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R. Yoshizaki

Publications and source records attributed to R. Yoshizaki.

6 recordsLinked to original sources
arXiv2001

Nature of the Electronic Excitations near the Brillouin Zone Boundary of Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$

Based on angle resolved photoemission spectra measured on different systems at different dopings, momenta and photon energies, we show that the anomalously large spectral linewidth in the $(π,0)$ region of optimal doped and underdoped Bi$_2$Sr$_2$CaCu$_2$O$_{8+δ}$ has significant contributions from the bilayer splitting, and that the scattering rate in this region is considerably smaller than previously estimated. This new picture of the electronic excitation near $(π,0)$ puts additional experimental constraints on various microscopic theories and data analysis.

cond-mat.supr-con↗
arXiv2000

Signature of Superfluid Density in the Single-Particle Excitation Spectrum of Bi2Sr2CaCu2O8+delta

We report that the doping and temperature dependence of photoemission spectra near the Brillouin zone boundary of Bi2Sr2CaCu2O8+delta exhibit unexpected sensitivity to the superfluid density. In the superconducting state, the photoemission peak intensity as a function of doping scales with the superfluid density and the condensation energy. As a function of temperature, the peak intensity shows an abrupt behavior near the superconducting phase transition temperature where phase coherence sets in, rather than near the temperature where the gap opens. This anomalous manifestation of collective effects in single-particle spectroscopy raises important questions concerning the mechanism of high-temperature superconductivity.

cond-mat.supr-con↗
arXiv2000

Photoemission Studies on Bi2Sr2CaCuZnO - Electronic Structure Evolution and Temperature Dependence

An angle resolved photoelectron spectroscopy study was conducted on BiSrCaCuZnO. A small amount of Zn substitution for Cu almost completely suppresses the otherwise sharp spectral peak along the (0,0) to (pi,pi) direction in BiSrCaCuZnO, while superconductivity with Tc as high as 83K survives. This behavior contrasts markedly from that seen in cases where the impurities are located off the CuO plane, as well as when the CuO planes are underdoped. This effect is also accompanied by changes of low energy excitations at (pi,0), near the anti-node position of the d-wave pairing state. With Zn doping the size of the superconducting gap is significantly suppressed, the width of the quasiparticle peak in the superconducting state becomes wider, and the dip at higher binding energy is diminished. In addition, enhanced temperature induced spectral changes also occur. We show intriguing systematic lineshape changes with temperature that persist to a very high energy scale - a result consistent with the idea that Zn enhances the local charge inhomogeneity.

cond-mat.supr-con↗
arXiv1997

Low-Temperature Phase Transition in Bi_2Sr_2Ca(Ni_xCu_{1-x})_20_8: Evidence for Unconventional Superconductivity

We report the discovery of a low-temperature phase transition in Bi_2Sr_2Ca(Ni_xCu_{1-x})_20_8 high temperature superconductor. This transition manifests itself as a sharp reduction of the thermal conductivity of the samples at a temperature of T_c* \approx 200 mK. The temperature dependence of the thermal conductivity changes dramatically from T^αwith αbetween 1.6 and 1.75 above the transition to T-linear behavior below the transition. Application of a small magnetic field suppresses the low-temperature phase. We interpret this behavior as a phase transition into a second bulk low-temperature superconducting state in which the time-reversal symmetry is likely to be broken. This discovery constitutes direct evidence for unconventional superconductivity in high temperature superconductors.

cond-mat.supr-con↗
arXiv1997

Measurement of an Anisotropic Energy Gap in Single Plane Bi_2Sr_(2-x)La_xCuO_(6+d)

We report angle-resolved photoemission spectra both above and below T_c in the single-plane cuprate superconductor Bi_2Sr_{2-x}La_xCuO_{6+d}. The superconducting state measurements show a highly anisotropic excitation gap with a maximum magnitude smaller than that of the bilayer compound Bi_2Sr_2CaCu_2O_8 by a factor of 3. For a range of doping, the gap persists well above T_c, behavior previously associated with underdoped bilayer cuprates. The anisotropy and magnitude of the normal-state gap are very similar to the superconducting state gap, indicating that the two gaps may have a common origin in a pairing interaction.

cond-mat.supr-con↗