13ª Semana Integrada do Instituto de Física de São Carlos

Dimensional crossover in Fermi gases with attractive interactions

21 de ago. de 2023 14:00

1h 30m

Salão de Eventos USP

Prêmio YPM 14h00 - 15h30

Descrição

Strongly-correlated systems are present in many phenomena in physics. From superconductors in condensed matter to superfluids in atomic physics, many-body strongly-interacting systems appear in several areas. The union of Bardeen-Cooper-Schrieffer (BCS) and Bose-Einstein condensates (BEC) theories, which were once distinct paradigms, led to a better understanding of superconductivity and superfluidity: the so-called BCS-BEC crossover. (1) At the two-body level in three dimensions (3D), the interaction between two particles may lead to a bound state if the attractive potential is strong enough to bind them. In the context of a superfluid Fermi gas, this is called the BEC regime of bosonic dimers. On the other hand, for weak attractions, the superfluid phase is characterized by the formation of weakly-coupled Cooper pairs, the BCS regime. Between them lies the most strongly-interacting region of the entire crossover, the unitary regime. Controlling the interparticle interactions is the first step in investigating the BCS-BEC crossover. In cold atoms experiments, this is achieved with a technique known as Feshbach resonances. Numerically, we modeled the interactions using a short-range microscopic potential which can be tuned to reproduce the desired scattering length and effective range. (2) We continuously varied the interaction strength of different potentials to analyze the behavior of the scattering length. Regarding the dimensionality aspects, the crossover has been realized in three and two dimensions (2D). We propose to investigate a two-component Fermi gas when the dimensionality is varied from 3D to 2D with Quantum Monte Carlo (QMC) methods, which have been successfully applied to many strongly-interacting systems, including cold Fermi gases in the crossover. (3) We will introduce an external confining potential to reduce the size of the system in one direction. The system will eventually be in a quasi-2D regime as the external potential strength increases. This topic has important applications in cold atom systems and nuclear physics.

Referências

1 RANDERIA, M.; TAYLOR, E. Crossover from Bardeen-Cooper-Schrieffer to Bose-Einstein condensation and the unitary Fermi gas. Annual Review of Condensed Matter Physics, v. 5, p. 209-232, Mar. 2014.

2 MACÊDO-LIMA, M.; MADEIRA, L. Scattering length and effective range of microscopic two-body potentials. 2023. DOI:
https://doi.org/10.48550/arXiv.2303.04591.

3 ASTRAKHARCHIK, G. E. et al. Equation of state of a Fermi gas in the BEC-BCS crossover: a quantum Monte Carlo study. Physical Review Letters, v. 93, n. 20, p. 200404-1-200404-4, Nov. 2004.