Coherent and Incoherent Excitations of Electron-DopedSrTiO3

Abstract

Resonant photoemission at the Ti 2p and O 1s edges on a Nb-doped SrTiO3 thin film revealed that the coherent state (CS) at the Fermi level (EF) had mainly Ti 3d character whereas the incoherent in-gap state (IGS) positioned ∼1.5 eV below EF had mixed character of Ti 3d and O 2p states. This indicates that the IGS is formed by a spectral-weight transfer from the CS and subsequent spectral-weight redistribution through d-p hybridization. We discuss the evolution of the excitation spectrum with 3d band filling and rationalize the IGS through a mechanism similar to that proposed by Haldane and Anderson. PACS numbers:SrTiO 3 (STO) is a perovskite-type oxide semiconductor with a band gap of 3.2 eV [1] and is considered to be one of the promising device materials in "oxide electronics." A variety of transition-metal oxides can be grown on STO with atomical flatness to show novel phenomena such as the high-mobility and magnetic interface of

Fabrication, Characterization, and Modulation of Functional Nanolayers

“…© 2017 AIP ionic radii in the crystal structure and used Shannon's ionic radii as a comparison [23]: Ti 4+ (60.5 pm), Ti 3+ (67.0 pm), Nb 4+ (68.0 pm), and Nb 5+ (64.0 pm). In the ranges of 0.05 ≤ x ≤ 0.3 and x ≥ 0.6, the observed lattice parameters closely follow the heterovalent substitution line, suggesting that two Ti 4+ or Nb 4+ ions are substituted by adjacent (Ti 3+ /Nb 5+ ) ions [24]. On the other hand, at x = 0.4 and 0.5, the observed lattice parameter correspond well with the isovalent substitution line.…”

Structure and correlation effects in semiconductingSrTiO3

“…3͒ suggest that the electron-phonon coupling might play an important role for the thermoelectricity in doped STO. While the conduction-band structure of the n-doped STO was previously extracted using the photoemission spectroscopy [19][20][21][22] as well as the magnetotransport, 17,18 the precise evaluation of the Fermi-surface shape, effective mass, and electron-phonon interaction from ARPES bandstructure measurements is unique to the present study. The present work is only possible because of the very high energy and momentum resolution of the experiments that also cover several Brillouin zones of STO.…”

Electronic Reconstruction at the Interface Between Band Insulating Oxides: The LaAlO3/SrTiO3 System

“…Assuming one electron per site, the fraction of 0.4 e -/uc counted by STS spectroscopy is not far from the 0.5 e -/uc predicted by the electrostatic instability scenario. Moreover, electrons in these in-gap states have energy quite far from the Fermi level and from the 3d-Ti conduction bands, thus they have probably mixed Ti3d and O2p character, as it happens at the STO surface [73]; this interpretation is consistent with the fact that the fraction of observed Ti 3+ is much lower than the value expected, since electrons are not localized in Ti 3+ states, but in states which are obtained from the hybridization between O2p and Ti-3d orbitals. …”