  We have performed angle-resolved photoemission spectroscopy (ARPES)
measurements and first-principles electronic structure calculations on the
electron-doped high-Tc superconductors Ln1.85Ce0.15CuO4 (Ln = Nd, Sm, and Eu).
The observed Fermi surface and band dispersion show such changes that with
decreasing ionic size of Ln3+, the curvature of the Fermi surface or -t'/t
decreases, where t and t' are transfer integrals between the nearest-neighbor
and next-nearestneighbor Cu sites, respectively. The increase of t with
chemical pressure is found to be significant, which may explain the apparently
inconsistent behavior seen in the hole-doped La2-xSrxCuO4 under epitaxial
strain [M. Abrecht et al., Phys. Rev. Lett. 91, 057002 (2003)]. A gap due to
the antiferromagnetism opens even in the nodal region for the Sm and Eu
compounds, and the gap size increases in going from Ln = Sm to Eu.
