Variation of the electronic structure in systematically synthesized Sr2MO4 (M=Ti, V, Cr, Mn, and Co) -: art. no. 176404

We have systematically synthesized single-crystalline thin films of layered perovskites Sr2MO4 (M=Ti, V, Cr, Mn, and Co) which cannot be obtained in a form of bulk crystal apart from M=Mn. The two-dimensional electronic structure of these M4+ oxides, ranging from a correlated insulator to a ferromagnetic metal, has been investigated by using their optical conductivity spectra with polarizations E perpendicular to c and E parallel to c, which reveal systematic variation of the correlated charge gap, Mott-Hubbard gap, or charge-transfer gap. Temperature dependence of the gap-transition spectra is argued in the light of possible spin and/or orbital ordering.