Sumio Ishihara

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1. Octupole order in Ce 0.7 La 0.3 B 6 probed by resonant X-ray scattering The azimuthal angle dependence observed in the resonant X-ray scattering in phase IV of Ce 0.7 La 0.3 B 6 is analyzed theoretically[1]. It is shown that the peculiar angle dependence observed in the E2 channel is consistent with the Γ 5u-type octupole order with principal axis along(More)
Electronic ferroelectricity in molecular organic crystals is reviewed from a theoretical perspective. In particular, we focus on the charge-driven-type electronic ferroelectricity where electronic charge order without inversion symmetry induces a spontaneous electric polarization in quarter-filling systems. Two necessary conditions to realize this type of(More)
A theory of doped perovskite vanadates with spin and orbital orders is presented. Mobile holes are strongly renormalized by spin excitations (magnons) in the spin G-type and orbital C-type (SG-OC) order, and orbital excitations (orbitons) in the spin C-type and orbital G-type (SC-OG) one. Hole dynamics in a staggered t(2g) orbital array is distinguished(More)
1. Consequences of multipole orders in CeB 6 and Ce x La 1−x B 6 A minimal model for multipole orders in CeB 6 is proposed and calculated by mean field theory [1, 2]. Both quadrupole and magnetic ordered phases can be reproduced with one model. From the mean field result, degeneracy of quadrupole order parameter and strong spin-orbit coupling cause(More)
Dynamical localization, that is, reduction of the intersite electronic transfer integral t by an alternating electric field, E(ω), is a promising strategy for controlling strongly correlated systems with a competing energy balance between t and the Coulomb repulsion energy. Here we describe a charge localization induced by the 9.3 MV cm(-1) instantaneous(More)
A photoinduced spin-state change in the itinerant correlated electron system is studied. A photon introduced in the low-spin band insulator induces a bound state of the high-spin state and a photoexcited hole. This bound state brings a characteristic peak in the pump-probe optical absorption spectra which are completely different from the spectra in(More)
With decreasing temperature, liquids generally freeze into a solid state, losing entropy in the process. However, exceptions to this trend exist, such as quantum liquids, which may remain unfrozen down to absolute zero owing to strong quantum entanglement effects that stabilize a disordered state with zero entropy. Examples of such liquids include(More)
Interacting orbital degrees of freedom in a Mott insulator are essentially directional and frustrated. In this Letter, the effect of dilution in a quantum-orbital system with this kind of interaction is studied by analyzing a minimal orbital model which we call the two-dimensional quantum compass model. We find that the decrease of the ordering temperature(More)
We present a theory of ultrafast photoinduced dynamics in a spin-charge coupled system, motivated by pump-probe experiments in perovskite manganites. A microscopic picture for multiple dynamics in spin and charge degrees is examined. Real-time simulations are carried out by two complimentary methods. Our calculation demonstrates that electron motion governs(More)