Two-dimensional electron gas at the (001) surface of ferromagnetic EuTiO3

Giant spin-dependent Seebeck effect from fully spin-polarized carriers in n-doped EuTiO3: a prototype material for spin-caloritronic applications

“…We obtain an indirect band gap of 1.51 eV between the Eu 4f VBT at the R point and the Ti 3d CBB at the Γ point, slightly larger than the direct band gap at Γ . We found the centroid of the Eu 4f states located at a bonding energy ∼1.8 eV, in good agreement with the 2 eV peak found by ARPES 37 and XPS. 52…”

“…The gap region displays three well distinct band groups: the Ti 3d t 2g states at the conduction band bottom (CBB), the fully spin-polarized Eu 4f states with a nominal magnetization of 7 m B /Eu at the valence band top (VBT), and the O 2p states which mainly contribute to the valence bands. We obtain an indirect band gap of 1.51 eV between the Eu 4f VBT at the R point and the Ti 3d CBB at the G point, slightly larger than the direct band gap at G. We found the centroid of the Eu 4f states located at a bonding energy ∼1.8 eV, in good agreement with the 2 eV peak found by ARPES 37 and XPS. 52 In experiments, the 4f peak displays a ∼2 eV spectral width which is much larger than the calculated ∼0.5 eV bandwidth.…”

“…We assume U = 7.5 eV and 4.0 eV for Eu 4f and Ti 3d states, respectively: previous studies showed that these values deliver a calculated band structure for ETO in nice agreement with photoemission measurements. 36,37…”

“…The structural similarity makes ETO perfectly suited to be epitaxially grown on STO substrates and integrable in oxide heterostructures. 37,[46][47][48][49] Unlike STO, ETO features a large intrinsic magnetization embodied in the fully spin-polarized Eu 4f states; Owing to the strong 4f orbital localization, the pristine material is a paramagnetic semiconductor at room-T, and becomes antiferromagnetic (AFM) below T N = 5.2 K; this long-range order is imputed to the Eu 4f-Ti 3d orbital coupling, as described by a number of experimental and theoretical investigations. [50][51][52][53] Also similarly to STO, ETO displays huge electric permittivity (∼160 at room-T), which undergoes large changes upon application of a magnetic eld.…”

Ultra-thin magnetic film with giant phonon-drag for heat to spin current conversion

“…[17][18][19][20][21] Pristine ETO is antiferromagnetic with T N = 5.5 K, 2 but ferromagnetism (FM) with T c B 8-9 K can be introduced by a variety of n-doping substitutions. 20,[22][23][24][25][26] Consistent with these findings, FM order is also reported for the 2DEG present at the ETO (100) surface 27 and, most crucially for our purposes, at the STO/ETO/LAO interface, [28][29][30][31] where ferromagnetism up to T B 8 K is observed. 28,29 A remarkable aspect reported for n-doped ETO is that carrier concentration is characterized by a large spin-polarization fraction, nearing 100% at low n. 21,32 Our working hypothesis is that similar characteristics are displayed in 2D form by the STO/ETO/LAO heterostructure as well.…”