Tuning the Two-Dimensional Electron Liquid at Oxide Interfaces by Buffer-Layer-Engineered Redox Reactions

Chen, Yunzhong; Green, Robert J.; Sutarto, Ronny; He, Feizhou; Linderoth, Søren; Sawatzky, G. A.; Pryds, Nini

doi:10.1021/acs.nanolett.7b03744

Cited by 24 publications

(39 citation statements)

References 36 publications

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“…The perovskite structure is generally expressed as ABO 3-δ , where δ ≈ 0, A is the rare or alkaline earth metal and B is the transition metal. The oxygen deficiency converts the ideal cubic structure of ABO 3 into the orthogonal structure of ABO 2.5+δ' , where δ' is a small value that influences the space group of brownmillerites. 6 Therefore, brownmillerite can be regarded as oxygen-deficient perovskite.…”

Section: Introductionmentioning

confidence: 99%

Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective

Tao

Zhang

et al. 2019

J Am Ceram Soc

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Brownmillerite‐type oxides are a large family of structural and functional materials that are of great concern. In this study, the occupancy mechanism of Fe and Al ions in brownmillerite Ca2FeAlO5 is revealed and the specific configuration of Ca2FeAlO5 is proposed for the first time. Through the energy analysis of a series of conjectured models based on well‐defined ab initio calculations, we find that the distribution of Al and Fe in Ca2FeAlO5 follows the “homogeneous layer principle”, namely, Al and Fe tend to form homogeneous octahedral layers or tetrahedral chains rather than mixed layers or chains of two elements along the b axis. The theoretical Ca2FeAlO5 structure with specific atomic occupancy is proposed based on energy analysis and previous experiments, which is of fundamental significance for further study of its physical and chemical properties. Moreover, the influence of entropy increment on the stability of Ca2FeAlO5 crystal is clarified, which paves the way to investigate the structures and properties of Ca2FeAlO5 and other brownmillerite members.

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Section: Introductionmentioning

confidence: 99%

Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective

Tao

Zhang

et al. 2019

J Am Ceram Soc

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“…(STO), is the base material for the emerging field of oxide electronics. Two-dimensional electron gases (2DEGs) at STO-based heterointerfaces, [1][2][3][4] LaAlO3/SrTiO3 (LAO/STO) in particular, 1 exhibit a large number of remarkable physical properties, such as superconductivity, 5 magnetism, 6 sensitivity to electric field, 7 light illumination, 8 and high electron mobility, [9][10] which show potential applications in the next generation of electronic devices. 11 Despite intensive research, the origin of the conductivity at the LAO/STO interface remains hotly debated.…”

Section: Introductionmentioning

confidence: 99%

Tuning the Two-Dimensional Electron Gas at Oxide Interfaces with Ti–O Configurations: Evidence from X-ray Photoelectron Spectroscopy

Gan

Niu

Norrman

et al. 2017

ACS Appl. Mater. Interfaces

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A chemical redox reaction can lead to a two-dimensional electron gas at the interface between a TiO-terminated SrTiO (STO) substrate and an amorphous LaAlO capping layer. When replacing the STO substrate with rutile and anatase TiO substrates, considerable differences in the interfacial conduction are observed. On the basis of X-ray photoelectron spectroscopy (XPS) and transport measurements, we conclude that the interfacial conduction comes from redox reactions, and that the differences among the materials systems result mainly from variations in the activation energies for the diffusion of oxygen vacancies at substrate surfaces.

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“…This results in, for example, the observation of quantum Hall effect in delta‐doped STO and in a LaMnO 3 (LMO) buffered LAO/STO heterointerface . Among the various capping or buffer layers of manganites and cuprates used, the introduction of an electron sink of polar LMO as a buffer layer at the LAO/STO interface is of particular interest, which provides a more effective modulation‐doping effect than the capping layer cases as well as a strong suppression of oxygen vacancies on the STO side …”

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confidence: 99%

Diluted Oxide Interfaces with Tunable Ground States

et al. 2019

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as 2D superconductivity (SC), [4][5][6][7][8] magnetism, [9][10][11] and possible coexistence of these two, [12][13][14] providing an intriguing platform for multifunctional electronic devices.The carriers in the 2DEL of STObased heterostructures occupy the Ti 3d t 2g orbitals, where the in-plane d xy bands often have a lower energy than the out-ofplane oriented d xz /d yz due to the confinement of these orbitals at the interface. [1,15] Among the systems investigated so far, the epitaxial polar/nonpolar LAO/STO interface has drawn intensive attention and shows a typical carrier density, n s , of ≈4 × 10 13 cm −2 . [4] This high carrier density results in the population of orbitals with both d xy and d xz /d yz symmetry. The occupation of carriers in different subbands has previously been controlled reversibly using electrostatic gating, leading to a versatile tuning of the physical properties of the interface. [16] For example, by back gating the interface through the STO substrate, a Lifshitz transition was revealed at a critical carrier density of n c = 1.7 × 10 13 cm −2 , [6] above which the Fermi level starts to cross the bottom of the d xz /d yz bands. In proximity to n c , superconductivity exhibits a dome-shape as a function of gating voltage The metallic interface between two oxide insulators, such as LaAlO 3 /SrTiO 3 (LAO/STO), provides new opportunities for electronics and spintronics. However, due to the presence of multiple orbital populations, tailoring the interfacial properties such as the ground state and metal-insulator transitions remains challenging. Here, an unforeseen tunability of the phase diagram of LAO/STO is reported by alloying LAO with a ferromagnetic LaMnO 3 insulator without forming lattice disorder and at the same time without changing the polarity of the system. By increasing the Mn-doping level, x, of LaAl 1−x Mn x O 3 / STO (0 ≤ x ≤ 1), the interface undergoes a Lifshitz transition at x = 0.225 across a critical carrier density of n c = 2.8 × 10 13 cm −2 , where a peak T SC ≈255 mK of superconducting transition temperature is observed. Moreover, the LaAl 1−x Mn x O 3 turns ferromagnetic at x ≥ 0.25. Remarkably, at x = 0.3, where the metallic interface is populated by only d xy electrons and just before it becomes insulating, a same device with both signatures of superconductivity and clear anomalous Hall effect (7.6 × 10 12 cm −2 < n s ≤ 1.1 × 10 13 cm −2 ) is achieved reproducibly. This provides a unique and effective way to tailor oxide interfaces for designing on-demand electronic and spintronic devices. Oxide InterfacesThe surface of SrTiO 3 (STO) [1] or its interface to another oxide insulator such as the polar perovskite LaAlO 3 (LAO) [2] or the spinel γ-Al 2 O 3 [3] can host a 2D electron liquid (2DEL). In particular, the 2DEL at LAO/STO interface has been found to exhibit a wide spectrum of emergent phenomena such

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Tuning the Two-Dimensional Electron Liquid at Oxide Interfaces by Buffer-Layer-Engineered Redox Reactions

Cited by 24 publications

References 36 publications

Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective

Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective

Tuning the Two-Dimensional Electron Gas at Oxide Interfaces with Ti–O Configurations: Evidence from X-ray Photoelectron Spectroscopy

Diluted Oxide Interfaces with Tunable Ground States

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Tuning the Two-Dimensional Electron Liquid at Oxide Interfaces by Buffer-Layer-Engineered Redox Reactions

Cited by 24 publications

References 36 publications

Atomic occupancy mechanism in brownmillerite Ca2FeAlO5 from a thermodynamic perspective

Atomic occupancy mechanism in brownmillerite Ca2FeAlO5 from a thermodynamic perspective

Tuning the Two-Dimensional Electron Gas at Oxide Interfaces with Ti–O Configurations: Evidence from X-ray Photoelectron Spectroscopy

Diluted Oxide Interfaces with Tunable Ground States

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Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective

Atomic occupancy mechanism in brownmillerite Ca₂FeAlO₅ from a thermodynamic perspective