ABSTRACT
It is a fundamental truth in solid compounds that the physical properties follow the symmetry of the crystal structure. Nowhere is the effect of symmetry more pronounced than in the electronic and magnetic properties of materials-even the projection of the bulk crystal symmetry onto different crystal faces is known to have a substantial impact on the surface electronic states. The effect of bulk crystal symmetry on the properties of superconductors is widely appreciated, although its study presents substantial challenges. The effect of a lack of a center of symmetry in a crystal structure, for example, has long been understood to necessitate that the wave function of the collective electron state that gives rise to superconductivity has to be more complex than usual. However, few nonhypothetical materials, if any, have actually been proven to display exotic superconducting properties as a result. We introduce two new superconductors that in addition to having noncentrosymmetric crystal structures also have chiral crystal structures. Because the wave function of electrons in solids is particularly sensitive to the host material's symmetry, crystal structure chirality is expected to have a substantial effect on their superconducting wave functions. Our two experimentally obtained chiral noncentrosymmetric superconducting materials have transition temperatures to superconductivity that are easily experimentally accessible, and our basic property characterization suggests that their superconducting properties may be unusual. We propose that their study may allow for a more in-depth understanding of how chirality influences the properties of superconductors and devices that incorporate them.
ABSTRACT
Previously unreported σ-phases in the ternary niobium-based systems Nb-X-Ga for X = Ru, Rh, Pd, Ir, Pt, Au, and Nb-X-Al for X = Ir, and Pt are presented, prepared by arc-melting followed by annealing at 1000 °C for 1 week. The phases are primitive tetragonal (P42/mnm, no. 136) with lattice parameters of a = 9.8336(2)-9.9432(1) Å and c = 5.1098(1)-5.1718(1) Å. Refinements of the single crystal X-ray diffraction data for the Ru and Ir containing materials gave the formulas Nb20Ru5Ga5 and Nb20Ir4Ga6, showing mixing of X/Ga on the crystallographic 8i2 and 2a sites of the structure, a type of disorder frequently found in σ-phases. We present a graphical classification for ternary σ-phases that places our materials in context with previous materials. The materials do not show evidence of bulk superconductivity above 2 K. Synthesis of equivalent Ta-based σ-phases was attempted but they were not found.
