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.

Alkali-earth atoms have a long-lived electronic excited state, and when atoms in this excited state are localized in the Fermi sea of ground state atoms by an external potential, they serve as magnetic impurities, due to the spin-exchange interaction between the excited and the ground state atoms. This can give rise to the Kondo effect. However, in order to achieve this effect in current atomic gas experiment, it requires the Kondo temperature to be increased to a sizable portion of the Fermi temperature. In this paper we calculate the confinement-induced resonance (CIR) for spin-exchanging interaction between the ground and the excited states of the alkali-earth atoms, and we propose that the spin-exchange interaction can be strongly enhanced by utilizing the CIR. We analyze this system by the renormalization group approach, and we show that nearby a CIR, the Kondo temperature can be significantly enhanced. * Electronic address: pengzhang@ruc.edu.cn † Electronic address: hzhai@tsinghua.edu.cn arXiv:1509.01350v3 [cond-mat.quant-gas]

In this letter we show that the recently theoretically predicted and experimentally observed "orbital Feshbach resonance" in alkali-earth-like 173 Yb atom is a narrow resonance in energy, while it is hundreds Gauss wide in term 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 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 alkali-earth-like 173 Yb system, the properties of which will be complementary to extensively studied Fermi superfluids nearby a wide resonance in alkali 40 K and 6 Li systems.Pairing of fermions is a universal mechanism for both superconductivity in materials and Fermi superfluid in neutral atoms. In the weakly attractive BCS regime, the transition temperature T c is much smaller than the Fermi temperature T F [1]. In cold atom systems, the Feshbach resonance (FR) provides a tool to significantly enhance the attraction between atoms [2, 3], with which the T c can be increased to the order of 0.1T F [4, 5]. So far, in term of T c /T F , this is the highest transition temperature ever achieved and in the past decade or so it has been realized and extensively studied by many laboratories with 40 K and 6 Li atoms [4, 5].Interactions between ultracold atomic gases are usually dominated by s-wave scattering and can be well described by the s-wave phase shift θ k , which can be expanded as [2][3][4] where k is the relative momentum between two atoms. The leading order term gives the scattering length a s which diverges at a resonance. The next order term is characterized by an effective range r 0 , which describes how fast the scattering phase shift changes in energy. Effective range also controls how sensitive the a s depends on the magnetic field strength. Normally around a FR the magnetic field dependence of a s can be casted intowhere B res is the field location of a FR, a bg is so-called the background scattering length, ∆ B is the resonance width. Neglecting the short range van de Waals physics, ∆ B is related to r 0 via [6,7] where m is the single-atom mass and δµ is the magnetic moment difference between the open and closed channels. A resonance can be classified as a wide or narrow resonance, depending on how r 0 compares with the characteristic length scales of the system. This length scale could be either van der Waals length r vdW or the inverse of the Fermi momentum 1/k F . One can introduce a parameter called s res = 8πr vdW /(Γ(1/4) 2 |r 0 |), and resonances with s res 1 are called narrow resonances [3]. So far all experiments on fermion superfluid nearby a FR are performed with a wide resonance, such ...

The Kondo effect describes the spin-exchanging interaction between localized impurity and the itinerant fermions. The ultracold alkaline-earth atomic gas provides a natural platform for quantum simulation of the Kondo model, utilizing its long-lived clock state and the nuclear-spin exchanging interaction between the clock state and the ground state. One of the key issue now is whether the Kondo temperature can be high enough to be reached in current experiment, for which we have proposed using a transverse confinement to confine atoms into a one-dimensional tube and to utilize the confinement-induced resonance to enhance the Kondo coupling. In this work, we further consider the 1 + 0 dimensional scattering problem when the clock state is further confined by an axial harmonic confinement. We show that this axial confinement for the clock state atoms not only plays a role for localizing them, but also can act as an additional control knob to reach the confinement-induced resonance. We show that by combining both the transverse and the axial confinements, the confinement-induced resonance can be reached in the practical conditions and the Kondo effect can be attainable in this system. I. MOTIVATION AND BACKGROUNDIn the past decades, experiments in cold atom systems have successfully explored many intriguing quantum many-body phenomena of different paradigms, including fermion pairing and the BCS-BEC crossover, the Bose and the Fermi Hubbard models [1], the KosterlizeThouless transition [1], one-dimensional integrable models [2], spin-orbit coupling [3] and topological models [4]. Exploring these phenomena with cold atom systems have a list of advantages, for instance, one can access physical quantities that have not been measured before in their condensed matter realizations, and one can also study non-equilibrium dynamics in a highly controllable way. However, until now there is still one important category that has not been experimentally realized with cold atom systems yet, despite of quite a few existing proposals [5][6][7][8][9][10][11][12][13][14], and that is the Kondo physics.The Kondo model describes the spin-exchanging interaction between localized impurities and the itinerant fermions [15]. The alkaline-earth atomic gases have natural advantages for performing quantum simulation of the Kondo model. The schematic energy level of single alkaline-earth atoms is shown in Fig. 1. First of all, there is a long-lived electronic excited state known as the clock state, usually denoted by |e . Atoms in this clock state generically has a different ac polarization comparing to atoms in their electronic ground state, usually denoted by |g , except for lasers with a magic wavelength [16,17]. Therefore, it is easy to realize a situation that lasers cre- * Electronic address: rine.zhang@gmail.com † Electronic address: pengzhang@ruc.edu.cn |e, "i |e, #i |g, #i |g, "i ate a deep lattice for |e -atoms and make them localized as impurities, while |g -atoms experience a quite shallow lattice and remain itinerant, as shown in...

We herein report on the density-and temperature-dependent decay of the 93m Nb nuclear excited atom and present a simple interpretation of the underlying physics. This anomaly indicates nuclear resonant absorption and delocalisation of the long-lived Mössbauer state in the crystal. A non-linear magnetoelectric response, on low-frequency drive current, appeared in the bulk metal of a high-purity niobium crystal and then disappeared along with the disappearance of delocalised nuclear excitation. Several non-linear resonant peaks, of the order of several hundred Hertz, increased in magnitude with the applied magnetic field, and the central frequencies of these peaks decreased with temperature.