Fyzikální ústav Akademie věd ČR

The discovery of quantum spin Hall effect and new states of solids characterized by non-trivial topology in materials with strong spin-orbit coupling lead to a substantial interest in materials with 5d electrons. Combination of the strong spin-orbit coupling, electron-electron interaction and crystal structure gives rise to unique transport, magnetic of thermodynamic properties in some of them. We have studied the temperature dependence of the magnetic order and electrical conductivity of iridium oxide Sr₂IrO₄ and Ba₂IrO₄ in collaboration with colleagues from the University of Tokyo and Oak Ridge National Lab (USA). Using numerical methods developed in the Institute of Physics we have explain the strong temperature dependence of the gap observed experimentally and demonstrated its connection to the anti-ferromagnetic order. Our calculations show how Sr₂IrO₄ evolves gradually from an anti-ferromagnetic insulator to a paramagnetic metal with increasing temperature. These results point out some analogies to cuprate superconductors and provide a starting point for investigation of materials obtained by strontium substitution in search for potential superconductivity. Using numerical methods developed in the Institute of Physics we have explained the relationship between the gap size and the anti-ferromagnetic order in crystals of Sr2IrO4 from the iridates group. These materials are subject of intense investigation due to their unusual magnetic and transport properties.

The electronic spectrum of Sr₂IrO₄ at various temperatures. Gap opening at 580 K is related to establishing of the long-range anti-ferromagnetic order.

¹Department of Applied Physics, University of Tokyo, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
²JST-PRESTO, Kawaguchi, Saitama 332-0012, Japan
³JST-CREST, Hongo, Bunkyo-ku, Tokyo, 113-8656, Japan
⁴Institute of Physics, Academy of Sciences of the Czech Republic, Cukrovarnická 10, Praha 6, 162 53, Czech Republic
⁵Institute for Theoretical Physics, ETH Zurich, CH-8093 Zurich, Switzerland
⁶Department of Physics and Astronomy, The University of Tennessee, Knoxville, Tennessee 37996, USA