Electronic and vibrational properties of the low-dimensional perovskites Sr1-yLayNbO3.5-x

By angle-resolved photoemission spectroscopy and polarization-dependent infrared reflectivity measurements the electronic and vibrational properties of the low-dimensional perovskites Sr1-yLayNbO3.5-x were studied along different crystal directions. The electronic behavior strongly depends on the oxygen and La content, including quasi-one-dimensional metallic and ferroelectric insulating behavior. An extremely small energy gap at the Fermi level is found for SrNbO3.41 and SrNbO3.45 along the conducting direction at low temperature, suggestive for a Peierls-type instability. Despite the similar nominal carrier density, for Sr0.8La0.2NbO3.50 the quasi-one-dimensional metallic character is suppressed and no gap opening is observed, which can be explained by differences in the crystal structure. Electron-phonon interaction appears to play an important role in this series of compounds.