  We have synthesized epitaxial Sr2IrO4 thin-films on various substrates and
studied their electronic structures as a function of lattice-strains. Under
tensile (compressive) strains, increased (decreased) Ir-O-Ir bond-angles are
expected to result in increased (decreased) electronic bandwidths. However, we
have observed that the two optical absorption peaks near 0.5 eV and 1.0 eV are
shifted to higher (lower) energies under tensile (compressive) strains,
indicating that the electronic-correlation energy is also affected by in-plane
lattice-strains. The effective tuning of electronic structures under
lattice-modification provides an important insight into the physics driven by
the coexisting strong spin-orbit coupling and electronic correlation.
