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Oral presentation

Polaronic effect in lightly doped high-Tc cuprates

Sakai, Toru

no journal, ,

The phonon effect of the in-plane oxygen atoms is investigated by the numerical exact diagonalization method of the finite-cluster extended t-J Holstein model. In the previous study the buckling vibration possibly assists the superconductivity, while the breathing one would lead to some static orderings. In the present work we investigate the polaronic effect on the quasiparticle dynamics and discuss on the anomalous behavior observed in the recent experiments of the angle-resolved photoemission spectroscopy.

Oral presentation

Phase competitions and phase coexistences in quasi-one-dimensional molecular conductors

Seo, Hitoshi; Kato, Takeo*; Motome, Yukitoshi*

no journal, ,

We have theoretically investigated finite-temperature properties ofIn this work, we aim at providing a unified view for such compounds by studying a quasi-one-dimensional model numerically, whose Hamiltonian iswritten as ${cal H}_{rm 1D} + {cal H}_{perp} + {cal H}_{rm e-l}$ . The first term ${cal H}_{rm 1D}$ is the one-dimensional extended Hubbard model in the chain direction, the second term ${cal H}_{perp}$ denotes the interchain interactions such as the Coulomb repulsion and the exchange coupling, and the third term ${cal H}_{rm e-l}$ represents the electron-lattice interaction. We use two methods to treat this model. One is the transfer matrix method applied to the effective one-dimensional model by treating ${cal H}_{perp}$ within the "interchain mean-field" approximation. Another is the quantum Monte Carlo simulation with stochastic series expansionwhere the interchain interactionsas well as thermal fluctuations of lattice distortions can be taken into account in an unbiased way. We will compare the numerical results with the experimental dataso as to elucidate the origin of the various properties seen in the actual compounds.

Oral presentation

Phonon softening in boron doped diamond

Fukuda, Tatsuo; Hoesch, M.*; Takenouchi, Tomohiro*; Sutter, J. P.*; Tsutsui, Satoshi*; Baron, A.*; Nagao, Masanori*; Takano, Yoshihiko*; Kawarada, Hiroshi*; Mizuki, Junichiro

no journal, ,

Diamond is well known for its maximum hardness, large energy gap, high thermal conductivity, and so on. In addition to these, the superconductivity was discovered recently in boron doped (B-doped) diamond, and this was soon confirmed by other groups. We performed inelastic X-ray scattering experiments at BL35XU of SPring-8 to measure phonons in a highly B-doped CVD grown diamond having superconducting transition at 4.2 K. By comparing the experimental results with those from nitrogen doped CVD grown diamond and/or pure diamond, we found that the optical modes are softened especially at around the Brillouin zone center along with a strong broadening, while the acoustic modes do not show both softening and broadening. This confirms the strong electron-phonon coupling in superconducting diamond.

Oral presentation

Charge excitations in (La,Sr,Ca) $_{14}$ Cu $_{24}$ O $_{41}$ studied by resonant inelastic X-ray scattering

Ishii, Kenji; Tsutsui, Kenji*; Toyama, Takami*; Mizuki, Junichiro; Endo, Yasuo; Maekawa, Sadamichi*; Kudo, Kazutaka*; Koike, Yoji*; Kumagai, Kenichi*

no journal, ,

(La,Sr,Ca) $_{14}$ Cu $_{24}$ O $_{41}$ is an attractive material in connection with high- $T_{rm c}$ superconductivity because Sr $_{0.4}$ Ca $_{13.6}$ Cu $_{24}$ O $_{41}$ becomes a superconductor under high pressure without the CuO planes. We present RIXS at the Cu -edge of (La,Sr,Ca) $_{14}$ Cu $_{24}$ O $_{41}$ focusing on the momentum dependence of interband excitation across the Mott gap and the intraband excitation below the gap as a function of hole concentration. The experimental results are consistent with the theoretical predictions.