The body-centered cubic A15-structured cesium fulleride Cs ₃ C ₆₀ is not superconducting at ambient pressure and is free from disorder, unlike the well-studied face-centered cubic A ₃ C ₆₀ alkali metal fulleride superconductors. We found that in Cs ₃ C ₆₀ , where the molecular valences are precisely assigned, the superconducting state at 38 kelvin emerges directly from a localized electron antiferromagnetic insulating state with the application of pressure. This transition maintains the threefold degeneracy of the active orbitals in both competing electronic states; it is thus a purely electronic transition to a superconducting state, with a dependence of the transition temperature on pressure-induced changes of anion packing density that is not explicable by Bardeen-Cooper-Schrieffer (BCS) theory.

Understanding the relationship between the superconducting, the neighboring insulating, and the normal metallic state above T_c is a major challenge for all unconventional superconductors. The molecular A₃C₆₀ fulleride superconductors have a parent antiferromagnetic insulator in common with the atom-based cuprates, but here, the C₆₀^3– electronic structure controls the geometry and spin state of the structural building unit via the on-molecule Jahn-Teller effect. We identify the Jahn-Teller metal as a fluctuating microscopically heterogeneous coexistence of both localized Jahn-Teller–active and itinerant electrons that connects the insulating and superconducting states of fullerides. The balance between these molecular and extended lattice features of the electrons at the Fermi level gives a dome-shaped variation of T_c with interfulleride separation, demonstrating molecular electronic structure control of superconductivity.

We present a detailed study of ${}^{75}\text{A}\text{s}$ nuclear magnetic resonance Knight shift and spin-lattice relaxation rate in the normal state of stoichiometric polycrystalline LiFeAs. Our analysis of the Korringa relation suggests that LiFeAs exhibits strong antiferromagnetic fluctuations, if transferred hyperfine coupling is a dominant interaction between ${}^{75}\text{A}\text{s}$ nuclei and Fe electronic spins, whereas for an on-site hyperfine coupling scenario, these are weaker, but still present to account for our experimental observations. Density-functional calculations of electric field gradient correctly reproduce the experimental values for both ${}^{75}\text{A}\text{s}$ and ${}^7\text{L}\text{i}$ sites.

A study of bright matter-wave solitons of a cesium Bose-Einstein condensate (BEC) is presented. Production of a single soliton is demonstrated and dependence of soliton atom number on the interatomic interaction is investigated. Formation of soliton trains in the quasi-one-dimensional confinement is shown. Additionally, fragmentation of a BEC has been observed outside confinement, in free space. In the end a double BEC production setup for studying soliton collisions is described.

The structural, electronic, and magnetic properties of the superconducting ${\text{NdFeAsO}}_{1-x}{\text{F}}_x$ phases ($T_C=43\text{K}$ for $x=0.15$) have been investigated experimentally by high-resolution synchrotron x-ray powder diffraction, magnetization and ${}^{75}\text{A}\text{s}$ NMR measurements. Density-functional calculations were performed to calculate and analyze the electric field gradient and the density of states. Compared to LaFeAsO family, the NdFeAsO family shows a contraction of the lattice parameters with shorter rare-earth (RE)-As bond distances, an increased thickness of the ${\text{As-Fe}}_2\text{-As}$ layer, and less distorted ${\text{Fe-As}}_4$ tetrahedra. The ${}^{75}\text{A}\text{s}$ quadrupole frequencies are enhanced with respect to the La analogs. This is due to a more prolate $\text{As}4p$ electron distribution mainly caused by the reduced lattice parameters and not by the presence of $\text{Nd}4f$ electrons. A non-negligible hyperfine coupling between the ${}^{75}\text{A}\text{s}$ nuclei and the $\text{Nd}4f$ states indicates a weak coupling between the REO and FeAs layer and possibly opens the channel for a Ruderman-Kittel-Kasuya-Yosida (RKKY)-type interaction between localized $\text{Nd}4f$ moments mediated by itinerant $\text{Fe}3d$ and/or $\text{Nd}5d$ states.