Giniyat Khaliullin

Kitaev-Heisenberg model on a honeycomb lattice: possible exotic phases in iridium oxides A2IrO3.

We derive and study a spin one-half Hamiltonian on a honeycomb lattice describing the exchange interactions between Ir4+ ions in a family of layered iridates A2IrO3 (A=Li,Na). Depending on the microscopic parameters, the Hamiltonian interpolates between the Heisenberg and exactly solvable Kitaev models. Exact diagonalization and a complementary spin-wave analysis reveal the presence of an extended spin-liquid phase near the Kitaev limit and a conventional Néel state close to the Heisenberg limit. The two phases are separated by an unusual stripy antiferromagnetic state, which is the exact ground state of the model at the midpoint between two limits.

Intense paramagnon excitations in a large family of high-temperature superconductors

In the copper oxide superconductors, spin fluctuations might be involved in the electronic pairing mechanism. The case for such magnetically mediated superconductivity is now strengthened by the discovery of high-energy magnetic excitations that are not affected by chemical doping levels within several cuprates.

Charge and orbital order in half-doped manganites

Manganese oxides with the general composition R12xAxMnO3 (where R and A are rare- and alkaline-earth ions, respectively) have attracted considerable attention because of their unusual magnetic and electronic properties. In some of these materials, metal-insulator transitions can be observed where both conductivity and magnetization change markedly. The x 0 and x 1 end members of the R12xAxMnO3 family are insulating and antiferromagnetic (AF) with the Mn ion in the Mn 31 and Mn 41 state, respectively. For intermediate x, the average Mn valence is noninteger and the material is generally metallic or semiconducting. Most of the perovskite manganites show a ferromagnetic (FM) ground state when the holes are optimally doped (usually 0.2 , x , 0.5) and anisotropic antiferromagnetic (AFM) phases for x . 0.5. The half-doped manganites, with x 1 , are very particular. Magnetically these systems form FM

Magnetic excitation spectra of Sr2IrO4 probed by resonant inelastic x-ray scattering: establishing links to cuprate superconductors.

Jungho Kim, D. Casa, M. H. Upton, T. Gog, Young-June Kim, J. F. Mitchell, M. van Veenendaal, M. Daghofer, J. van den Brink, G. Khaliullin, B. J. Kim Advanced Photon Source, Argonne National Laboratory, Argonne, Illinois 60439, USA Department of Physics, University of Toronto, Toronto, Ontario, Canada M5S 1A7 Material Science Division, Argonne National Laboratory, Argonne, IL 60439, USA Department of Physics, Northern Illinois University, De Kalb, IL 60115, USA Institute for Theoretical Solid Sate Physics, IFW Dresden, Helmholtzstr. 20, 01069 Dresden, Germany and Max Planck Institute for Solid State Research, Heisenbergstrae 1, D-70569 Stuttgart, Germany (Dated: December 11, 2012)

Zigzag magnetic order in the iridium oxide Na2IrO3.

We explore the phase diagram of spin-orbit Mott insulators on a honeycomb lattice, within the Kitaev-Heisenberg model extended to its full parameter space. Zigzag-type magnetic order is found to occupy a large part of the phase diagram of the model, and its physical origin is explained as due to interorbital t2g − eg hopping. Magnetic susceptibility and spin wave spectra are calculated and compared to the experimental data, obtaining thereby the spin coupling constants in Na2IrO3 and Li2IrO3.

Orbital liquid in three-dimensional mott insulator: LaTiO3

We present a theory of spin and orbital states in Mott insulator

Spin-controlled Mott-Hubbard bands in LaMnO3 probed by optical ellipsometry

LaTiO_3

Orbital order and fluctuations in mott insulators

. The spin-orbital superexchange interaction between

Spin Order due to Orbital Fluctuations: Cubic Vanadates

d^1(t_{2g})

Fingerprints of spin-orbital physics in cubic Mott insulators: Magnetic exchange interactions and optical spectral weights

ions in cubic crystal suffers from a pathological degeneracy of orbital states at classical level. Quantum effects remove this degeneracy and result in the formation of the coherent ground state, in which the orbital moment of