We report on the experimental realization of ultracold 174 Yb-7 Li (Boson-Boson) and 173 Yb-7 Li (Fermion-Boson) mixtures. They are loaded into three dimensional (3D) or one dimensional (1D) optical lattices that are species-selectively deep for the heavy Ytterbium (Yb) and shallow for the light bosonic Lithium (Li) component, realizing novel mixed dimensional systems. In the 1D optical lattice the band structure of 173 Yb is reconstructed in the presence of 7 Li. Spectroscopic measurements of the 174 Yb-7 Li mixture in the 3D lattice give access to the 174 Yb Mott-insulator structure. Ground state inter-species scattering lengths are determined to be |a bg ( 174 Yb-7 Li)| = (1.11 ± 0.17) nm and |a bg ( 173 Yb-7 Li)| = (1.16 ± 0.18) nm. The formation and characterization of an ultracold 173 Yb-7 Li mixture is a first step towards a possible realization of a topological px + i py superfluid in this system.

We found superconductivity in CaSb2 with the transition temperature of 1.7 K by means of electrical-resistivity, magnetic-susceptibility, and specific-heat measurements. This material crystallizes in a nonsymmorphic structure and is predicted to have multiple Dirac nodal lines in the bulk electronic band structure protected by symmetry even in the presence of spin-orbit coupling. We discuss a possible topological superconductivity for the quasi-2-dimensional band originating mainly from one of the antimony sites.

We report the temperature variation of the 119 Sn-Mössbauer spectra of the antiperovskite (inverse perovskite) oxide superconductor Sr3-x SnO. Both superconductive (Sr-deficient) and nonsuperconductive (nearly stoichiometric) samples exhibit major γ-ray absorption with isomer shift similar to that of Mg2Sn. This fact shows that Sr3-x SnO contains the metallic anion Sn 4 -, which is rare especially among oxides. In both samples, we observed another γ-ray absorption with a larger isomer shift, indicating that there is another ionic state of Sn with a higher oxidation number. The temperature dependence of the absorption intensities reveals that the Sn ions exhibiting larger isomer shifts have a lower energy of the local vibration. The larger isomer shift and lower vibration energy are consistent with the values estimated from the first-principles calculations for hypothetical structures with various Sr-deficiency arrangements. Therefore, we conclude that the additional γ-ray absorptions originate from the Sn atoms neighboring the Sr deficiency. :1911.12934v1 [cond-mat.mtrl-sci] arXiv

We report a μSR study on the antiperovskite oxide superconductor Sr 3−x SnO. By using transverse-field μSR, we observed an increase of the muon relaxation rate upon cooling below the superconducting transition temperature T c = 5.4 K, evidencing bulk superconductivity. The exponential temperature dependence of the relaxation rate σ at low temperatures suggests a fully gapped superconducting state. We evaluated the zerotemperature penetration depth λ(0) ∝ 1/ √ σ (0) to be around 320-1020 nm. Such a large value is consistent with the picture of a doped Dirac semimetal. Moreover, we established that the ratio T c /λ(0) −2 is larger than those of ordinary superconductors and is comparable to those of unconventional superconductors. The relatively high T c for small carrier density may hint at an unconventional pairing mechanism beyond the ordinary phonon-mediated pairing. In addition, zero-field μSR did not provide evidence of broken time-reversal symmetry in the superconducting state. These features are consistent with the theoretically proposed topological superconducting state in Sr 3−x SnO, as well as with ordinary s-wave superconductivity.