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Theory Seminar – Lukas Rammelmueller
September 27, 2018 | 1:00 pm - 2:00 pm
Title: Thermodynamics of the spin-polarized unitary Fermi gas
Abstract: The unitary Fermi gas, situated right in the middle of the crossover between Bardeen-Cooper-Schrieffer superfluidity and Bose-Einstein condensation, is one of the most intensely studied many-body system in recent years. However, its strongly-correlated nature renders a theoretical treatment challenging. While the spin-balanced scenario is accessible with Quantum Monte Carlo methods, its spin-imbalanced counterpart suffers from a sign problem and is thus out of reach for such approaches.
Recently, the complex Langevin method was adapted to non-relativistic theories. With this method at hand, we are now able to treat spin-polarized fermions at unitarity in an ab initio fashion and extract thermodynamic properties such as the particle density and magnetization. From equations of state we obtain response functions such as the compressibility and magnetic susceptibility. In the spin-balanced case we observe excellent agreement of our non-perturbaive results with existing state-of-the-art results from other methods as well as with experimental data. At low fugacity, we find excellent agreement with the virial expansion for spin-polarized systems. Away from the limit where the virial expansion is valid, we provide predictions for the equations of state for a wide rangeof spin asymmetries. In the fully quantum mechanical regime close to the balanced limit, our results suggest that the critical temperature for the superfluid transition depends only weakly on the spin polarization.