156 research outputs found

    Turning a Band Insulator Into an Exotic Superconductor

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    Understanding exotic, non s--wave--like states of Cooper pairs is important and may lead to new superconductors with higher critical temperatures and novel properties. Their existence is known to be possible but has always been thought to be associated with non--traditional mechanisms of superconductivity where electronic correlations play an important role. Here we use a first principles linear response calculation to show that in doped Bi2_{2}Se3_{3} an unconventional p--wave--like state can be favored via a conventional phonon--mediated mechanism, as driven by an unusual, almost singular behavior of the electron--phonon interaction at long wavelengths. This may provide a new platform for our understanding superconductivity phenomena in doped band insulators.Comment: Published versio

    Computational Design of Axion Insulators Based on 5d Spinels Compounds

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    Based on density functional calculation with LDA+U method, we propose that hypothetical Osmium compounds such as CaOs2O4 and SrOs2O4 can be stabilized in the geometrically frustrated spinel crystal structure. They also show some exotic electronic and magnetic properties in a reasonable range of on-site Coulomb correlation U such as ferromagnetism and orbital magnetoelectric effect characteristic to Axion electrodynamics. Other electronic phases including 3D Dirac metal and Mott insulator exist and would make perspective 5d spinels ideal for applications.Comment: 5 pages, 3 figure

    Electronic Structure and Linear Optical Properties of Sr2_{2}CuO2_{2}Cl2_{2} Studied from the First Principles Calculation

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    First-principles calculations with the full-potential linearized augmented plane-wave (FP-LAPW) method have been performed to investigate detailed electronic and linear optical properties of Sr2_{2}CuO2_{2}Cl2_{2}, which is a classical low-dimensional antiferromagnet (AFM) charge transfer ({\it CT}) insulator. Within the local-spin-density approximation (LSDA) plus the on-site Coulomb interaction UU (LADA+UU) added on Cu 3d orbitals, our calculated band gap and spin moments are well consistent with the experimental and other theoretical values. The energy dispersion relation agrees well with the angle resolved photoemission measurements. Its linear optical properties are calculated within the electric-dipole approximation. The absorption spectrum is found to agree well with the experimental result.Comment: 5 pages, 5 figure

    Efficient Topological Materials Discovery Using Symmetry Indicators

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    Although the richness of spatial symmetries has led to a rapidly expanding inventory of possible topological crystalline (TC) phases of electrons, physical realizations have been slow to materialize due to the practical difficulty to ascertaining band topology in realistic calculations. Here, we integrate the recently established theory of symmetry indicators of band topology into first-principle band-structure calculations, and test it on a databases of previously synthesized crystals. The combined algorithm is found to efficiently unearth topological materials and predict topological properties like protected surface states. On applying our algorithm to just 8 out of the 230 space groups, we already discover numerous materials candidates displaying a diversity of topological phenomena, which are simultaneously captured in a single sweep. The list includes recently proposed classes of TC insulators that had no previous materials realization as well as other topological phases, including: (i) a screw-protected 3D TC insulator, \b{eta}-MoTe2, with gapped surfaces except for 1D helical "hinge" states; (ii) a rotation-protected TC insulator BiBr with coexisting surface Dirac cones and hinge states; (iii) non-centrosymmetric Z2 topological insulators undetectable using the well-established parity criterion, AgXO (X=Na,K,Rb); (iv) a Dirac semimetal MgBi2O6; (v) a Dirac nodal-line semimetal AgF2; and (vi) a metal with three-fold degenerate band crossing near the Fermi energy, AuLiMgSn. Our work showcases how the recent theoretical insights on the fundamentals of band structures can aid in the practical goal of discovering new topological materials

    Robust Half-Metallic Character and Large Oxygen Magnetism in a Perovskite Cuprate

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    The new perovskite cuprate material Sr8_{8}CaRe3_{3}Cu4_{4}O24_{24}, which behaves ferrimagnetically and shows an unusually high Curie temperature (Tc∼T_c \sim 440 K), is found from density-functional theory calculation to display several surprising properties after hole doping or chemical substitution: (1) Half metal (HM) is realized by replacing Re with W or Mo while TcT_c remains high; (2) hole-doped Sr8_{8}CaRe3_{3}Cu4_{4}O24_{24} is also HM with high TcT_c. Moreover, we find that the O atoms will carry a large magnetic moment after hole doping, which is in sharp contrast with the generally accepted concept that magnetism in solid requires partially filled shells of dd or ff electrons in cations. The material Sr8_8CaRe3_3Cu4_4O24_{24} is therefore expected to provide a very useful platform for material design and development.Comment: 5 pages and 4 figure
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