Theory Talk is an informal setting for fellow NC State physicists to see and hear work currently being pursued within the department. Speakers are encouraged to talk about work in progress and exchange ideas with the audience. Faculty, postdocs, and especially graduate students are encouraged to attend and present. Interested visitors and researchers from the Triangle area are also welcome.


Lukas Rammelmueller (TU Darmstadt)
Thursday, 1:00 PM, September 27, Riddick 400P
Thermodynamics of the spin-polarized unitary Fermi gas

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 range of 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.