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Acta Physica Sinica

Impurity problem of alkaline-earth-like atoms near an orbital Feshbach resonance

Yue-Ran Shi, Zhuocheng Lu, Jingkun Wang, Wei Zhang

Published Jan 1, 2019• 3 citations
Publisher

Abstract

In recent years, alkaline-earth and alkaline-earth-like atoms have attracted much research interest in the field of ultracold atom. Especially, the recently discovered orbital Feshbach resonance makes it possible to investigate a strongly interacting gas of alkaline-earth or alkaline-earth-like atoms, which has greatly enriched the scope of quantum simulation in these systems. This paper focuses on the impurity problem in a Fermi gas of 173Yb atoms near orbital Feshbach resonance. In this problem, the impurity atom in 3P0 state will interact with the background Fermi sea in the ground state and the molecule or polaron state will be produced out of the Fermi sea. By using the Chevy-like ansatz, we investigate the properties of the molecule and attractive polaron states firstly and a transition between these two states will be found. Then, some properties of the repulsive polaron state will be introduced, such as the effective mass and the decay rate. Furthermore, the effect of an additional Fermi sea will be considered in this system. Finally, we will discuss the impurity problem in a two-dimensional system.

DOI
10.7498/aps.68.20181937

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In recent years, alkaline-earth and alkaline-earth-like atoms have attracted much research interest in the field of ultracold atom. Especially, the recently discovered orbital Feshbach resonance makes it possible to investigate a strongly interacting gas of alkaline-earth or alkaline-earth-like atoms, which has greatly enriched the scope of quantum simulation in these systems. This paper focuses on the impurity problem in a Fermi gas of 173Yb atoms near orbital Feshbach resonance. In this problem, the impurity atom in 3P0 state will interact with the background Fermi sea in the ground state and the molecule or polaron state will be produced out of the Fermi sea. By using the Chevy-like ansatz, we investigate the properties of the molecule and attractive polaron states firstly and a transition between these two states will be found. Then, some properties of the repulsive polaron state will be introduced, such as the effective mass and the decay rate. Furthermore, the effect of an additional Fermi sea will be considered in this system. Finally, we will discuss the impurity problem in a two-dimensional system.
We study the impurity problem in a Fermi gas of 173 Yb atoms near an orbital Feshbach resonance (OFR), where a single moving particle in the 3 P 0 state interacts with two background Fermi seas of particles in different nuclear states of the ground 1 S 0 manifold. By employing wave function ansatz to molecule and polaron states, we investigate various properties of the molecule, the attractive polaron, and the repulsive polaron states. In comparison to the case where only one Fermi sea is populated, we find that the presence of an additional Fermi sea acts as an energy shift between the two channels of the OFR. In addition, quantum fluctuations near the Fermi level can also induce sizable effects to various properties of the attractive and repulsive polarons.
We study the impurity problem in a Fermi gas of 173^{173}173Yb atoms near an orbital Feshbach resonance, where a single moving particle in the 3P0^3P_03P0​ state interacting with two background Fermi seas of particles in different nuclear states of the ground 1S0^1S_01S0​ manifold. By employing wave function ansatzs for molecule and polaron states, we investigate various properties of the molecule, the attractive polaron, and the repulsive polaron states. We find that in comparison to the case of only one Fermi sea is populated, the presence of an additional Fermi sea acts as an energy shift between the two channels of the orbital Feshbach resonance. Besides, the fluctuation around the Fermi level would also bring sizable effects to the attractive and repulsive polaron states.
We characterize properties of the so-called repulsive polaron across the recently discovered orbital Feshbach resonance in alkaline-earth-metal-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 lifetime of the repulsive polaron is nonmonotonic in the Zeeman-field detuning between 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.
We study the impurity problem in a gas of 173Yb^{173}\mathrm{Yb}173Yb atoms near the recently discovered orbital Feshbach resonance. In an orbital Feshbach resonance, atoms in the electronic ground state 1S0^{1}S_{0}1S0​ interact with those in the long-lived excited 3P0^{3}P_{0}3P0​ state with magnetically tunable interactions. We consider an impurity atom with a given hyperfine spin in the 3P0^{3}P_{0}3P0​ state interacting with a single-component Fermi sea of atoms in the ground 1S0^{1}S_{0}1S0​ manifold. Close to the orbital Feshbach resonance, the impurity can induce collective particle-hole excitations out of the Fermi sea, which can be regarded as the polaron state. As the magnetic field decreases, a molecular state becomes the ground state of the system. We show that a polaron to molecule transition exists in 173Yb^{173}\mathrm{Yb}173Yb atoms close to the orbital Feshbach resonance. Furthermore, due to the spin-exchange nature of the orbital Feshbach resonance, the formation of both the polaron and the molecule involve spin-flipping processes with interesting density distributions among the relevant hyperfine spin states. We show that the polaron to molecule transition can be detected using Raman spectroscopy.
We propose to realize a strongly interacting Fermi superfluid near a narrow Feshbach resonance using the recently discovered ``orbital Feshbach resonance.'' The orbital Feshbach resonance is a type of magnetic field tunable scattering resonance theoretically predicted and experimentally observed recently in the alkaline-earth-metal-like 173Yb^{173}\mathrm{Yb}173Yb atom. We first show that the orbital Feshbach resonance is a narrow resonance in energy, while it is hundreds Gauss wide in terms of magnetic field strength, taking the advantage that the magnetic moment difference between the open and closed channels is quite small. Therefore, this is an ideal platform for the experimental realization of a strongly interacting Fermi superfluid with narrow resonance. We further show that the transition temperature for the Fermi superfluid in this system, especially at the BCS side of the resonance, is even higher than that in a wide resonance, which is also due to the narrow character of this resonance. Our results will encourage experimental efforts to realize Fermi superfluid in the alikaline-earth-metal-like 173Yb^{173}\mathrm{Yb}173Yb system, the properties of which will be complementary to extensively studied Fermi superfluids nearby a wide resonance in alkali-metal 40K^{40}\mathrm{K}40K and 6Li^{6}\mathrm{Li}6Li systems.
We consider an impurity problem in a quasi-two-dimensional Fermi gas, where a spin-down impurity is immersed in a Fermi sea of N spin-up atoms. Using a variational approach and an effective two-channel model, we obtain the energy for a wide range of interaction strength and for various different mass ratios between the impurity and the background fermion in the context of heteronuclear mixture. We demonstrate that in a quasi-two-dimensional Fermi gas there exists a transition of the ground state from polaron in the weakly interacting region to molecule in the strongly interacting region. The critical interaction strength of the polaron–molecule transition is non-universal and depends on the particle density of the background Fermi sea. We also investigate the excited repulsive polaron state, and find similar non-universal behavior.