Effects of chemical pressure on the Fermi surface and band dispersion of the electron-doped high-Tc superconductors

We have performed angle-resolved photoemission spectroscopy measurements and first-principles electronic-structure calculations on the electron-doped high-T-c superconductors (HTSCs) Ln(1.85)Ce(0.15)CuO(4) (Ln=Nd, Sm, and Eu). The observed Fermi surface and band dispersion show such changes that with decreasing ionic size of Ln(3+) (increasing chemical pressure), the curvature of the Fermi surface or -t(')/t decreases, where t and t(') are transfer integrals between the nearest-neighbor and next-nearest-neighbor Cu sites, respectively, explaining the apparently inconsistent behavior seen in the hole-doped HTSC La2-xSrxCuO4 under epitaxial strain. Around the node, the antiferromagnetic gap is opened with increasing chemical pressure. We propose that the nodal gap opening is possibly due to the decrease in -t(')/t through the improved nesting, leading to the decrease in T-c.