Strong coupling theory of spin and orbital excitations in Sr2IrO4

Abstract

We study the low-lying excitations in 5d transition-metal oxide Sr_2IrO_4 on the localized electron picture. We find that Hund's coupling together with the spin-orbit interaction leads to exchange anisotropy which causes the spin wave gap. Introducing the isospin operators acting on Kramers' doublet in Ir atoms, we derive the effective spin Hamiltonian from a multi-orbital Hubbard model with the t_{2g} orbitals in the square lattice. We introduce the Green's functions including the anomalous type for the boson operators by expanding the spin operators in terms of boson operators in the lowest order of 1/S, and solve the coupled equations of motion for those functions. Two modes are found to emerge with slightly different energies, in contrast to the spin waves in the isotropic Heisenberg model. At the $\Gamma$-point, one mode has the zero excitation energy while another has a finite energy. They have the same excitation energy at the M point, but still have different energies at the X point.

6 pages, 2 figures, Latex; Figures are replaced by the revised ones. A few expressions in Secs.II and III are refined

References in corpus (8)

• Mott Insulators in the Strong Spin-Orbit Coupling Limit: From Heisenberg to a Quantum Compass and Kitaev Models
• Novel Jeff = 1/2 Mott State Induced by Relativistic Spin-Orbit Coupling in Sr2IrO4
• Isospin Dynamics in Sr2IrO4 : Forging Links to Cuprate Superconductivity
• Twisted Hubbard Model for Sr2IrO4: Magnetism and Possible High Temperature Superconductivity
• Microscopic study of spin-orbit-induced Mott insulator in Ir oxides
• Two-dimensional Heisenberg behavior of Jeff = 1/2 isospins in the paramagnetic state of spin-orbital Mott insulator Sr2IrO4
• Electronic structures of layered perovskite Sr2MO4 (M=Ru, Rh, and Ir)
• Magnetic couplings, optical spectra, and spin-orbit exciton in 5d electron Mott insulator Sr2IrO4

Cited by in corpus (10)

• Isotropic and Anisotropic Regimes of the Field-Dependent Spin Dynamics in Sr2IrO4: Raman Scattering Studies
• Anisotropic exchange and spin-wave damping in pure and electron-doped Sr${}_2$IrO${}_4$
• Validity and limitations of the superexchange model for the magnetic properties of Sr2IrO4 and Ba2IrO4 mediated by the strong spin-orbit coupling
• Analysis of resonant inelastic x-ray scattering from Sr${}_2$IrO${}_4$ in an itinerant-electron approach
• Magnetic excitation in resonant inelastic x-ray scattering of Sr${}_2$IrO${}_4$: A localized spin picture
• Interplay between Hund's coupling and spin-orbit interaction on elementary excitations in Sr2IrO4
• Collective excitations in Na${}_2$IrO${}_3$
• Possible superconductivity induced by a large spin-orbit coupling in carrier doped iridium oxide insulators: A weak coupling approach
• Pseudo-spin rotation symmetry breaking by Coulomb interaction terms in spin-orbit coupled systems
• Effect of broken symmetry on resonant inelastic x-ray scattering from undoped cuprates