temperature precision many-body calculations of the unitary Fermi gas with lattice auxiliary-field quantum Monte Carlo"

Event Type
The Institute for Condensed Matter Theory
ESB 190
Oct 11, 2021   12:00 pm  
Scot Jensen, U of Illinois Urbana Champaign
Janice Benner
Originating Calendar
Physics - Institute for Condensed Matter Theory Seminar

The unitary Fermi gas (UFG) is a system of spin-1/2 particles interacting with attractive short-range interactions, occurring in the middle of the Bardeen-Cooper-Schrieffer (BCS) to Bose-Einstein condensate (BEC) crossover where the s-wave scattering length diverges. This system has many interesting properties, including a high critical temperature for superfluidity Tc (in units of the Fermi temperature TF), and serves as a paradigm model of strongly correlated Fermi superfluids. The UFG also shows a pseudogap regime in which pairing correlations persist for temperatures above Tc and below a pairing temperature scale T*. In recent decades there has been a significant theoretical effort to obtain reliable calculations allowing for comparison with precision ultracold Fermi gas experiments. Obtaining accurate calculations for the UFG has proven difficult. In this talk I will focus on recent quantum Monte Carlo developments on two questions that have generated considerable debate for the UFG: first, the extent of the pseudogap regime; second is the temperature dependence of Tan’s contact which is a fundamental quantity of short-range interacting gases. To address these problems, we have developed lattice finite-temperature auxiliary-field quantum Monte Carlo methods in the canonical ensemble. I will show recent and new results, built on algorithmic advances and a significant computational effort, for the spin susceptibility, condensate fraction, the contact, and canonical ensemble energy-staggering pairing gaps of the UFG.

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