Orbital-driven Variation of Electronic Structures in Tetragonal La1/2Sr1/2MnO3as Investigated by Optical Spectroscopy

Optical conductivity spectra (σ(ω)) were investigated for coherently strained epitaxial films of tetragonal La 1/2 Sr 1/2 MnO 3 with various c / a ratios (1.04, 1.00, and 0.98). With decreasing c / a , σ(ω) in the ground state shows a successive dramatic change from an insulating gap-like to metallic but highly incoherent spectrum, then to a pseudo-gap one, which reflects the strain-induced e g orbital ordering/disordering and the resultant different spin structures. The variation of the electronic structure induced by such a strain-orbital coupling is discussed in comparison with some theoretical models.