Electrons in solids are in motion within the energy band reflecting the lattice structure of each material. The Coulomb interaction, electron-lattice interaction, and spin-orbit interaction have nontrivial effects on the motion of electrons and induce various interesting phenomena. Our aim is to elucidate the emergent quantum phenomena induced by cooperation or competition of these interactions, using state-of-the-art computational methods for condensed matter physics. Our current focus is on various functional transition metal oxides, topological materials, and heterostructures made of these materials. Our research will lead not only to clarify the mechanism of quantum phenomena in existent materials but also to propose novel materials.
Mechanism of novel insulating state and possible superconductivity induced by a spin-orbit coupling
Electrons in solids are moving around, affected by the Coulomb interaction, electron-lattice interaction, and spin-orbit interaction, which induces different behaviors characteristic of each material. Recently, the study for the spin-orbit coupling has greatly progressed and attracted much attention. In the 5d transition metal oxide Sr2IrO4, the spin and orbital degrees of freedom are strongly entangled due to the large spin-orbit coupling and the novel quantum state is formed. Sr2IrO4 is also expected to be a possible superconducting material with a great deal of similarities to the parent compound of cuprate high-temperature superconductivity
We have studied the detailed electronic properties of a 3-orbital Hubbard model for Sr2IrO4 with several computational methods. Our calculations have clearly shown that the ground state of this material is an effective total angular momentum Jeff=1/2 antiferromagnetic insulator, where J eff is “pseudospin”,formed by spin and orbital degrees of freedom due to the strong spin-orbit coupling (x-AFI in Fig. (a)). We have also proposed that the dx2-y2-wave “pseudospin singlet” superconductivity (SC in Fig. (b)) is induced by electron doping into the Jeff=1/2 antiferromagnetic insulator Sr2IrO4.
Ground state phase diagram of 3-orbital Hubbard model with a spin-orbit coupling. (a) Electron density n=5, (b) n>5.
Two-dimensional materials and interfaces can convert spin current into a vortex of charge current
