  High quality epitaxial thin films of Jeff=1/2 Mott insulator Sr2IrO4 with
increasing in-plane tensile strain have been grown on top of SrTiO3(001)
substrates. Increasing the in-plane tensile strain up to ~0.3% was observed to
drop the c/a tetragonality by 1.2 %. X-ray absorption spectroscopy detected a
strong reduction of the linear dichroism upon increasing in-plane tensile
strain towards a reduced anisotropy in the local electronic structure. While
the most relaxed thin film shows a consistent dependence with previously
reported single crystal bulk measurements, electrical transport reveals a
charge gap reduction from 200 meV down to 50 meV for the thinnest and most
epitaxy-distorted film. We argue that the reduced tetragonality plays a major
role in the change of the electronic structure, which is reflected in the
change of the transport properties. Our work opens the possibility for
exploiting epitaxial strain as a tool for both structural and functional
manipulation of spin-orbit Mott systems.
