Ferroelectric relaxation of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mi mathvariant="normal">SrTiO</mml:mi></mml:mrow><mml:mrow><mml:mn>3</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>(100) surface

Bickel, N.; Schmidt, G.; Heinz, K.; Müller, K.

doi:10.1103/physrevlett.62.2009

Cited by 258 publications

(184 citation statements)

References 11 publications

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“…In the case of SrTiO 3 , on the other hand, the bulk material is merely a transparent paramagnetic band insulator at all temperatures, while the 2DEG at its surface shows both a non-trivial helical spin texture and magnetism. These original spin-polarized states must then clearly arise from intrinsic properties of the 2DEG and the spatial region where it is confined.Thus, in analogy with the case of magnetism in SrTiO 3 -based heterostructures, we speculate that for the 2DEG at the bare SrTiO 3 surface not only the surface-induced translationalsymmetry breaking and subband orbital ordering [12], but also oxygen vacancies [12,13], and possibly lattice distortions [37] and/or electron exchange correlations, may play a fundamental role in establishing the observed non-trivial magnetic ground state. The exploration of all these possibilities, and the microscopic explanation of our observations, are at this point open issues beyond the scope of this work, and should be the subject of future theoretical and experimental research.…”

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confidence: 60%

Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

et al. 2014

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1 Two-dimensional electron gases (2DEGs) forming at the interfaces of transition metal oxides [1][2][3] display a range of properties including tunable insulatorsuperconductor-metal transitions [4][5][6], large magnetoresistance [7], coexisting ferromagnetism and superconductivity [8, 9], and a spin splitting of a few meV [10,11]. Strontium titanate (SrTiO 3 ), the cornerstone of such oxide-based electronics, is a transparent, nonmagnetic, wide-band-gap insulator in the bulk, and has recently been found to host a surface 2DEG [12][13][14][15]. The most strongly confined carriers within this 2DEG comprise two sub-bands, separated by an energy gap of 90 meV and forming concentric circular Fermi surfaces [12,13,15].Using spin-and angle-resolved photoemission spectroscopy (SARPES), we show that the electron spins in these sub-bands have opposite chiralities. Although the Rashba effect might be expected to give rise to such spin textures, the giant splitting of almost 100 meV at the Fermi level is far larger than anticipated [16,17].Moreover, in contrast to a simple Rashba system, the spin-polarized sub-bands are non-degenerate at the Brillouin zone centre. This degeneracy can be lifted by time-reversal symmetry breaking, implying the possible existence of magnetic order. These results show that confined electronic states at oxide surfaces can be endowed with novel, non-trivial properties that are both theoretically challenging to anticipate and promising for technological applications.The 2DEG at the surface of SrTiO 3 , formed by confined electrons of the t 2g conduction band with Ti-3d character, is universal in the sense that its constituent subbands, their fillings, and their Fermi surfaces are independent of the bulk sample doping and of whether the surfaces are prepared by cleaving [12,13] or by etching and in situ annealing [15]. This 2DEG consists on two light electron subbands dispersing down to about −180 meV and, respectively, −90 meV below the Fermi level (E F ), producing concentric Fermi surfaces around the Brillouin zone center, and heavy shallow subbands dispersing down to about −40 meV, forming ellipsoidal Fermi surfaces [12,13,15].In fact, the 2DEG in SrTiO 3 has been associated with a band-bending of ∼ 300 meV at the surface of the material [12,13,15]. In such a quantum well profile, the most bound light subbands are tightly confined near the surface, while the less bound heavy subbands are more delocalized towards the bulk [12,15]. The present work focuses on resolving the spin 2 structure of the strongly two-dimensional light subbands, which are the most technologically relevant in terms of their carrier concentration and mobility.The surface band-bending of ∼ 300 meV amounts to an electric field F ∼ 100 MV/m confining the conduction electrons near the surface. In a simple approximation, this field will induce a so-called "Rashba splitting" of the spin states in each subband, with the largest splitting occurring for the most bound subbands. In an ideal surface, the corresponding momentum separat...

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Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

et al. 2014

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“…4a, we obtain 18 nC/cm 2 as an estimate of the remnant polarization for a maximum applied voltage of 0.8 V. Given that ferroelectric behavior in LaAlO 3 has never been observed and that the SrTiO 3 is an incipient ferroelectric, any dipole switching can be attributed to a thin layer in SrTiO 3 near the interface. 38 Although, we do note that recent theoretical models of the LaAlO 3 /SrTiO 3 system point to the possibility of ferroelectric-like distortions in the LaAlO 3 layer as well. 2,39,40 In accord with previous observations however, 38 we suspect an interface dipole in SrTiO 3 , which in turn suggests that the electron gas lies not exactly at the interface, but burried one or a few monolayers within the SrTiO 3 .…”

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confidence: 99%

“…38 Although, we do note that recent theoretical models of the LaAlO 3 /SrTiO 3 system point to the possibility of ferroelectric-like distortions in the LaAlO 3 layer as well. 2,39,40 In accord with previous observations however, 38 we suspect an interface dipole in SrTiO 3 , which in turn suggests that the electron gas lies not exactly at the interface, but burried one or a few monolayers within the SrTiO 3 . We thus speculate that the large influx of charge carriers into the potential well at the onset of Zener tunneling changes the local electric field and modifies the dipole strength, causing the observed hysteretic behaviour in CV .…”

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confidence: 99%

Built-in and induced polarization across LaAlO3/SrTiO3 heterojunctions

et al. 2010

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Ionic crystals terminated at oppositely charged polar surfaces are inherently unstable and expected to undergo surface reconstructions to maintain electrostatic stability. Essentially, an electric field that arises between oppositely charged atomic planes gives rise to a built-in potential that diverges with thickness. Here we present evidence of such a built-in potential across polar LaAlO3 thin films grown on SrTiO3 substrates, a system well known for the electron gas that forms at the interface. By performing tunneling measurements between the electron gas and metallic electrodes on LaAlO3 we measure a built-in electric field across LaAlO3 of 80.1 meV/Å. Additionally, capacitance measurements reveal the presence of an induced dipole moment across the heterostructure. We forsee use of the ionic built-in potential as an additional tuning parameter in both existing and novel device architectures, especially as atomic control of oxide interfaces gains widespread momentum.As dictated by Maxwell's equations, the accumulation of screening charges at the boundary between dissimilar materials is one means 1 of ensuring a continuous electric displacement at the interface. 2 For instance, a layer of trapped screening charge forms the two dimensional electron gas that compensates a polarization mismatch at gallium nitride 3 and zinc oxide 4 based heterostructure interfaces. In insulating oxides, charge accumulation was observed at the interface between SrTiO 3 substrates with atomically precise surfaces and polar LaAlO 3 films. 5 LaAlO 3 thin films grown on singly terminated SrTiO 3 surfaces 6 comprise negatively charged AlO 2 and positively charged LaO end planes and are polar in the ionic limit. 1,7,8 When at least four unit cells (u.c.) of LaAlO 3 are deposited on TiO 2 terminated SrTiO 3 , an electron gas forms near the interface in SrTiO 3 . 5,9,10 It is often hypothesized that at a thickness of four u.c. the potential across LaAlO 3 exceeds the band gap of SrTiO 3 and electrons tunnel from the valence band of LaAlO 3 to the SrTiO 3 potential well, completely diminishing the potential across LaAlO 3 . 11 Thus within this picture, in the presence of an electron gas no field would be expected across the LaAlO 3 . However, if all the charge carriers do not lie precisely at the interface or have an extrinsic (oxygen vacancies 12 or cation doping 13 ) origin, the LaAlO 3 potential will not be fully screened and can thus be probed. 14 Alternatively, the precise band alignment between the LaAlO 3 and SrTiO 3 will also determine the strength of the residual fields in the LaAlO 3 . 15 Addressing this issue by determining the existence of an uncompensated built-in potential in LaAlO 3 is central to understanding the true nature of the polar LaAlO 3 /SrTiO 3 interface.We probe the potential landscape across the LaAlO 3 and the interface region in SrTiO 3 by employing a typical metal-insulator-metal capacitor geometry such that the LaAlO 3 thin films form the dielectric layer sandwiched between evaporated metallic electrodes an...

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“…17,19,20 Theoretical calculations using several techniques have led to band gaps of SrTiO 3 in the ranges 1.71 to 2.2 eV for LDA and GGA, 6, 10, 12 1.87 to 3.63 eV for Hybrid DFT, 5,9,10 and value as high as 11.97 eV for the Hatree-Fock (HF) method. 10 In this paper, we present a simple, yet robust, and ab-initio method, based on self consistent solutions of the pertinent system of equations, [51][52][53][54] that correctly predicts band gap values and related electronic properties of SrTiO 3 rigorously, from first principle, within the LCAO-GGA formalism.…”

Section: Introductionmentioning

confidence: 99%

“…SrTiO 3 has found usage in optical switches, grain-boundary barrier layer capacitors, catalytic activators, waveguides, laser frequency doubling, high capacity computer memory cells, oxygen gas sensors, semiconductivity, etc. [9][10][11][12][13][14][15][16] During the last few decades, the electronic, structural, elastic, and optical properties of SrTiO 3 (STO), as a model of ABO 3 perovskite, have been under intensive investigation both experimentally [17][18][19][20][21][22][23] and theoretically. [9][10][11][12][13][24][25][26][27] But, from a theoretical point of view, a proper description of its electronic properties is still an area of active research.…”

Section: Introductionmentioning

confidence: 99%

First principle electronic, structural, elastic, and optical properties of strontium titanate

et al. 2012

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We report self-consistent ab-initio electronic, structural, elastic, and optical properties of cubic SrTiO3 perovskite. Our non-relativistic calculations employed a generalized gradient approximation (GGA) potential and the linear combination of atomic orbitals (LCAO) formalism. The distinctive feature of our computations stem from solving self-consistently the system of equations describing the GGA, using the Bagayoko-Zhao-Williams (BZW) method. Our results are in agreement with experimental ones where the later are available. In particular, our theoretical, indirect band gap of 3.24 eV, at the experimental lattice constant of 3.91 Å, is in excellent agreement with experiment. Our predicted, equilibrium lattice constant is 3.92 Å, with a corresponding indirect band gap of 3.21 eV and bulk modulus of 183 GPa

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Ferroelectric relaxation of theSrTiO3(100) surface

Cited by 258 publications

References 11 publications

Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

Giant spin splitting of the two-dimensional electron gas at the surface of SrTiO3

Built-in and induced polarization across LaAlO3/SrTiO3 heterojunctions

First principle electronic, structural, elastic, and optical properties of strontium titanate

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