Momentum-resolved electronic structure at a buried interface from soft X-ray standing-wave angle-resolved photoemission

Gray, A. X.; Minář, J.; Pluciński, Ł.; Huijben, Mark; Bostwick, Aaron; Rotenberg, Eli; Yang, See‐Hun; Braun, J.; Winkelmann, Aimo; Conti, G.; Eiteneer, D.; Rattanachata, Arunothai; Greer, A. A.; Ciston, Jim; Ophus, Colin; Rijnders, Guus; Blank, Dave H.A.; Doennig, David; Kortright, Jeffrey B.; Schneider, Claus M.; Ebert, H.; Fadley, C. S.

doi:10.1209/0295-5075/104/17004

Cited by 39 publications

(59 citation statements)

References 42 publications

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“…This degree of agreement further confirms the accuracy of the resonant optical constants and the validity of the structure we are assuming for the sample. It also further demonstrates our previously established SW calculation methodology [32,33,35]. The RCs of Sr 3d and Gd 4f (as well as Gd 4d, not shown here) again strongly differ, with maxima and minima out of phase, a direct consequence of their origin from different layers of the sample.…”

Section: Sw Core-level Photoemission and Arpessupporting

confidence: 79%

“…or 19.8Å thick). The period of the multilayer is thus 35.5Å, which will also be the period of the SW perpendicular to the surface of the sample [32,33]. The STO and GTO layers were coherently and compressively strained to the underlying LSAT by about 1%.…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Such scans generate rocking curves (RCs) of core and valence photoelectron intensities that encompass all the elements in the sample. Additional interference effects due to reflection of the x-rays from the top and bottom of the multilayer sample generate fine structure termed "Kiessig fringes" [32,33]. If the multilayer sample has a total thickness of D ML = Nd ML , where N is the number of bilayer repeats in the multilayer mirror, the interference maxima will appear for mλ x = 2D ML sin θ Kiessig,m , where m is some high order of interference and θ Kiessig,m is the incidence angle corresponding to this order.…”

Section: -2mentioning

confidence: 99%

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Energetic, spatial, and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides

Nemšák¹,

Conti²,

Gray³

et al. 2016

Phys. Rev. B

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The interfaces between two condensed phases often exhibit emergent physical properties that can lead to new physics and novel device applications and are the subject of intense study in many disciplines. We here apply experimental and theoretical techniques to the characterization of one such interesting interface system: the two-dimensional electron gas (2DEG) formed in multilayers consisting of SrTiO 3 (STO) and GdTiO 3 (GTO). This system has been the subject of multiple studies recently and shown to exhibit very high carrier charge densities and ferromagnetic effects, among other intriguing properties. We have studied a 2DEG-forming multilayer of the form [6 unit cells (u.c.) STO/3 u.c. of GTO] 20 using a unique array of photoemission techniques including soft and hard x-ray excitation, soft x-ray angle-resolved photoemission, core-level spectroscopy, resonant excitation, and standing-wave effects, as well as theoretical calculations of the electronic structure at several levels and of the actual photoemission process. Standing-wave measurements below and above a strong resonance have been exploited as a powerful method for studying the 2DEG depth distribution. We have thus characterized the spatial and momentum properties of this 2DEG in detail, determining via depth-distribution measurements that it is spread throughout the 6 u.c. layer of STO and measuring the momentum dispersion of its states. The experimental results are supported in several ways by theory, leading to a much more complete picture of the nature of this 2DEG and suggesting that oxygen vacancies are not the origin of it. Similar multitechnique photoemission studies of such states at buried interfaces, combined with comparable theory, will be a very fruitful future approach for exploring and modifying the fascinating world of buried-interface physics and chemistry.

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Section: Sw Core-level Photoemission and Arpessupporting

confidence: 79%

Section: Experimental Methodsmentioning

confidence: 99%

Section: -2mentioning

confidence: 99%

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Energetic, spatial, and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides

Nemšák¹,

Conti²,

Gray³

et al. 2016

Phys. Rev. B

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“…Recently developed experimental techniques exist to probe buried LSMO/STO interfaces for the presence of the interfacespecific features predicted by our calculations to originate from the polar mismatch. 31,32 Furthermore, the band alignment between LSMO and STO can be continuously controlled by sub-unit-cell deposition of a SrMnO 3 layer, 33 which in our case allows a shift of the Fermi energy and thus control of the magnitude of the TAMR effect (Fig. 5).…”

Section: Outlook and Conclusionmentioning

confidence: 86%

Tunneling anisotropic magnetoresistance in a magnetic tunnel junction with half-metallic electrodes

Burton

Tsymbal

2016

Phys. Rev. B

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Tunneling anisotropic magnetoresistance (TAMR) is the difference in resistance of a magnetic tunnel junction due to a change in magnetization direction of one or both magnetic electrodes with respect to the flow of current. We present results of first-principles density functional calculations of the TAMR effect in magnetic tunnel junctions with La 0.7 Sr 0.3 MnO 3 (LSMO) electrodes and a SrTiO 3 (STO) tunneling barrier. We find ~500% difference in resistance between magnetization in the plane and out of the plane. This large TAMR effect originates from the half-metallic nature of LSMO: when magnetization is out-of-plane spin-orbit coupling (SOC) contributions to the transmission comes only from spin-flip scattering, which is intrinsically small due to the half-metallicity. For in-plane magnetization, however, there is a large non-spin-flip SOC contribution to the conductance. The large magnitude of the effect stems from the additional fact that there is an inherent polar discontinuity between LSMO and STO which leads to quasi-localized states at the interface whose influence on tunneling is strongly dependent on the magnetization orientation.

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“…As a future suggestion, the analysis of angle-resolved photoemission (ARPES) in NTR-HAXPES, should provide direct access to the depth-resolved interface band structure, as demonstrated recently in soft x-ray standing-wave ARPES 42 . …”

mentioning

confidence: 89%

Depth Profiling Charge Accumulation from a Ferroelectric into a Doped Mott Insulator

et al. 2015

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The electric field control of functional properties is a crucial goal in oxide-based electronics.Non-volatile switching between different resistivity or magnetic states in an oxide channel can be achieved through charge accumulation or depletion from an adjacent ferroelectric. However, the way in which charge distributes near the interface between the ferroelectric and the oxide remains poorly known, which limits our understanding of such switching effects.Here we use a first-of-a-kind combination of scanning transmission electron microscopy with electron energy loss spectroscopy, near-total-reflection hard X-ray photoemission spectroscopy, and ab-initio theory to address this issue. We achieve a direct, quantitative, atomic-scale characterization of the polarization-induced charge density changes at the interface between the ferroelectric BiFeO3 and the doped Mott insulator Ca1-xCexMnO3, thus providing insight on how interface-engineering can enhance these switching effects. 3The ferroelectric control of functional properties in strongly correlated oxide nanostructures through electrostatic carrier density modulations has inspired intensive research efforts 1,2 .The field effect technique is particularly attractive for nanostructures consisting of complex oxides such as mixed-valence manganites, as these electron-correlated systems exhibit rich phase diagrams 3 .Hole-doped mixed-valence manganites with predominant Mn 3+ oxidation state have been extensively investigated [3][4][5][6][7][8] . In particular, recent works have been devoted on the interface between the half-metal La1-xSrxMnO3 (LSMO) manganite and ferroelectrics such as Pb(ZrxTi1- In these recent reports 13,14 , the resistivity change in the manganite channel induced by polarization switching in the ferroelectric BiFeO3 was limited to one order of magnitude while changes of several orders were reported for thin films of CaMnO3 tuned by different doping levels, strains or by electrolyte gating 12 . Typical electron injection of around 0.1 free electrons in the manganite channel were estimated by Hall measurements and associated with this resistivity change.A charge distribution measurement on a unit cell scale at the Ca manganite/ferroelectric interface is thus required to understand, control and possibly enhance the magnitude of the resistivity switching effects. In the present study, a first-of-a-kind combination of scanning transmission electron microscopy (STEM) coupled to electron energy loss spectroscopy (EELS) [15][16][17][18] , and grazing-incidence hard x-ray photoemission spectroscopy (HAXPES) in a near-total-reflection (NTR) condition have been used as site-sensitive valence probes to address the electronic and structural properties of BiFeO3 and Ca1-xCexMnO3 heterostructures (x=0, 2, 4 at.% nominal Ce concentrations) at the atomic scale. Our experimental results have also been compared to local density functional theory (DFT).We have used these two novel and complementary methods to evaluate electron densities in manganite oxides. ...

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Momentum-resolved electronic structure at a buried interface from soft X-ray standing-wave angle-resolved photoemission

Cited by 39 publications

References 42 publications

Energetic, spatial, and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides

Energetic, spatial, and momentum character of the electronic structure at a buried interface: The two-dimensional electron gas between two metal oxides

Tunneling anisotropic magnetoresistance in a magnetic tunnel junction with half-metallic electrodes

Depth Profiling Charge Accumulation from a Ferroelectric into a Doped Mott Insulator

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