Repulsive polarons in alkaline-earth-metal-like atoms across an orbital Feshbach resonance

Abstract

We characterize properties of the so-called repulsive polaron across the recently discovered orbital Feshbach resonance in alkaline-earth(-like) atoms. Being a metastable quasiparticle excitation at the positive energy, the repulsive polaron is induced by the interaction between an impurity atom and a Fermi sea. By analyzing in detail the energy, the polaron residue, the effective mass, and the decay rate of the repulsive polaron, we reveal interesting features that are intimately related to the two-channel nature of the orbital Feshbach resonance. In particular, we find that the life time of the repulsive polaron is non-monotonic in the Zeeman-field detuning bewteen the two channels, and has a maximum on the BEC-side of the resonance. Further, by considering the stability of a mixture of the impurity and the majority atoms against phase separation, we show that the itinerant ferromagnetism may exist near the orbital Feshbach resonance at appropriate densities. Our results can be readily probed experimentally, and have interesting implications for the observation of itinerant ferromagnetism near an orbital Feshbach resonance.

Controlling the interaction of ultracold alkaline-earth atoms

“…In previous studies in condensed matter materials and ultracold alkalinemetal atomic gases, both two types of impurity physics have been studied separately. It is interesting to note that both two types of impurity physics can exist in the system of two orbital mixture of cold 173 Yb gases [42,[85][86][87][88]. By tuning the magnetic field strength from zero to finite, and by tuning the confinement potential, the interaction can be tuned from the spin-exchanging interaction dominated regime to the spin-independent interaction dominated regime; and by tuning the external lattice potential, one can tune the impurity from localized to mobile.…”

“…In AE atoms, there are two ways to realize spin-orbit coupling, either by coupling two nuclear spin state in 1 S 0 manifold via Raman coupling [78][79][80][81] or by directly coupling 1 S 0 and 3 P 0 states by a laser [20,21]. Here we focus on the later because in this setting, there is no intermediate state involved and heating due to spontaneous emission can be avoided, which has been shown in both 88 Sr and 173 Yb atoms [20,21]. Nevertheless, if there is no FR between these two states, topological superfluid is still not possible.…”

Frustrated orbital Feshbach resonances in a Fermi gas

“…Intuitively, this means that atoms can no longer scatter into the closed channel at an arbitrary momentum, but can only do so within a restricted range of momenta which is set by the Fermi sea. We stress that the case we consider is different from the more standard scenario of a spin imbalance in the open channel [59][60][61].…”

Single-particle Excitations and Strong Coupling Effects in the BCS–BEC Crossover Regime of a Rare-Earth Fermi Gas with an Orbital Feshbach Resonance

“…Here, the particle number N α=o,c in the α-channel is calculated from the ATMA single-particle Green's function in Eq. (9) as…”

“…In cold Fermi gas physics, an orbital Feshbach resonance (OFR) has recently attracted much attention as a promising pairing mechanism of a superfluid gas of group 2 (rare earth) Fermi atoms. [1][2][3][4][5][6][7][8][9][10][11] The ordinary broad magnetic Feshbach resonance (MFR), 13) which is the pairing mechanism of superfluid 40 K 14) and 6 Li Fermi gases, [15][16][17] strongly relies on the character of the group 1 (alkali metal) elements that one electron occupies the outermost s-orbital, giving the total electron spin S = 1/2. Thus, MFR does not exist in the group 2 elements, because their ground state always has two electrons in the outermost s-orbital, giving the total electron spin S = 0.…”