A. Yamanaka

Angle-resolved inverse photoemission study of Bi2Sr2CaCu2O8: Existence of two CuO2 bands across the Fermi level

Abstract Angle-resolved inverse photoemission spectroscopy was performed on a Bi 2 Sr 2 CaCu 2 O 8 single crystal to study the electronic structure in the vicinity of the Fermi level. Inverse photoemission intensity shows two maxima at about 0.21 ΓX and 0.6ΓX from the Γ point along the ΓX direction, suggesting that there are two bands crossing the Fermi level. The present experimental result was compared with angle-resolved photoemission results and band structure calculations.

Electronic Raman scattering spectra of Sr2RuO4 single crystals

Abstract Electronic Raman scattering has been measured in Sr 2 RuO 4 single crystals. We observe that the electronic Raman scattering exhibits a structureless continuum spectrum extending to beyond 4000 cm −1 . The scattering rate Γ of charge carriers, estimated from the observed Raman spectrum, shows an ω-linear increase in the higher-energy region above 500 cm −1 . This indicates strong correlation between charge carriers. In the lower-energy region the scattering rate is almost constant, Γ (0) ∼ 300 cm −1 . This value is essentially the same as that observed in high- T c copper oxides.

Hyperfine fields and quadrupole frequencies at each Cu site in RBa2Cu3O6 and RBa2Cu3O7 (R: rare earth element)

Abstract Hyperfine field at the Cu(2) site and quadrupole frequencies of both the Cu(1) and Cu(2) sites in RBa 2 Cu 3 O 6 and RBa 2 Cu 3 O 7 (R is a rare earth element) obtained from the Cu-NQR and antiferromagnetic nuclear resonance (AFNMR) are summarized as a function of the rare earth ionic radius.

High-resolution oxygen-K absorption study of Bi2Sr2Ca1−xYxCu2O8 (x=0.0 and 0.6) and YBa2Cu2O7−δ (δ=0.0−0.7)

Abstract High-energy-resolved oxygen K absorption spectra of Bi2Sr2Ca1−xYxCu2O8 (x=0.0 and 0.6) single crystals and YBa2Cu3O7−δ ( δ =0.0−0.7) ceramics were reported. The experimental results show that (1) the electronic states at the Fermi level in superconductor has a dominant O2p x,y symmetry, (2) the lowest unoccupied states in nonsuperconductor is located about 1 eV above the Fermi level and also has a strong in-plane symmetry, and (3) hole-doping causes a transfer of weight of the electronic states from the lowest unoccupied states (upper Hubbard band) to the mid-gap states produced by hole-doping at the Fermi level.

Raman scattering in YBa2Cu3O7 single crystals: anisotropy in normal and superconductivity states

Precise temperature and polarization dependences of Raman spectra have been investigated for fully oxygenated twin-free YBa2Cu3O7 single crystals. We have found a striking superconductivity-induced x−y anisotropy in the temperature behavior of the 340 cm−1 line: the magnitudes of the softening and broadening are quite different in the xx-and yy-polarizations. This anisotropy suggests a contribution of the CuO-chain superconductivity with a pairing symmetry different from that for the CuO2 plane, or indicates that the superconducting gap amplitudes are different in the kx and ky directions. The d+s gap symmetry is the only realistic symmetry in the case of Δx≠Δy.

Raman scattering from electronic excitations in high-Tc copper-oxides

Abstract We report temperature dependence of the electronic Raman scattering in high-Tc copper oxide Bi2Sr2CaCu2O2+δ. The variation of the electronic Raman spectrum below Tc reflects not only the superconducting gap, hut also the condensation of thermally excited quasiparticles to the superconductinggroundstate. The former exhibits a significant variation only just below Tc, which is quite different from the temperature dependence of the gap predicted from weak-coupling BCS theory. In contrast, the superconducting condensation occurs almost over the whole temperature region of the superconducting phase. Further, we report the electronic Raman scattering in oxygen-deficient Bi2Sr2CaCu2O2+δ. Both tetragonal A1g and B1g scatterings exhibit a continuum spectrum with a broad peak at low temperatures. As compared to the spectrum of Tc~90K Bi2Sr2CaCu2O2 + δ, the redistribution of the continuum is incomplete, suggesting the existence of normal-state carriers. Remarkably, the A1g peak energy does not depend significantly on oxygen content, which is basically inconsistent with behaviour of the gap expected from BCS theory. We discuss the oxygenconcentration dependence of the electronic Raman scattering.

Dimensionality, Tc and Cu-site substitution effect of iodine-intercalated and oxidized Bi2Sr2CaCu2O8+δ: Interpretation by the multilayer model

Abstract Changes of the dimensionality and Tc through iodine intercalation and oxidation have been studied in Bi2Sr2CaCu2O8+δ single crystals. Both intercalation and oxidation change the dimensionality of the physical properties from pseudo-two-dimensional to three-dimensional and decrease Tc. These effects are explained by the multilayer model, where a high-Tc cuprate is regarded as an alternating stack of CuO2 layers (superconducting layers) and block layers (normal layers), taking into account the proximity effect. The Tc-suppression by Cu-site substitution has also been studied for iodine-intercalated and pristine Bi2Sr2Ca(Cu1−zCoz)2O8+δ polycrystals with different δ-values.