Lone Pair Effect, Structural Distortions and Potential for Superconductivity in Tl Perovskites

Drawing the analogy to BaBiO3, we investigate via ab-initio electronic structure calculations potential new superconductors of the type ATlX3 with A = Rb, Cs and X = F, Cl, and Br, with a particular emphasis on RbTlCl3. Based on chemical reasoning, supported by the calculations, we show that Tl-based perovskites have structural and charge instabilities driven by the lone pair effect, similar to the case of BaBiO3, effectively becoming A2Tl1+Tl3+X6. We find that upon hole doping of RbTlCl3, structures without Tl1+, Tl3+ charge disproportionation become more stable, although the ideal cubic perovskite, often viewed as the best host for superconductivity, should not be the most stable phase in the system. The known superconductor (Sr,K)BiO3 and hole doped RbTlCl3, predicted to be most stable in the same tetragonal structure, display highly analogous calculated electronic band structures.Comment: 5 pages, 5 figure

Ir d-band Derived Superconductivity in the Lanthanum-Iridium System LaIr3

The electronic properties of the heavy metal superconductor LaIr3 are reported. The estimated superconducting parameters obtained from physical properties measurements indicate that LaIr3 is a BCS-type superconductor. Electronic band structure calculations show that Ir d- states dominate the Fermi level. A comparison of electronic band structures of LaIr3 and LaRh3 shows that the Ir-compound has a strong spin-orbit-coupling effect, which creates a complex Fermi surface.Comment: 6 pages and 5 figure

Strong and fragile topological Dirac semimetals with higher-order Fermi arcs

Dirac and Weyl semimetals both exhibit arc-like surface states. However, whereas the surface Fermi arcs in Weyl semimetals are topological consequences of the Weyl points themselves, the surface Fermi arcs in Dirac semimetals are not directly related to the bulk Dirac points, raising the question of whether there exists a topological bulk-boundary correspondence for Dirac semimetals. In this work, we discover that strong and fragile topological Dirac semimetals exhibit one-dimensional (1D) higher-order hinge Fermi arcs (HOFAs) as universal, direct consequences of their bulk 3D Dirac points. To predict HOFAs coexisting with topological surface states in solid-state Dirac semimetals, we introduce and layer a spinful model of an s–d-hybridized quadrupole insulator (QI). We develop a rigorous nested Jackiw–Rebbi formulation of QIs and HOFA states. Employing ab initio calculations, we demonstrate HOFAs in both the room- (α) and intermediate-temperature (α″) phases of Cd3As2, KMgBi, and rutile-structure (β′-) PtO2