T. Nishijima

Dynamic correlation function studies of the medium-range order in materials

Abstract This paper discusses the extraction of structural and dynamical information from the Q -dependence of the dynamical structure factor, S ( Q , E ), measured by inelastic neutron scattering. The analysis of data for vitreous SiO 2 is considered, and it is shown that the Q -dependence of S ( Q , E ) may be investigated either in real space by use of a dynamic correlation function (DCF) or in reciprocal space by modelling. The modelling approach provides a new means to extract the bond angle distribution, and the results obtained agree well with previous information on the bond angle distribution. The application of the DCF approach to data for a (crystalline) high T c superconductor is used to show that the DCF may provide partial structure factor information without isotope substitution when the material contains elements with different masses - a result with important potential for the study of amorphous materials.

Lattice anomaly of La1.85Sr0.15CuO4 studied by neutron scattering

Abstract Inelastic neutron scattering studies were performed on a powder and assembly of single crystals of La1.85Sr0.15CuO4. Phonon density of states and the Q-dependence of dynamic structure factor as well as the details of phonon scattering function were investigated as a function of temperature. We found specific phonon modes at the Brillouin zone center and the zone boundary showed an anomalous behavior.

Phonon anomaly of La1.85Sr0.15CuO4 studied by neutron scattering

Abstract Inelastic neutron-scattering studies were performed on a powder and an assembly of single crystals of La1.85Sr0.15CuO4, Tc ∼ 36 K. Phonon density of states and the Q-dependence of the dynamic structure factor as well, as the details of the phonon-scattering function, were investigated as a function of temperature. We found that specific phonon modes at the Brillouin zone centre and the zone boundary showed anomalous behaviour at Tc. Thus we suggest a strong correlation between the phonon states and the superconducting states.

Phonon anomaly of under-doped YBa2Cu3O6.6 studied by neutron scattering

Total Pair Correlation Function (T (r)), and phonon density of states (PDOS) were measured by neutron scattering on the powder sample of YBa2Cu3O6.6 (Tc ∼ 60K) at temperatures between 20 and 295 K. Lattice anomalies were observed in the T (r) and PDOS much above Tc as well as Tc. These results indicate that the anomaly at Tc can be related to the superconducting transition but one above Tc may be attributed to the induced lattice anomaly caused by the pseudo-spin-gap opening.

Structural instability of high-Tc superconductor La1.85Sr0.15CuO4

Investigation on a high-Tc superconductor, La1.85Sr0.15CuO4, was performed in the wide range of Q-E space by means of neutron scattering and synchrotron radiation. The structure as well as the phonon dynamics showed a clear evolution at Tc. We found a spontaneous strain and phonon softening, which proves a strong coupling between lattice and superconductivity.

Anomalous structure and phonon dynamics in La1.85Sr0.15CuO4

We performed X-ray diffraction and neutron scattering experiments on high quality single crystals of La1.85Sr0.15CuO4. We found a forbidden (1,0,0) peak, which develops below the HTT-LTO structural transition temperature, and an anomalous behavior of acoustic phonon at (2,2,0). These results indicate that the structural anomaly has a strong relation with an superconductivity.

Dynamical structural instability in YBa2Cu3O6.6

We have performed inelastic neutron scattering and total neutron scattering experiments on the under-doped superconductor YBa2Cu3O6.6. We have found that the dynamical structure and the local structure concerned about the CuO2 plane has an anomalous temperature dependence at Tc (=57K) and well above Tc (TSG∼150K), which may be explained by a spin-gap opening.

Structure and phonon anomaly in La1.85Sr0.15CuO4

We performed X-ray diffraction and neutron scattering on a single crystal La1.85Sr0.15CuO4. We found that the lattice anomaly is caused by the optical tilt phonon associated with the expansion of the c-lattice constant below Tc. We also found that the (100) peak starts to develop below the HTT-LTO structural phase transition temperature. These results suggest that there is a strong relation between the superconductivity and the structural instability.

Investigation for the dynamical and local structure of the YBa2Cu3O6.6

We have carried out inelastic neutron scattering and total neutron scattering on the typical under-doped superconductor YBa2Cu3O6.6. We have found that the dynamical structure and the local structure showed anomalous behaviors at Tc (=57K) and well above Tc (∼150K), which may be explained by a spin-gap opening.