Low-energy Mott-Hubbard excitations in LaMnO_3 probed by optical ellipsometry (2009)
Kovaleva, N. N., Oles, Andrzej M., Balbashov, A. M., Maljuk, A., Argyriou, D. N., Khaliullin, G., ...
We present a comprehensive ellipsometric study of an untwinned, nearly stoichiometric LaMnO_3 crystal in the spectral range 1.2-6.0 eV at temperatures 20 K < T < 300 K. The complex dielectric...
Low-energy Mott-Hubbard excitations in LaMnO$_3$ (2009)
Kovaleva, N. N., Oles, Andrzej M., Balbashov, A. M., Maljuk, A., Argyriou, D. N., Khaliullin, G., ...
More discussion from the theory is suggested
Exact solution for a quantum compass ladder (2009)
Brzezicki, Wojciech, Oles, Andrzej M.
We introduce a spin ladder with antiferromagnetic Ising ZZ interactions along the legs, and interactions on the rungs which interpolate between the Ising ladder and the quantum compass ladder. We...
Compass model on a ladder and square clusters (2009)
Brzezicki, Wojciech, Oles, Andrzej M.
We obtained exact heat capacities of the quantum compass model on the square L x L clusters with L=2,3,4,5 using Kernel Polynomial Method and compare them with heat capacity of a large compass...
Spin-wave theory for dimerized ferromagnetic chains (2009)
Herzog, Alexander, Horsch, Peter, Oles, Andrzej M., Sirker, Jesko
We describe a Peierls dimerization which occurs in ferromagnetic spin chains at finite temperature, within the modified spin-wave theory. Usual spin-wave theory is modified by introducing a Lagrange...
Orbitally induced string formation in the spin-orbital polarons (2009)
Wohlfeld, Krzysztof, Oles, Andrzej M., Horsch, Peter
We study the spectral function of a single hole doped into the (a,b) plane of the Mott insulator LaVO$_3$, with antiferromagnetic (AF) spin order of S=1 spins accompanied by alternating orbital (AO)...
Spin--orbital physics in transition metal oxides (2009)
We present the main features of the spin-orbital superexchange which describes the magnetic and optical properties of Mott insulators with orbital degrees of freedom. In contrast to the SU(2)...
Reiter's polaron wavefunction applied to a $t_{2g}$ orbital t-J model (2008)
Wohlfeld, Krzysztof, Oles, Andrzej M., Daghofer, Maria, Horsch, Peter
Using the self-consistent Born approximation we calculate Reiter's wavefunction for a single hole introduced into the undoped and orbitally ordered ground state of the t-J model with $t_{2g}$ orbital...
Spectral properties of orbital polarons in Mott insulators (2008)
Wohlfeld, Krzysztof, Daghofer, Maria, Oles, Andrzej M., Horsch, Peter
We address the spectral properties of Mott insulators with orbital degrees of freedom, and investigate cases where the orbital symmetry leads to Ising-like superexchange in the orbital sector. The...
Superconductivity of Mo3Sb7 from first principles (2008)
Wiendlocha, Bartlomiej, Tobola, Janusz, Sternik, Malgorzata, Kaprzyk, Stanislaw, Parlinski, Krzysztof, Oles, Andrzej M.
Superconductivity in Mo3Sb7 is analyzed using the combined electronic structure and phonon calculations, and the electron--phonon coupling constant \lambda_{ph}=0.54 is determined from first...
Quantum Phase Transition in the One-Dimensional XZ Model (2008)
Brzezicki, Wojciech, Oles, Andrzej M.
We introduce a one-dimensional (1D) XZ model with alternating $\sigma_i^z\sigma_{i+1}^z$ and $\sigma_i^x\sigma_{i+1}^x$ interactions on even/odd bonds, interpolating between the Ising model and the...
Normand, Bruce, Oles, Andrzej M.
We consider the spin--orbital model for a magnetic system with singly occupied but triply degenerate $t_{2g}$ orbitals coupled into a planar, triangular lattice, as would be exemplified by NaTiO$_2$....
Piekarz, Przemyslaw, Parlinski, Krzysztof, Oles, Andrzej M.
The Verwey phase transition in magnetite has been analyzed using the group theory methods. It is found that two order parameters with the symmetries $X_3$ and $\Delta_5$ induce the structural...
Unidirectional d-wave superconducting domains in the two-dimensional t-J model (2007)
Raczkowski, Marcin, Capello, Manuela, Poilblanc, Didier, Fresard, Raymond, Oles, Andrzej M.
Motivated by the recently observed pattern of unidirectional domains in high-T_c superconductors [Y. Kohsaka et al., Science 315, 1380 (2007)], we investigate the emergence of spontaneous modulations...
One-dimensional orbital fluctuations and the exotic magnetic properties of YVO$_3$ (2007)
Oles, Andrzej M., Horsch, Peter, Khaliullin, Giniyat
Starting from the Mott insulator picture for cubic vanadates, we derive and investigate the model of superexchange interactions between V$^{3+}$ ions, with nearly degenerate $t_{2g}$ orbitals...
Spin-orbital entanglement near quantum phase transitions (2007)
Oles, Andrzej M., Horsch, Peter, Khaliullin, Giniyat
Spin-orbital entanglement in the ground state of a one-dimensional SU(2)$\otimes$SU(2) spin-orbital model is analyzed using exact diagonalization of finite chains. For $S=1/2$ spins and $T=1/2$...
Orbital liquid in ferromagnetic manganites: The orbital Hubbard model for $e_g$ electrons (2007)
Feiner, Louis Felix, Oles, Andrzej M.
We have analyzed the symmetry properties and the ground state of an orbital Hubbard model with two orbital flavors, describing a partly filled spin-polarized $e_g$ band on a cubic lattice, as in...
Wohlfeld, Krzysztof, Oles, Andrzej M., Sawatzky, George A.
We formulate a d-p multiband charge transfer model for Cu$_2$O$_5$ coupled spin ladders, relevant for Cu$_2$O$_3$ plane of Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$, and solve it using Hartree-Fock...
Spin-rotationally symmetric domain flux phases in underdoped cuprates (2007)
Raczkowski, Marcin, Poilblanc, Didier, Fresard, Raymond, Oles, Andrzej M.
We propose a new form of inhomogeneous phases consisting of out-of-phase staggered flux domains separated by diagonal charged domain walls centered on bonds or on sites. Remarkably, such domain flux...
Quantum phase transition in the one-dimensional compass model (2007)
Brzezicki, Wojciech, Dziarmaga, Jacek, Oles, Andrzej M.
We introduce a one-dimensional model which interpolates between the Ising model and the quantum compass model with frustrated pseudospin interactions $\sigma_i^z\sigma_{i+1}^z$ and...
Charge density wave in the spin ladder of Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$ (2006)
Wohlfeld, Krzysztof, Oles, Andrzej M., Sawatzky, George A.
We consider a multiband charge transfer model for a single spin ladder describing the holes in Sr$_{14-x}$Ca$_x$Cu$_{24}$O$_{41}$. Using Hartree-Fock approximation we show how the charge density...
Raczkowski, Marcin, Fresard, Raymond, Oles, Andrzej M.
Using a spin-rotation invariant version of the slave-boson approach we investigate the relative stability and band structure of various incommensurate phases in the cuprates. Our findings obtained in...
Mechanism of the reorientation of stripes in the cuprates (2006)
Raczkowski, Marcin, Fresard, Raymond, Oles, Andrzej M.
Using the mean field theory in the slave-boson approach we analyzed the electron correlation effects in the stripe phases. One finds that a finite next-nearest neighbor hopping $t'$ plays an...
Spin-rotationally symmetric domain flux phases in underdoped cuprates (2006)
Raczkowski, Marcin, Poilblanc, Didier, Fresard, Raymond, Oles, Andrzej M.
We propose a new form of inhomogeneous phases consisting of out-of-phase staggered flux domains separated by diagonal charged domain walls centered on bonds or on sites. Remarkably, such domain flux...
Magnetic and orbital correlations in a two-site molecule (2006)
Raczkowski, Marcin, Fresard, Raymond, Oles, Andrzej M.
We analyze the role of orbital degeneracy in possible magnetic and orbital instabilities by solving exactly a two-site molecule with two orbitals of either $e_g$ or $t_{2g}$ symmetry at...
Interplay between incommensurate phases in the cuprates (2006)
Raczkowski, Marcin, Fresard, Raymond, Oles, Andrzej M.
We establish the qualitative behavior of the incommensurability $\epsilon$, optimal domain wall filling $\nu$ and chemical potential $\mu$ for increasing doping by a systematic slave-boson study of...
Slave-boson approach to the metallic stripe phases with large unit cells (2006)
Raczkowski, Marcin, Fresard, Raymond, Oles, Andrzej M.
Using a rotationally invariant version of the slave-boson approach in spin space we analyze the stability of stripe phases with large unit cells in the two-dimensional Hubbard model. This approach...
Spin-Orbital Entanglement and Violation of the Goodenough-Kanamori Rules (2006)
Oles, Andrzej M., Horsch, Peter, Feiner, Louis Felix, Khaliullin, Giniyat
We point out that large composite spin-orbital fluctuations in Mott insulators with $t_{2g}$ orbital degeneracy are a manifestation of quantum entanglement of spin and orbital variables. This results...
Double exchange model in cubic vanadates (2006)
Wohlfeld, Krzysztof, Oles, Andrzej M.
We investigate the role of the double exchange mechanism for stability of the metallic C-type antiferromagnetic (C-AF) phase, which was observed experimentally in hole doped La$_{1-x}$Sr$_x$VO$_3$....
Microscopic origin of diagonal stripe phases in doped nickelates (2006)
Raczkowski, Marcin, Fresard, Raymond, Oles, Andrzej M.
We investigate the electron density distribution and the stability of stripe phases in the realistic two-band model with hopping elements between e_g orbitals at Ni sites on the square lattice, and...
Oles, Andrzej M., Khaliullin, Giniyat, Horsch, Peter, Feiner, Louis Felix
The temperature dependence and anisotropy of optical spectral weights associated with different multiplet transitions is determined by the spin and orbital correlations. To provide a systematic basis...
Stripe phases - possible ground state of the high-Tc superconductors (2005)
Raczkowski, Marcin, Oles, Andrzej M., Fresard, Raymond
Based on the mean-field method applied either to the extended single-band Hubbard model or to the single-band Peierls-Hubbard Hamiltonian we study the stability of both site-centered and...
Circulating-current states and ring-exchange interactions in cuprates (2004)
We consider the consequences for circulating-current states of a cyclic, four-spin, ``ring-exchange'' interaction of the type shown recently to be significant in cuprate systems. The real-space...
Theory of optical spectral weights in Mott insulators with orbital degrees of freedom (2004)
Khaliullin, Giniyat, Horsch, Peter, Oles, Andrzej M.
Introducing partial sum rules for the optical multiplet transitions, we outline a unified approach to magnetic and optical properties of strongly correlated transition metal oxides. On the example of...
Dimerization versus Orbital Moment Ordering in the Mott insulator YVO$_3$ (2003)
Horsch, Peter, Khaliullin, Giniyat, Oles, Andrzej M.
We use exact diagonalization combined with mean-field theory to investigate the phase diagram of the spin-orbital model for cubic vanadates. The spin-orbit coupling competes with Hund's exchange and...
Jahn-Teller Effect and Superexchange in Half-Doped Manganites (2003)
Sikora, Olga, Oles, Andrzej M.
We investigate the stability of the charge exchange (CE) phase within a microscopic model which describes a single plane as in La$_{0.5}$Sr$_{1.5}$MnO$_4$. The model includes Coulomb interactions...
Origin of the Orbital Ordering in LaMnO$_3$ (2003)
Sikora, Olga, Oles, Andrzej M.
We use the temperature of the structural phase transition to determine the Jahn-Teller (JT) coupling constant in the model derived for LaMnO$_3$ which includes both the superexchange between S=2...
Orbital Ordering and Orbital Fluctuations in Transition Metal Oxides (2003)
We summarize some characteristic features of the frustrated magnetic interactions in spin-orbital models adequate for cubic transition metal oxides with orbital degeneracy. A generic tendency towards...
Origin of the Optical Gap in Half-Doped Manganites (2002)
Cuoco, Mario, Noce, Canio, Oles, Andrzej M.
We have analyzed the coexisting charge and orbital ordering in half-doped manganites using a model which includes Coulomb and Jahn-Teller orbital polarization interactions. Most surprisingly, the gap...
Magnetic Order in Transition Metal Oxides with Orbital Degrees of Freedom (2002)
We investigate the frustrated magnetic interactions in cubic transition metal oxides with orbital degeneracy. The $e_g$ orbitals order easier and their ordering explains the $A$-type...
Photoemission spectra of LaMnO3 controlled by orbital excitations (2001)
Brink, Jeroen Van Den, Horsch, Peter, Oles, Andrzej M.
We investigate the spectral function of a hole moving in the orbital-ordered ferromagnetic planes of LaMnO$_3$, and show that it depends critically on the type of orbital ordering. While the hole...
Quantum Decoherence in the Spectral Functions of Undoped LaMnO3 (2001)
Bala, Jan, Macridin, Alexandru, Oles, Andrzej M., Sawatzky, George A.
Magnetic phases near the Van Hove singularity in s- and d-band Hubbard model (1999)
Fleck, Marcus, Oles, Andrzej M., Hedin, Lars
We investigate the magnetic instabilities of the nondegenerate (s-band) and a degenerate (d-band) Hubbard model in two dimensions using many-body effects due to the particle-particle diagrams and...
Fleck, Marcus, Lichtenstein, Alexander I., Oles, Andrzej M., Hedin, L.
We present spectral and optical properties of the Hubbard model on a two-dimensional square lattice using a generalization of dynamical mean-field theory to magnetic states in finite dimension. The...
Oles, Andrzej M., Feiner, Louis Felix, Zaanen, Jan
We study the effective spin-orbital model derived for the d9 ions in a three-dimensional perovskite lattice, as in KCuF_3, where at each site the doubly degenerate eg orbitals contain a single hole....
Orbital dynamics in ferromagnetic transition metal oxides (1998)
Brink, Jeroen Van Den, Horsch, Peter, Mack, Frank, Oles, Andrzej M.
We consider a model of strongly correlated $e_g$ electrons interacting by superexchange orbital interactions in the ferromagnetic phase of LaMnO$_3$. It is found that the classical orbital order with...
Quantum disorder versus order-out-of-disorder in the Kugel-Khomskii model (1998)
Feiner, Louis Felix, Oles, Andrzej M., Zaanen, Jan
The Kugel-Khomskii model, the simplest model for orbital degenerate magnetic insulators, exhibits a zero temperature degeneracy in the classical limit which could cause genuine quantum disorder....
Electronic origin of magnetic and orbital ordering in insulating LaMnO_3 (1998)
Feiner, Louis Felix, Oles, Andrzej M.
We derive a spin-orbital model for insulating LaMnO_3 which fulfills the SU(2) symmetry of S=2 spins at Mn^{3+} ions. It includes the complete e_g and t_{2g} superexchange which follows from a...
Quantum Melting of Magnetic Order due to Orbital Fluctuations (1997)
Feiner, Louis Felix, Oles, Andrzej M., Zaanen, Jan
We have studied the phase diagram and excitations of the spin-orbital model derived for a three dimensional perovskite lattice, as in KCuF_3. The results demonstrate that the orbital degeneracy...