Photoemission study of the metallic state of lightly electron-doped SrTiO3

Coherent and Incoherent Excitations of Electron-DopedSrTiO3

“…In the O 2p band region, the higher-E B side showed stronger enhancement reflecting Ti 3d -O 2p bonding character as described by band theory [24,25,26]. The enhanced structures at hν = 458.1 eV in the near-E F region consisted of a peak at E F and a broad structure centered at ∼1.5 eV, which are the coherent states and the IGSs of doped STO, respectively [7,8,9,10,11]. We also confirmed that the resonantly enhanced IGSs were dominated by bulk character states from the take-off-angle (θ) dependence of the spectra at hν = 458.1 eV as shown in Fig.…”

“…While band theory may be a starting point to understand the transport and magnetic properties of lightlydoped STOs [6], their electronic structures near the Fermi level (E F ) are far from being doped band insulators: photoemission spectroscopy (PES) studies [7,8,9,10,11] have revealed incoherent states forming in the band gap of STO (in-gap states: IGSs) instead of a rigid shift of the bands with increasing the conduction-band filling x as schematically shown in Fig. 1(a).…”

“…However, a Hubbard model, which produces incoherent states through electron correlation as shown in Fig. 1(b), is insufficient to explain the IGSs [7,14,15] since they are observed already at x ∼ 0.05 [10] where electron correlation is expected to be small [6]. The origin of the IGSs at x ∼ 0 was attributed to chemical disorder [11], polaron effect [16], or partly to donor levels [9], but no consensus has been reached yet (see p. 1171 of [17]).…”

Structure and correlation effects in semiconductingSrTiO3

“…2͑b͒ and 2͑d͒ present clear shapes of a circle and ellipse concentrated at points. 19 The photoemission matrix element causes the intensity of each band to vary strongly from zone to zone. While no bands are visible at ⌫ 00 = ͑0,0͒, the elliptic bands are strongest at ⌫ 01 = ͑0,2 ͒ and ⌫ 10 = ͑2 ,0͒ while the circular band is strongest at ⌫ 11 = ͑2 ,2 ͒.…”

“…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.…”