Spin–Charge Interconversion in KTaO<sub>3</sub> 2D Electron Gases

Vicente-Arche, Luis M.; Bréhin, Julien; Varotto, Sara; Cosset‐Chéneau, Maxen; Mallik, Srijani; Salazar, Raphaël; Noël, Paul; Vaz, Diogo C.; Trier, Felix; Bhattacharya, S.; Sander, Anke; Fèvre, P. Le; Bertran, F.; Saiz, G.; Ménard, Gerbold; Bergeal, N.; Barthélémy, A.; Li, Hai; Lin, Chia‐Ching; Nikonov, Dmitri E.; Young, Ian A.; Rault, Julien; Vila, Laurent; Attané, Jean-Philippe; Bibès, Manuel

doi:10.1002/adma.202102102

Cited by 37 publications

(50 citation statements)

References 44 publications

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“…For the AlO x /KTaO 3 heterointerface, two species of carriers appears when the total carrier density increases to around 4.5 × 10 13 cm –2 . [ 53 ] Interestingly, in this experiment, the maximum of Rashba SOC strength is also achieved at n s ≈ 4.5 × 10 13 cm –2 . Therefore, we also expect a Lifshitz transition as the carrier density increase to 4.5 × 10 13 cm –2 .…”

Section: Resultsmentioning

confidence: 54%

“…The maximum α is ≈ 7.93 × 10 –12 eV m, while the maximum Δ is ≈ 24.96 meV. For the AlO x /KTO heterostructure, the strength of the Rashba SOC α is at the range of 7 × 10 –12 to 28 × 10 –12 eV m. [ 53 ] The α in this experiment is within this range. This spin split energy is comparable to that of the amorphous‐LAO/KTO heterostructure, [ 24 ] but larger than that of STO‐based 2DEG as expected.…”

Section: Resultsmentioning

confidence: 63%

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Large Optical Tunability of 5d 2D Electron Gas at the Spinel/Perovskite γ‐Al₂O₃/KTaO₃ Heterointerface

Zhang

et al. 2022

Adv Materials Inter

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from the Ti 3d t 2g electrons. Apart from STO, 5d perovskite oxide KTaO 3 (KTO) can also host 2DEG. [19] These 5d 2DEG can be achieved by the Ar + ions irradiating of KTO surface [20] and growing the LaTiO 3 , LAO, or EuO overlayers on top of KTO. [21][22][23] Compared to the 3d STObased 2DEG, the 5d 2DEG exhibit even more remarkable properties. For example, the 2DEG at the interface of LAO/KTO heterostructure exhibits 2D superconductivity with a higher transition temperature, [22] and the 2D magnetic order with high Curie temperature appears at the EuO/KTaO 3 heterointerface. [23] More importantly, different from STO 2DEG, 5d 2DEG expects a stronger spin-orbit coupling. In analogy to LAO/STO, Zhang et al. [24,25] synthesized LAO/KTO heterostructures and discovered high mobility 2DEGs at the interface. They also found that the Rashba effect of the 5d 2DEG can be tuned by back gate voltage and light illumination. However, the LAO overlayer is often found to be amorphous when grown on KTO regardless the deposition temperatures and oxygen pressures during the film growth.For LAO/STO-related heterostructures, it has been discovered that Al-rich capping layer is crucial to ensure a conducting interface. [26,27] Notably, different from perovskite-type conducting oxide interfaces, Chen et al. [28][29][30] prepared the γ-Al 2 O 3 (GAO) film with spinel structure on the STO substrate. A relatively low crystalline temperature (down to room temperature) for GAO is also observed in GAO/STO. [29] The non-isostructural spinel/perovskite interface exists a metallic 2DEG with carrier mobility as high as 100 000 cm 2 V -1 s -1 at 2 K. In contrast to perovskite LAO which shows a large lattice mismatch with KTO (around 4.8%), GAO with spinel structure is a binary insulating metal oxide with bandgap of 8.7 eV, and the lattice constant is a GAO = 0.7911 nm. [31][32][33] This lattice constant matches well with twice of KTO lattice constant (a KTO = 0.3989 nm). Remarkably, such non-isostructural 5d heterostructures of GAO/KTO has never been studied to date. In this letter, we have grown successfully, the epitaxial GAO/KTO heterostructure at different deposition temperatures, and obtained high mobility interfacial 2DEGs with different carrier densities. Furthermore, the carrier density and Rashba spin-orbit coupling (SOC) of the 2DEG are found to be tuned strongly by the laser light. The maximum change of the carrier density is 3 × 10 13 cm -2 , among the largest tunability of complex oxide heterostructures.The 5d 2D electron gas (2DEG) in KTaO 3 -based heterostructures exhibits stronger spin-orbit coupling and higher superconducting transition temperature compared to the 3d SrTiO 3 -based 2DEG, thus attracts much attention recently. However, compared to the intensively investigated isostructural perovskite-type interfaces, the non-isostructural 5d oxide interfaces remain less investigated. Herein, for the first-time, epitaxial spinel/perovskite γ-Al 2 O 3 /KTaO 3 heterointerface is created, at a deposition temperature as low as 300 °C....

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Section: Resultsmentioning

confidence: 54%

Section: Resultsmentioning

confidence: 63%

Large Optical Tunability of 5d 2D Electron Gas at the Spinel/Perovskite γ‐Al₂O₃/KTaO₃ Heterointerface

Zhang

et al. 2022

Adv Materials Inter

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“…The induced torque is sensitive to the interface crystallinity, and one can realize different experimental setups to capture the angular dependency on the torque. We remark that (111) KaTiO

-based heterostructures [ 28 , 44 , 45 ] have a similar crystalline structure with higher SOC, which could enhance the EE and OEE. Therefore, they could be an interesting system to further apply our analysis.…”

Section: Discussionmentioning

confidence: 99%

Tunable Spin and Orbital Edelstein Effect at (111) LaAlO3/SrTiO3 Interface

et al. 2022

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Converting charge current into spin current is one of the main mechanisms exploited in spintronics. One prominent example is the Edelstein effect, namely, the generation of a magnetization in response to an external electric field, which can be realized in systems with lack of inversion symmetry. If a system has electrons with an orbital angular momentum character, an orbital magnetization can be generated by the applied electric field, giving rise to the so-called orbital Edelstein effect. Oxide heterostructures are the ideal platform for these effects due to the strong spin–orbit coupling and the lack of inversion symmetries. Beyond a gate-tunable spin Edelstein effect, we predict an orbital Edelstein effect an order of magnitude larger then the spin one at the (111) LaAlO3/SrTiO3 interface for very low and high fillings. We model the material as a bilayer of t2g orbitals using a tight-binding approach, whereas transport properties are obtained in the Boltzmann approach. We give an effective model at low filling, which explains the non-trivial behaviour of the Edelstein response, showing that the hybridization between the electronic bands crucially impacts the Edelstein susceptibility.

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“…Experiments under ultrahigh vacuum conditions on cleaved single crystals verified the formation of a metallic q2DES in the uppermost lattice layers of the (001) and (111) surfaces of KTO [17][18][19]. Recently, intriguing properties of this q2DES like superconductivity and the Edelstein effect have been demonstrated [20][21][22]. Most likely induced through n-doping resulting from the formation of oxygen vacancies (V O ) [17] at the surfaces, these q2DESs quickly decay when the crystals are exposed to air.…”

Section: Introductionmentioning

confidence: 93%

Hard x-ray angle-resolved photoemission from a buried high-mobility electron system

Zapf¹,

Schmitt²,

Gabel³

et al. 2021

Preprint

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Novel two-dimensional electron systems at the interfaces and surfaces of transition-metal oxides recently have attracted much attention as they display tunable, intriguing properties that can be exploited in future electronic devices. Here we show that a high-mobility quasi-two-dimensional electron system with strong spin-orbit coupling can be induced at the surface of a KTaO3 (001) crystal by pulsed laser deposition of a disordered LaAlO3 film. The momentum-resolved electronic structure of the buried electron system is mapped out by hard X-ray angle-resolved photoelectron spectroscopy. From a comparison to calculations it is found that the band structure deviates from that of electron-doped bulk KTaO3 due to the confinement to the interface. Nevertheless, the Fermi surface appears to be clearly three-dimensional. From the k-broadening of the Fermi surface and core-level depth profiling we estimate the extension of the electron system to be at least 1 nm but not much larger than 2 nm, respectively.

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Spin–Charge Interconversion in KTaO₃ 2D Electron Gases

Cited by 37 publications

References 44 publications

Large Optical Tunability of 5d 2D Electron Gas at the Spinel/Perovskite γ‐Al₂O₃/KTaO₃ Heterointerface

Large Optical Tunability of 5d 2D Electron Gas at the Spinel/Perovskite γ‐Al₂O₃/KTaO₃ Heterointerface

Tunable Spin and Orbital Edelstein Effect at (111) LaAlO3/SrTiO3 Interface

Hard x-ray angle-resolved photoemission from a buried high-mobility electron system

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Spin–Charge Interconversion in KTaO3 2D Electron Gases

Cited by 37 publications

References 44 publications

Large Optical Tunability of 5d 2D Electron Gas at the Spinel/Perovskite γ‐Al2O3/KTaO3 Heterointerface

Large Optical Tunability of 5d 2D Electron Gas at the Spinel/Perovskite γ‐Al2O3/KTaO3 Heterointerface

Tunable Spin and Orbital Edelstein Effect at (111) LaAlO3/SrTiO3 Interface

Hard x-ray angle-resolved photoemission from a buried high-mobility electron system

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Spin–Charge Interconversion in KTaO₃ 2D Electron Gases

Large Optical Tunability of 5d 2D Electron Gas at the Spinel/Perovskite γ‐Al₂O₃/KTaO₃ Heterointerface

Large Optical Tunability of 5d 2D Electron Gas at the Spinel/Perovskite γ‐Al₂O₃/KTaO₃ Heterointerface