Observation of the gap inhomogeneity in Bi2Sr2CaCu2O8+δ by laser micro-ARPES

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 extensively investigated. Angle-resolved photoemission spectroscopy (ARPES) is known as the powerful tool to prove the superconducting gap in a momentum-resolved manner, enabled fingerprinting the d-wave gap symmetry in cuprate superconductors. On the other hand, scanning tunneling spectroscopy/microscopy allows to observe the superconducting gap, and the nano-scale inhomogeneity 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 low spatial resolution (~ mm-order 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 shows the ARPES image of the underdoped Bi2212 taken along the nodal direction (red line in the 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 (blue line in the 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. 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. In this talk, we will discuss the observed real-space and momentum-space dependence on the superconducting gap and the pseudogap in detail.The 11th New Generation in Strongly Correlated Electron System