Ideality of fermi gases in a strong magnetic field

M. A. Ivanov, S. S. Lipovetskiǐ, V. S. Sekerzhitski

S. S. Lipovetskiǐ, A. A. Olesik, В. С. Секержицкий

Yu. A. Bychkov, A. V. Kolesnikov

L. Q. Lai, Zhao 照 Li 李, Yabin Yu +1 more

Abstract At low temperature and under weak magnetic field, non-interacting Fermi gases reveal both Pauli paramagnetism and Landau diamagnetism, and the magnitude of the diamagnetic susceptibility is 1/3 of that of the paramagnetic one. When the temperature is finite and the magnetic field is also finite, we demonstrate that the paramagnetism and diamagnetism start to deviate from the ratio 1/3. For understanding the magnetic properties of an ideal Fermi gas at quite low temperature and under quite weak magnetic field, we work out explicitly the third-order magnetic susceptibility in three cases, from intrinsic spin, orbital motion and in total. An interesting property is in third-order magnetic susceptibilities: when viewing individually, they are both diamagnetic, but in total it is paramagnetic.

Wen Wen, Hui‐jun Li, Bingyan Chen

We study the evolution of the interference patterns of strongly interacting Fermi gases in a harmonic trap after removal of the optical lattice, by numerically solving the superfluid order-parameter equation. We find that for the strongly interacting Fermi gas elastic collisions during the expansion blur the interference peaks. In order to obtain a nearly ballistic expansion, the fast magnetic field ramp technique is applied in experiment. We simulate the fast magnetic field ramp process before expansions of strongly interacting Fermi gases. We find that clear interference patterns are formed, and oscillate for a long time in the harmonic trap. We also calculate the interference patterns in different superfluid regimes, which accord with the experimental observations.

A. Levent Subaşı, Nader Ghazanfari

Atoms with different internal states can exhibit different responses to an artificial magnetic field. An atomic gas mixture of two different components can therefore be interpreted as a mixture of two atomic gases carrying different synthetic charges. We consider the superfluid state of such unequally charged Fermi gases coupled to a magnetic field via the orbital effect and trapped in a torus geometry. The orbital coupling to the magnetic field favors an inhomogeneous superfluid state with optimum finite-center-of-mass-momentum pairing. The resulting population-balanced orbital Fulde-Ferrell (FF) state is robust against the magnetic field and does not undergo pair breaking, unlike the conventional BCS and Fulde-Ferrell-Larkin-Ovchinnikov-type pairing states under the Zeeman effect. We contrast the homogeneous and inhomogeneous cases, emphasizing the advantages of the unequally charged systems, and present their momentum distributions. We conclude that an unequally charged atomic Fermi gas system orbitally coupled to an artificial magnetic field provides an ideal candidate for experimental realization of the FF state.