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We have performed high-resolution ARPES on hole- and electron-doped high-Tc cuprates. We have studied the origin of dispersion kink near the Fermi level (EF) and its relation to the superconductivity. In Bi2212 and Bi2223, we found a prominent kink near (pi, 0), which shows a strong momentum and temperature dependence (1). The kink is remarkably pronounced at low temperatures, being gradually weakened on increasing temperature, and is finally vanished around superconducting transition temperature (Tc). This temperature dependence shows a good correspondence to that of the magnetic resonance mode observed by inelastic neutron scattering. We also studied the impurity effect on the kinks at (pi/2, pi/2) and (pi, 0). The former shows no change upon the substitution of Cu with Zn of about 1%, while the latter exhibits a substantial decrease in the strength. All these experimental results suggest that the magnetic interaction plays a major role in producing the kink around (pi, 0) and is closely related to the high-Tc superconductivity.
We have observed a similar kink structure in an electron-doped high-Tc cuprates, NCCO and PLCCO. In contrast to the hole-doped case, the kink is the strongest around a point just between (pi/2, pi/2) and (pi, 0), not around (pi, 0), and survives at temperatures much higher than Tc (2). This indicates that the origin of the kink in electron-doped cuprates is different from that of hole-doped ones and is probably ascribed to the band-folding due to the antiferromagnetic order/fluctuation. We also found that the superconducting gap shows the maximum at the hot spot, not around the antinode, showing the non-monotonic dx2-y2 gap symmetry in the electron-doped high-Tc cuprates (3).
(1) T. Sato et al., Phys. Rev. Lett. 91 (2003) 157003. (2) H. Matsui et al., Phys. Rev. Lett., in press. (3) H. Matsui et al., cond-mat/0411557. *This work is collaborated with T. Takahashi, H. Matsui, K. Terashima, H. Ding, T. Fujii, T. Watanabe, A. Matsuda, K. Kadowaki, and K. Yamada. |