arXiv subjects

Satoshi Okamoto

Publications and source records attributed to Satoshi Okamoto.

113 records · Page 7Linked to original sources

arXiv2004

Theory of Mott insulator/band insulator heterostructure

A theory of heterostructures comprised of LaTiO$_3$ (a Mott insulator) and SrTiO$_3$ (a band insulator) is presented. The band structure of the Ti $d$% -electrons is treated with a nearest neighbor tight-binding approximation; the electric fields arising from the La$^{3+}$/Sr$^{2+}$ charge difference and the carriers are treated within a Hartree approximation; and the on-site interactions are treated by unrestricted Hartree-Fock. The phase diagram as a function of interaction strength and layer number is determined and predictions are made for optical conductivity experiments. A note worthy finding is that the edges of the heterostructure are generally metallic.

cond-mat.str-el↗

arXiv2004

Electron-lattice coupling, orbital stability and the phase diagram of Ca$_{2-x}$Sr$_x$RuO$_4$

Hartree-Fock calculations are presented of a theoretical model describing the Sr/CaRuO$_4$ family of compounds. Both commensurate and incommensurate magnetic states are considered, along with orbital ordering and the effect of lattice distortions. For reasonable parameter values, interactions disfavor orbital disproportionation. A coherent description of the observed phase diagram is obtained.

cond-mat.str-el↗

arXiv2002

Quantum behavior of Orbitals in Ferromagnetic Titanates: Novel Orderings and Excitations

We investigate the collective behavior of orbital angular momentum in the spin ferromagnetic state of a Mott insulator with $t_{2g}$ orbital degeneracy. The frustrated nature of the interactions leads to an infinite degeneracy of classical states. Quantum effects select four distinct orbital orderings. Two of them have a quadrupolar order, while the other states show in addition weak orbital magnetism. Specific predictions are made for neutron scattering experiments which might help to identify the orbital order in YTiO$_3$ and to detect the elementary orbital excitations.

cond-mat.str-el↗

arXiv2001

Re-examination of orbital ordering in LaMnO$_3$: Electron-electron and electron-lattice interactions

The interactions between $e_g$ orbitals in neighboring sites are investigated in LaMnO$_3$ by taking into account virtual exchange of electrons and phonons. The spin and orbital ordering temperatures and the spin wave dispersion relation are calculated. We find that the orbital ordering is mainly caused by the electronic interactions and that the Jahn-Teller coupling is much smaller than that reported previously. We propose that the elastic constant shows a characteristic change at the N{é}el temperature by the spin and orbital coupling and the higher-order Jahn-Teller coupling.

cond-mat.str-el↗

arXiv1997

Pressure Effects in Manganites with Layered Perovskite Structure

Pressure effects on the charge and spin dynamics in the bilayer manganite compounds $La_{2-2x}Sr_{1+2x}Mn_2O_7$ are studied theoretically by taking into account the orbital degrees of freedom. The orbital degrees are active in the layered crystal structure, and applied hydrostatic pressure stabilizes the $3d_{x^2-y^2}$ orbital in comparison with $3d_{3z^2-r^2}$. The change of the orbital states weakens the interlayer charge and spin couplings, and suppresses the three dimensional ferromagnetic transition. Numerical results, based on an effective Hamiltonian which includes the energy level difference of the orbitals, show that the applied pressure controls the dimensionality of the spin and charge dynamics through changes of the orbital states.

cond-mat.str-el↗