量研学術機関リポジトリ「QST-Repository」は、国立研究開発法人 量子科学技術研究開発機構に所属する職員等が生み出した学術成果（学会誌発表論文、学会発表、研究開発報告書、特許等）を集積しインターネット上で広く公開するサービスです。 Welcome to QST-Repository where we accumulates and discloses the academic research results(Journal Publications, Conference presentation, Research and Development Report, Patent, etc.) of the members of National Institutes for Quantum Science and Technology.
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Since the discovery of the high-Tc superconductivity in copper oxides (cuprates), the cuprate superconductors have been extensively investigated experimentally and theoretically. Nevertheless, the mechanism of the high-Tc superconductivity has not been clarified yet. The order parameter, the superconducting gap, of the high-Tc superconductivity has been particularly investigated. Angle-resolved photoemission spectroscopy is known as the powerful tool to prove the superconducting gap in a momentumresolved manner, which fingerprinted the d-wave gap symmetry. On the other hand, scanning tunneling spectroscopy/microscopy allows to observe the superconducting gap, and the nano-scale inhomogeneity was in the real-space was reported in Bi2Sr2CaCu2O8+δ (Bi2212) [1]. However, such real-space inhomogeneity has not been fully considered in the conventional ARPES studies due to its poor spatial resolution (~ mm scale). To overcome this problem and study the evolution of the superconducting gap in the real- and momentum-space, we have performed high-resolution micro-ARPES experiments on underdoped Bi2212 (Tc = 65 K) using a micro-focused laser (hν = 6 eV) at the Hiroshima Synchrotron Radiation Center, Hiroshima University.
Figure 1(a) shows the ARPES image of the underdoped Bi2212 taken along the nodal direction (see inset) in the superconducting state (T= 20 K). We have then measured such a clear band dispersion from the nodal to the off-nodal direction (see inset) and evaluated the momentum dependence of the gap. In addition, we
have also examined the real-space dependence of the superconducting gap by performing the same measurement while slightly changing the measurement position on the sample surface. Figure 1(b) compares the momentum dependence on the gap magnitude taken from the two different measurement positions (A and B). We found that the gap magnitude and its momentum dependence are clearly different in spite of the small difference (less than 0.1 mm) on the measurement position. To examine the momentum dependence quantitatively, we fit the experimental results by the gap function [2]. The fitting analysis showed that the antinodal gap for position A is larger than one for position B, while the nodal gap for position A is smaller than one for position B. In other words, our results suggest the inverse correlation between the superconducting gap and the pseudogap. In this talk, we will discuss the observed real-space and momentum-space dependence on the superconducting gap and the pseudogap in detail.
会議概要（会議名, 開催地, 会期, 主催者等）
The 25th Hiroshima International Symposium on Synchrotron Radiation
Gap inhomogeneity in Bi2Sr2CaCu2O8+δ revealed by laser micro-ARPES
