Physics of SrTiO<sub>3</sub>-based heterostructures and nanostructures: a review

Pai, Yun‐Yi; Tylan‐Tyler, Anthony; Irvin, Patrick; Levy, Jeremy

doi:10.1088/1361-6633/aa892d

Cited by 263 publications

(205 citation statements)

References 542 publications

(1,118 reference statements)

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“…a value compatible with experimental measurements 34,38 in the limit of low values of particle density. Finally, in order to assess the topological character of the superconducting phase for the nanowire we observe that, due to the applied magnetic field, the time reversal symmetry is broken in the examined nanowires.…”

Section: Model and Methodologysupporting

confidence: 90%

Evolution of topological superconductivity by orbital-selective confinement in oxide nanowires

et al. 2019

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We determine the optimal conditions to achieve topological superconducting phases having spinsinglet pairing for a planar nanowire with finite lateral width in the presence of an in-plane external magnetic field. We employ a microscopic description that is based on a three-band electronic model including both the atomic spin-orbit coupling and the inversion asymmetric potential at the interface between oxide band-gap insulators. We consider amplitudes of the pairing gap, spin-orbit interactions and electronic parameters that are directly applicable to nanowires of LaAlO3-SrTiO3. The lateral confinement introduces a splitting of the d-orbitals that alters the orbital energy hierarchy and significantly affects the electron filling dependence of the topological phase diagram. Due to the orbital directionality of the t2g-states, we find that in the regime of strong confinement the onset of topological phases is pinned at electron filling where the quasi flat heavy bands start to get populated. The increase of the nanowire thickness leads to a changeover from sparse-to-dense distribution of topologically non-trivial domains which occurs at the cross-over associated to the orbital population inversion. These findings are corroborated by a detailed analysis of the most favorable topological superconducting phases in the electron doping-magnetic field plane highlighting the role of orbital selective confinement.

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Section: Model and Methodologysupporting

confidence: 90%

Evolution of topological superconductivity by orbital-selective confinement in oxide nanowires

et al. 2019

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“…Strain (stress) is a wonderful approach to manipulate crystal structures of perovskite oxides and thus control their electronic structures and functional properties [3,8,9,19,21]. Here, through first-principles calculations, we show that biaxial stress can be used to create tunable surface 2DEG and 2DHG and then drive sign interchange of the 2D carrier gases in KTO thin film.…”

Section: Introductionmentioning

confidence: 92%

Strain-driven carrier-type switching of surface two-dimensional electron and hole gases in a KTaO₃ thin film

Zhang

Liu

2018

Phys. Chem. Chem. Phys.

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Since the discovery of a two-dimensional (2D) electron gas at the LaAlO/SrTiO interface, 2D carrier gases at such oxide interfaces and surfaces have attracted great attention because they can host many important phenomena and may produce novel functional devices. Here, we show through first-principles investigations that the surface 2D electron and hole gases in a KTaO (KTO) thin film can be tuned by applying biaxial stress. When increasing compressive in-plane strain, the 2D carrier concentrations decrease down to zero and then a new pair of surface 2D electron and hole gases appears in which the carrier types are switched to the opposite ones. Our analysis indicates that this carrier-type switching occurs because the increasing compressive strain reverses the slope of monolayer-resolved electrostatic potential along the [001] direction. We also present strain-dependent carrier concentrations and effective masses, and explore their thickness dependence. It is further shown that the 2D carrier gases and their strain-driven carrier-type switching across the KTO layer still remain true in the presence of overlayers and epitaxial substrates. These phenomena should be useful to design novel functional devices.

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“…The strong Rashba coupling in LAO/STO has led to the realization of various spintronics effects such as spin-to-charge conversions [24][25][26][27][28] and spin-orbit torques [29]. The fact that these phenomena are interfacial in nature allows us a much better degree of external control of its electrical and magnetic properties compared to conventional spintronic materials such as ferromagnetic metals [30,31]. More importantly from the application standpoint, the conducting layer is protected against external perturbations as it is sandwiched between conventional oxides insulators [30,31], which makes it more robust in comparison to the exposed surface states of topological insulators.…”

Section: Introductionmentioning

confidence: 99%

Tunable spin and orbital polarization in SrTiO₃-based heterostructures

Kong

Yang

et al. 2019

New J. Phys.

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We formulate the effective Hamiltonian of Rashba spin-orbit coupling (RSOC) in LaAlO SrTiO 3 3(LAO/STO) heterostructures. We derive analytical expressions of properties, e.g. Rashba parameter, effective mass, band edge energy and orbital occupancy, as functions of material and tunable heterostructure parameters. While linear RSOC is dominant around the Γ-point, cubic RSOC becomes significant at the higher-energy anti-crossing region. We find that linear RSOC stems from the structural inversion asymmetry (SIA), while the cubic term is induced by both SIA and bulk asymmetry. Furthermore, the SOC strength shows a striking dependence on the tunable heterostructure parameters such as STO thickness and the interfacial electric field which is ascribed to the quantum confinement effect near the LAO/STO interface. The calculated values of the linear and cubic RSOC are in agreement with previous experimental results.the SOC which accounts for the properties of the heterostructure, had been deliberately introduced, and the contribution of the bulk STO as well as the inter-orbital hopping was ignored. Significantly, the large spin splitting at the anti-crossing region, a signature of the multi-orbital effects, has not been fully elucidated.Recently, a theory based on k.p model [35, 36], including the contribution of the bulk STO, predicted a spin splitting induced by the inter-orbital hopping and interfacial band-bending. However, a complete picture of the multi-orbital Rashba SOC is still lacking. In this work, we aim to construct the effective Hamiltonian of Rashba spin-orbit coupling system in STObased structures, taking into account the underlying factors such as the confinement effect, as well as interface effects including inversion symmetry breaking (ISB) and band-bending. We derive analytical expressions of properties, e.g. Rashba parameter, effective mass, band edge energy and orbital occupancy, as functions of material and tunable heterostructure parameters. We show that the type and strength of spin-orbit coupling as well as the orbital selectivity are tunable by controlling geometric factor such as STO thickness and by applying electric field via gate voltage. The thickness and gate control of SOC provides a possible avenue for optimization of Rashba SOC for spintronics applications and devices.

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Physics of SrTiO₃-based heterostructures and nanostructures: a review

Cited by 263 publications

References 542 publications

Evolution of topological superconductivity by orbital-selective confinement in oxide nanowires

Evolution of topological superconductivity by orbital-selective confinement in oxide nanowires

Strain-driven carrier-type switching of surface two-dimensional electron and hole gases in a KTaO₃ thin film

Tunable spin and orbital polarization in SrTiO₃-based heterostructures

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Physics of SrTiO3-based heterostructures and nanostructures: a review

Cited by 263 publications

References 542 publications

Evolution of topological superconductivity by orbital-selective confinement in oxide nanowires

Evolution of topological superconductivity by orbital-selective confinement in oxide nanowires

Strain-driven carrier-type switching of surface two-dimensional electron and hole gases in a KTaO3 thin film

Tunable spin and orbital polarization in SrTiO3-based heterostructures

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Physics of SrTiO₃-based heterostructures and nanostructures: a review

Strain-driven carrier-type switching of surface two-dimensional electron and hole gases in a KTaO₃ thin film

Tunable spin and orbital polarization in SrTiO₃-based heterostructures