Phase change observed in ultrathin BaSrTiO films by in situ resonant photoemission spectroscopy

Lin, Y.-H.*; Terai, Kota*; Wadachi, Hiroki*; Kobayashi, Masaki*; Takizawa, Masaru*; Hwang, J. I.*; Fujimori, Atsushi; Nan, C.-W.*; Li, J.-F.*; Fujimori, Shinichi   ; Okane, Tetsuo  ; Saito, Yuji  ; Kobayashi, Keisuke*

Epitaxial BaSrTiO thin films were prepared on Nb-doped SrTiO (100) substrates by the pulsed laser deposition technique and were studied by measuring the Ti 2p 3d resonant photoemission spectra in the valence-band region, both at room temperature and low temperature. The results demonstrated an abrupt variation in the spectral structures between 2.8 nm (7 ML) and 2.0 nm (5 ML) BaSrTiO films, suggesting that there exists a critical thickness for phase change in the range of 2.0-2.8 nm.