Oxygen vacancies at titanate interfaces: Two-dimensional magnetism and orbital reconstruction

Pavlenko, N. V.; Kopp, Thilo; Tsymbal, Evgeny Y.; Mannhart, J.; Sawatzky, G. A.

doi:10.1103/physrevb.86.064431

Cited by 138 publications

(154 citation statements)

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“…The local moments themselves are postulated to arise either from electronic correlations 36 or interfacial disorders 32,34 , or are related to oxygen vacancies 31,37 . Extrinsic sources of magnetic impurities have been ruled out experimentally 11,12,15 .…”

Section: Discussionmentioning

confidence: 99%

Room-temperature electronically-controlled ferromagnetism at the LaAlO3/SrTiO3 interface

et al. 2014

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Reports of emergent conductivity, superconductivity and magnetism have helped to fuel intense interest in the rich physics and technological potential of complex-oxide interfaces. Here we employ magnetic force microscopy to search for room-temperature magnetism in the well-studied LaAlO 3 /SrTiO 3 system. Using electrical top gating to control the electron density at the oxide interface, we directly observe the emergence of an in-plane ferromagnetic phase as electrons are depleted from the interface. Itinerant electrons that are reintroduced into the interface align antiferromagnetically with the magnetization at first screening and then destabilizing it as the conductive regime is approached. Repeated cycling of the gate voltage results in new, uncorrelated magnetic patterns. This newfound control over emergent magnetism at the interface between two non-magnetic oxides portends a number of important technological applications.

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Section: Discussionmentioning

confidence: 99%

Room-temperature electronically-controlled ferromagnetism at the LaAlO3/SrTiO3 interface

et al. 2014

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“…In the case of SrTiO 3 -based heterostructures, where ferromagnetism has been previously reported [7][8][9], recent X-ray magnetic circular dichroism experiments found it to arise from d xy orbitals of Ti 3+ character [27], and to be quenched by annealing in oxygen, suggesting a decisive role of oxygen vacancies in this phenomenon [28]. Interestingly, the-7 oretical calculations have found that clusters of oxygen vacancies could induce an orbital reconstruction, generating an interfacial magnetic state with a dominant contribution from the d xy states to the magnetic moment and an exchange energy splitting as large as a fraction of eV [29,30]. Alternative models, based the interfacial splitting of t 2g orbital degeneracy in combination with electron correlations, have also been proposed [2,[31][32][33][34].…”

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confidence: 99%

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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“…[18][19][20][21][22][23][24][25][26][27] Under certain conditions, it is energetically favorable for oxygen atoms near the interface to diffuse out of the STO during the initial stages of growth, stabilizing a confined conducting layer. [18][19][20][21][22][23][24][25][26][27]31,32 Since this metallic layer results from the formation of oxygen vacancies near the interface, it characteristically vanishes with oxygen atmospheric annealing. [23][24][25][26][27] One such heterostructure is alumina/STO.…”

Section: Introductionmentioning

confidence: 99%

Quasi-two-dimensional electron gas at the epitaxial alumina/SrTiO3 interface: Control of oxygen vacancies

Kormondy

Posadas

Ngo

et al. 2015

Journal of Applied Physics

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In this paper, we report on the highly conductive layer formed at the crystalline γ-alumina/SrTiO3 interface, which is attributed to oxygen vacancies. We describe the structure of thin γ-alumina layers deposited by molecular beam epitaxy on SrTiO3 (001) at growth temperatures in the range of 400–800 °C, as determined by reflection-high-energy electron diffraction, x-ray diffraction, and high-resolution electron microscopy. In situ x-ray photoelectron spectroscopy was used to confirm the presence of the oxygen-deficient layer. Electrical characterization indicates sheet carrier densities of ∼1013 cm−2 at room temperature for the sample deposited at 700 °C, with a maximum electron Hall mobility of 3100 cm2V−1s−1 at 3.2 K and room temperature mobility of 22 cm2V−1s−1. Annealing in oxygen is found to reduce the carrier density and turn a conductive sample into an insulator.

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Oxygen vacancies at titanate interfaces: Two-dimensional magnetism and orbital reconstruction

Cited by 138 publications

References 56 publications

Room-temperature electronically-controlled ferromagnetism at the LaAlO3/SrTiO3 interface

Room-temperature electronically-controlled ferromagnetism at the LaAlO3/SrTiO3 interface

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

Quasi-two-dimensional electron gas at the epitaxial alumina/SrTiO3 interface: Control of oxygen vacancies

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