Jan Bała

Spin-orbital physics in the optical conductivity of quarter-filled manganites

Using finite-temperature diagonalization we investigate the optical conductivity

Spin excitations in ferromagnetic manganites with orbital order

\ensuremath{\sigma}(\ensuremath{\omega})

Quasiparticles in Photoemission Spectra of Manganites

and spin-orbital dynamics in the CE phase of half-doped manganites. We find

Orbital polarons in LaMnO3

\ensuremath{\sigma}(\ensuremath{\omega})

Quasiparticles in doped CuO2 and Cu3O4 planes

characterized by a broad spectrum with pronounced optical gap due to charge ordering induced by Coulomb and further-neighbor Jahn-Teller interactions. With increasing temperature the conductivity shows a significant change over a wide energy range with a characteristic shift towards lower frequencies. In the low-temperature CE phase we observe in-gap absorption due to combined orbiton-spin excitations.

Spin polarons in the t-t'-j model

The ferromagnetic metallic phase of doped cubic manganites with orbital order is investigated in a two-band double exchange model extended by Jahn–Teller (JT) terms. Evaluating the spin wave self-energy in the lowest order 1/S expansion, one finds that spin excitations are anisotropic and depend on the type of occupied eg orbitals. In the case of a small splitting between eg orbital energies, magnon dispersion exhibits a pronounced asymmetry between low and high hole doping, while a strong JT effect leads to the alternating orbital order which can reduce the spin stiffness by one order of magnitude. For a bilayer system, the kinetic energy induces an x2 − y2 orbital character and is responsible for a drastic change in the interplane exchange coupling in the doping range 0.3 < x < 0.5.

Zhang-Rice localization and quasiparticles in CuO2 planes

We compare the spectral functions of a hole moving in the orbital-ordered undoped LaMnO3, obtained using a self-consistent Born approximation. The quasiparticle (QP) dispersion and spectral weight depend critically on the type of orbital ordering. If a hole scatters on orbital excitations, the QP dispersion on the orbiton energy scale is modified by orbital polarization and by electron-lattice coupling. A lower QP dispersion and quantum decoherence are obtained due to the inter-planar hole-magnon scattering in the A-AF phase which disproves the classical concept of a ferromagnetic polaron.

Zhang-rice localization, quasi-particle dispersions, and the photoemission of nio

Abstract We investigate the spectral functions and orbital correlation functions relative to the position of an eg hole moving in the ferromagnetic plane of orbitally ordered LaMnO3. Polarization of orbitals around the hole leads to a very narrow quasiparticle band and to a confinement of the hole in an orbital polaron with the shape strongly depending on the type of the orbital order.

Quantum decoherence in the spectral functions of undoped LaMnO3

Abstract Using the spin-fermion multiband models derived for the valence electrons in CuO 2 and Cu 3 O 4 planes we have found the sector of Zhang–Rice states coexisting with higher energy oxygen states. The dispersions of weak states and higher energy band-like features are even in quantitative agreement with the experimental data.

Quasiparticles and the structure of orbital polarons in ferromagnetic LaMnO3

Abstract We investigate the effect of the next-nearest neighbour hopping terms t ′ and the three-site hopping terms in the t - t ′- J model. We derive a more realistic hole-magnon vertex which leads to vanishing of the quasiparticles in some parts of the Brillouin zone even for relatively small t′ ⋍ 0.2 t , while quasiparticles survive for t ′