Effects of uniaxial strain in (formula presented)

The effects of uniaxial strain on the structural, orbital, optical, and magnetic properties of (formula presented) are calculated using realistic expressions for elastic energies, along with a tight-binding parametrization of the band theory and electron-phonon coupling. Tensile uniaxial strain of the order of 2% (i.e., of the order of magnitude of those induced in thin films by lattice mismatch with substrates) is found to change the magnetic ground state, causing dramatic changes in the band structure and optical conductivity spectrum. Related issues, including reasons why the observed (ππ0) orbital ordering is favored over a (πππ) periodicity and why the uniform tetragonal distortion mode is softer in insulating than in doped compounds, are discussed.