Engineering two-dimensional superconductivity and Rashba spin–orbit coupling in LaAlO3/SrTiO3 quantum wells by selective orbital occupancy

Herranz, G.; Singh, Gyanendra; Bergeal, N.; Jouan, A.; Lesueur, J.; Gàzquez, Jaume; Varela, M.; Scigaj, Mateusz; Dix, N.; Sánchez, F.; Fontcuberta, J.

doi:10.1038/ncomms7028

Cited by 168 publications

(202 citation statements)

References 53 publications

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“…The above scenario is also consistent with measurements of superconductivity in [110] oriented LAO/STO samples for which the orbital ordering is different from that of the [001] orientation. 66 In this case, T c does not disappear at low doping levels.…”

Section: Superconductivitymentioning

confidence: 95%

Research Update: Conductivity and beyond at the LaAlO3/SrTiO3 interface

2016

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In this review, we focus on the celebrated interface between two band insulators, LaAlO3 and SrTiO3, that was found to be conducting, superconducting, and to display a strong spin-orbit coupling. We discuss the formation of the 2-dimensional electron liquid at this interface, the particular electronic structure linked to the carrier confinement, the transport properties, and the signatures of magnetism. We then highlight distinctive characteristics of the superconducting regime, such as the electric field effect control of the carrier density, the unique tunability observed in this system, and the role of the electronic subband structure. Finally we compare the behavior of Tc versus 2D doping with the dome-like behavior of the 3D bulk superconductivity observed in doped SrTiO3. This comparison reveals surprising differences when the Tc behavior is analyzed in terms of the 3D carrier density for the interface and the bulk.

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Section: Superconductivitymentioning

confidence: 95%

Research Update: Conductivity and beyond at the LaAlO3/SrTiO3 interface

2016

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“…The high density of states associated with the flat band is also advantageous for thermoelectric applications (24) and affects superconducting properties (25). To exploit the flat-band physics as well as the anisotropic features of the (110) 2DEG, a tuning of the carrier density is needed.…”

mentioning

confidence: 99%

Anisotropic two-dimensional electron gas at SrTiO ₃ (110)

Wang

Zhong

Hao

et al. 2014

Proc. Natl. Acad. Sci. U.S.A.

110

129

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Two-dimensional electron gases (2DEGs) at oxide heterostructures are attracting considerable attention, as these might one day substitute conventional semiconductors at least for some functionalities. Here we present a minimal setup for such a 2DEG--the SrTiO 3 (110)-(4 × 1) surface, natively terminated with one monolayer of tetrahedrally coordinated titania. Oxygen vacancies induced by synchrotron radiation migrate underneath this overlayer; this leads to a confining potential and electron doping such that a 2DEG develops. Our angle-resolved photoemission spectroscopy and theoretical results show that confinement along (110) is strikingly different from the (001) crystal orientation. In particular, the quantized subbands show a surprising "semiheavy" band, in contrast with the analog in the bulk, and a high electronic anisotropy. This anisotropy and even the effective mass of the (110) 2DEG is tunable by doping, offering a high flexibility to engineer the properties of this system. oxide surface | electronic structure | quantum confinement | perovskite | ARPES T he 2D electron gas (2DEG) observed in oxide heterostructures such as LaAlO 3 /SrTiO 3 (1, 2) offers a possible alternative to conventional semiconductors, not only for electronics at the nanoscale (3) but also because of the possibility of spin-polarized (4) and superconducting (5, 6) currents. An even simpler setup is to create a 2DEG directly at SrTiO 3 . Recently this was achieved by irradiating a (001) surface (7, 8) with synchrotron radiation, albeit the origin of the resulting 2DEG is still under debate (7-9). This system has two major drawbacks: (i) surface oxygen vacancies are very reactive and (ii) the (001) surface has no unique surface termination, as TiO 2 and SrO terraces may develop, and the surface structure strongly depends on sample treatment and history (10).Here, we show that a 2DEG can also be induced at SrTiO 3 (110), which is stabilized and covered by a reconstructed overlayer. This overlayer automatically forms to compensate the intrinsic polarity of the system. A SrTiO 3 crystal can be viewed as a stack of alternating (SrTiO) 4+ and (O 2 ) 4− planes along the [110] orientation, resulting in a dipole moment that diverges with increasing crystal thickness (11). As is often true for polar surfaces, this is prevented by one of several compensation mechanisms (11). Specifically, the SrTiO 3 (110) surface spontaneously forms a (4 × 1) reconstruction upon various different sample treatments, including annealing in a tube furnace with flowing high-purity oxygen (12) and standard ultrahigh vacuum preparation procedures (13,14). The reconstruction consists of a 2D, tetrahedrally coordinated titania overlayer (Fig. 1A), which, with a nominal stoichiometry of (Ti 1.5 O 4 ) 2− , quenches the overall dipole moment (12, 15). Because the Ti atoms in the tetrahedral titania surface layer of the reconstruction are saturated by strong, directional bonds, the (4 × 1) surface is chemically quite inert (16). Results and DiscussionExposing the SrTiO 3 ...

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“…In addition, stress caused by lattice mismatch between FeSe and STO substrate is also thought to be responsible for TC enhancement 4 . To figure out the key role of substrate, STO(110) substrate is of great interest because it resembles STO(001) in high density subsurface oxygen vacancies [22][23][24] but distinguishes itself by a rectangular in-plane lattice 25,26 and the correspondingly different dielectric constants 27,28 . Here, we investigated molecular beam epitaxy (MBE) growth of 1-UC FeSe films on STO(110) substrates (referred as FeSe/STO(110) hereafter) and studied the superconducting properties by combined in-situ STS and ex-situ transport measurement.…”

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confidence: 99%

“…We can clearly see that as the magnetic field increases, the superconductivity transition region becomes broader and TC shifts to lower temperatures. For a 2D superconductor, its response to an external magnetic field normal to the 2D plane is expected to follow the linear Ginzburg-Landau formula 24 :…”

mentioning

confidence: 99%

Interface induced high temperature superconductivity in single unit-cell FeSe on SrTiO3(110)

Zhou

Zhang

Liu

et al. 2016

Applied Physics Letters

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We report high temperature superconductivity in one unit-cell (1-UC) FeSe films grown on SrTiO3 (STO) (110) substrate by molecular beam epitaxy. By in-situ scanning tunneling microscopy measurement, we observe a superconducting gap as large as 17 meV on the 1-UC FeSe films. Transport measurements on 1-UC FeSe/STO(110) capped with FeTe layers reveal superconductivity with an onset transition temperature (TC) of 31.6 K and an upper critical magnetic field of 30.2 T. We also find that TC can be further increased by external electric field although the effect is weaker than that on STO(001) substrate.

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Engineering two-dimensional superconductivity and Rashba spin–orbit coupling in LaAlO3/SrTiO3 quantum wells by selective orbital occupancy

Cited by 168 publications

References 53 publications

Research Update: Conductivity and beyond at the LaAlO3/SrTiO3 interface

Research Update: Conductivity and beyond at the LaAlO3/SrTiO3 interface

Anisotropic two-dimensional electron gas at SrTiO ₃ (110)

Interface induced high temperature superconductivity in single unit-cell FeSe on SrTiO3(110)

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Engineering two-dimensional superconductivity and Rashba spin–orbit coupling in LaAlO3/SrTiO3 quantum wells by selective orbital occupancy

Cited by 168 publications

References 53 publications

Research Update: Conductivity and beyond at the LaAlO3/SrTiO3 interface

Research Update: Conductivity and beyond at the LaAlO3/SrTiO3 interface

Anisotropic two-dimensional electron gas at SrTiO 3 (110)

Interface induced high temperature superconductivity in single unit-cell FeSe on SrTiO3(110)

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Anisotropic two-dimensional electron gas at SrTiO ₃ (110)