Thermodynamics of the two-component Fermi gas with unequal masses at unitarity

Abstract

We consider mass-imbalanced two-component Fermi gases for which the unequal-mass atoms interact via a zero-range model potential with a diverging s-wave scattering length $a_s$, i.e., with $1/a_s=0$. The high temperature thermodynamics of the harmonically trapped and homogeneous systems are examined using a virial expansion approach up to third order in the fugacity. We find that the universal part of the third-order virial coefficient associated with two light atoms and one heavy atom is negative, while that associated with two heavy and one light atom changes sign from negative to positive as the mass ratio $\kappa$ increases, and diverges when Efimov physics sets in at $\kappa =13.61$. By examining the Helmholtz free energy, we find that the equilibrium polarization of the trapped and homogeneous systems is 0 for $\kappa =1$, but finite for $\kappa \ne 1$ (with a majority of heavy particles). Compared to the equilibrium polarization of the non-interacting system, the equilibrium polarization at unitarity is increased for the trapped system and decreased for the homogeneous system. We find that unequal-mass Fermi gases are stable for all polarizations.

14+2 pages, 14 figures

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• Path integral Monte Carlo determination of the fourth-order virial coefficient for unitary two-component Fermi gas with zero-range interactions
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• Universal clusters as building blocks of stable quantum matter
• The third virial coefficient of a two-component unitary Fermi gas across an Efimov-effect threshold
• Universal description of three two-component fermions
• Phase diagrams of Fermi gases in a trap with mass and population imbalances at finite temperature
• Ground-State Magnetization in Mixtures of a Few Ultra-Cold Fermions in One-Dimensional Traps
• Second-order virial expansion for an atomic gas in a harmonic waveguide
• Criteria of off-diagonal long-range order in Bose and Fermi systems based on the Lee-Yang cluster expansion method
• Tunable high-temperature thermodynamics of weakly-interacting dipolar gases
• Universality in rotating strongly interacting gases