arXiv subjects

Yoshiaki Ōno

Publications and source records attributed to Yoshiaki Ōno.

23 records · Page 2Linked to original sources

arXiv2009

Quadrupole Susceptibility and Elastic Softening due to a Vacancy in Silicon Crystal

We investigate the electronic states around a single vacancy in silicon crystal by using the Green's function approach. The triply degenerate vacancy states within the band gap are found to be extended over a large distance $\sim20 {\rm Å}$ from the vacancy site and contribute to the reciprocal temperature dependence of the quadrupole susceptibility resulting in the elastic softening at low temperture. The Curie constant of the quadrupole susceptibility for the trigonal mode ($O_{yz},O_{zx},O_{xy}$) is largely enhanced as compared to that for the tetragonal mode ($O_{2}^{0},O_{2}^{2}$). The obtained results are consistent with the recent ultrasonic experiments in silicon crystal down to 20 mK. We also calculate the dipole and octupole susceptibilities and find that the octupole susceptibilities are extremely enhannced for a specific mode.

cond-mat.other↗

arXiv2008

Magnetism and Superconductivity in the Two-Dimensional 16 Band d-p Model for Iron-Based Superconductors

The electronic states of the Fe2As2 plane in iron-based superconductors are investigated on the basis of the two-dimensional 16-band d-p model which includes the Coulomb interaction on a Fe site: the intra- and inter-orbital direct terms U and U', the Hund's coupling J and the pair-transfer J'. Using the random phase approximation (RPA), we obtain the magnetic phase diagram including the stripe and the incommensurate order on the U'-J plane. We also solve the superconducting gap equation within the RPA and find that, for large J, the most favorable pairing symmetry is extended s-wave whose order parameter changes its sign between the hole pockets and the electron pockets, while it is dxy-wave for small J.

cond-mat.str-el↗

arXiv2008

Successive Phase Transitions in Na_{0.5}CoO_{2} based on the Triangular Lattice d-p Model

We investigate the electronic states of the CoO_2 plane in the layered cobalt oxides Na_{0.5}CoO_{2} using the realistic 11 band d-p model on a two-dimensional triangular lattice. Effects of the Coulomb interaction on a Co site: the intra- and inter-orbital direct terms U and U', the exchange coupling J and the pair-transfer J', are treated within the Hartree-Fock approximation. It is found that the metallic antiferromagnetism takes place below T_{c1} and, in addition, the orbital order accompanied by the small charge order takes place below T_{c2} (< T_{c1}) where the system becomes insulator. The obtained results are consistent with the successive phase transitions observed in Na_{0.5}CoO_{2}.

cond-mat.str-el↗

arXiv2001

Critical Behaviour near the Mott Transition in a Two-Band Hubbard Model

The Mott metal-insulator transition in the two-band Hubbard model in infinite dimensions is studied by using the linearized dynamical mean-field theory. The discontinuity in the chemical potential for the change from hole to electron doping is calculated analytically as a function of the on-site Coulomb interaction $U$, and the charge-transfer energy $Δ$ between the $d$- and $p$-orbitals, transfer integrals $t_{pd}$, $t_{pp}$, $t_{dd}$ between $p$-$d$, $p$-$p$ and $d$-$d$ sites respectively. The critical behaviour of the quasiparticle weight is also obtained analytically.

cond-mat.str-el↗

arXiv1994

Phase diagrams of electronic state on One Dimensional d-p Model

We investigate the one-dimensional(1D) d-p model, simulating a Cu-O linear chain with strong Coulomb repulsion, by using the numerical diagonalization method. Using the Luttinger liquid theory, we obtained phase diagrams of the ground state on $U_d-U_{pd}$ plane, where $U_d$ and $U_{pd}$ represent on-site interaction at d-sites and the nearest-neighbor interaction between p- and d-sites respectively. In the weak coupling region, they agree with the g-ology; a superconducting phase (SC(I)) is restricted to attractive interaction $U_{pd}<0$. On the other hand, in the strong coupling region, we found a novel superconducting phase(SC(II)) for repulsive interaction $U_{pd}>|U_d|$ and a insulating state with a charge gap for $U_d>U_d^c$ and $U_{pd}>U_{pd}^c$ with critical values $U_d^c$ and $U_{pd}^c$ at half-filling. Away from half-filling, another superconducting phase (SC(III)) appears for $U_d>>U_{pd}>0$; which has been found for $U_d\to \infty$ in the previous paper [Physica {\bf C205} (1993) 170]. An analysis of the spin gap suggests that the SC(I) and SC(II) include the Luther-Emery region (with spin-gap) in part, while the SC(III) belongs to Tomonaga-Luttinger region (without spin-gap) in whole.

cond-mat↗