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The two-dimensional hole gas (2DHG) at the polar LaAlO3/SrTiO3 interface remains elusive. Different from isostructural perovskite-type interfaces, the spinel/perovskite heterointerface of γ-Al2O3/SrTiO3 (GAO/STO) enables us to control interfacial states with sub-unit-cell precision. Herein, we present the epitaxial growth of fractionally doped GAO/STO heterointerfaces, where GAO is precisely doped on the scale of 1/4-unit-cell (0.2 nm) by ferromagnetic Fe3O4 and nonmagnetic ZnO atomic layers. Notably, the conduction of the engineered interfaces depends critically on the position of the dopant, where a coexistence of electron and hole conduction is measured at even sublayer-doped GAO/STO interfaces. First-principles density functional theory calculations indicate that electron conductivity is from the interfacial TiO2 layers of the STO substrate, while the hole conductivity is from the Zn-doped GAO film. The presence of hole conduction can be explained from the alternating structural feature of a doped layer without oxygen vacancies. This work sheds additional insight on the emergence of 2DHG at oxide interfaces and provides opportunities for atomically engineered oxide interfaces with non-isostructural layers.

The interface reconstruction in perovskite heterostructures caused by interfacial octahedral tilt/rotation and its effects on the spin, charge, and orbital degrees of freedom is a very attractive topic for correlated oxides. Here, we present a systematic investigation on tensely strained (110)-LaCoO3/La2/3Sr1/3MnO3/LaCoO3 trilayers, focusing on orbital reconstruction and accompanied effects. The most remarkable finding is the reordering of the energy levels of Mn-3d orbitals at the interface: the low-lying orbital becomes dx2-y2 for sandwiched La2/3Sr1/3MnO3 rather than d3z2-r2 as expected for a bare La2/3Sr1/3MnO3 film. Interlayer charge transfer via dx2-y2 orbitals is further detected as a driving force of orbital reconstruction. Due to spin–orbit coupling, the charge/orbital reconstruction produces a chain effect on the spin degree of freedom of the La2/3Sr1/3MnO3 layer, resulting in a dramatic spin reorientation by 90° in a film plane. The present work demonstrates how to tune macroscopic properties of correlated oxides via mutual coupling between different degrees of freedom.

Recently, a high mobility quasi-two-dimensional electron gas has been reported for the heterointerface between two insulating and nonmagnetic oxides of spinel γ-Al2O3 and perovskite SrTiO3 (STO). Herein, we fabricated the epitaxial heterostructure with Al-based magnetic spinel oxide MAl2O4 (M = Fe, Co, Ni) on perovskite STO. Remarkably, all the MAl2O4 (M = Fe, Co, Ni) films exhibit ferromagnetic behavior up to room temperature. Although FeAl2O4/STO is insulating, the NiAl2O4/STO and CoAl2O4/STO heterointerfaces are found to be highly metallic and exhibit the anomalous Hall effect (AHE) at temperatures below 30 K. Their Hall mobility is as high as 3 × 104 cm2 V−1 s−1, comparable to that of the γ-Al2O3/STO interface. There has been evidence of oxygen-vacancy-related magnetism in γ-Al2O3/STO at temperatures below 5 K, while the enhanced AHE in NiAl2O4/STO and CoAl2O4/STO likely comes from the magnetic proximity effect induced by the top ferromagnetic MAl2O4 spinel films.Recently, a high mobility quasi-two-dimensional electron gas has been reported for the heterointerface between two insulating and nonmagnetic oxides of spinel γ-Al2O3 and perovskite SrTiO3 (STO). Herein, we fabricated the epitaxial heterostructure with Al-based magnetic spinel oxide MAl2O4 (M = Fe, Co, Ni) on perovskite STO. Remarkably, all the MAl2O4 (M = Fe, Co, Ni) films exhibit ferromagnetic behavior up to room temperature. Although FeAl2O4/STO is insulating, the NiAl2O4/STO and CoAl2O4/STO heterointerfaces are found to be highly metallic and exhibit the anomalous Hall effect (AHE) at temperatures below 30 K. Their Hall mobility is as high as 3 × 104 cm2 V−1 s−1, comparable to that of the γ-Al2O3/STO interface. There has been evidence of oxygen-vacancy-related magnetism in γ-Al2O3/STO at temperatures below 5 K, while the enhanced AHE in NiAl2O4/STO and CoAl2O4/STO likely comes from the magnetic proximity effect induced by the top ferromagnetic MAl2O4 spinel films.

High mobility spin-polarized two-dimensional electron gas (2DEG) is crucially important for spintronic applications. Here, we report our investigations on the 2DEG fabricated by spin coating a LaAlO3 layer on a (001) SrTiO3 substrate with a La2/3Sr1/3MnO3 buffer layer. When the buffer layer is below 3 uc, the 2DGE is highly mobile. Corresponding to the layer thicknesses of 0, 1, and 2 uc, the Hall mobilities are ∼24 000 cm2/V s, ∼28 000 cm2/V s, and ∼59 600 cm2/V s at 2 K. In contrast, the 2DEG with a buffer layer of 3 uc shows a relatively low mobility (∼3000 cm2/V s). However, an anomalous Hall effect was observed in this 2DEG below 20 K, indicating a long range ferromagnetic order. This work demonstrates the great potential of the chemical method in gaining high quality spin-polarized 2DEGs at the LaAlO3/SrTiO3 interface.

Heterointerfaces between two insulators play a central role in the study of oxide electronics owing to a spectrum of emergent properties. Manipulating transport of the interface by light can result in significant modulation of the ground state and excite localized states. However, their dynamics and mechanisms of photogenerated carries remain unclear. Here, this study presents the dynamics of carrier density and mobility under and after light illumination by Hall effect over time. It is discovered that the density and mobility after light illumination obey a stretched exponential expression, further indicating that the variation of mobility caused by the electron-electron scattering plays an important role in the recovery process in addition to the reduction of carrier density. Meanwhile, a non-linear Hall resistance at the LaAlO3/SrTiO3 interface under the illumination of a 360 nm laser at low temperature is observed. Furthermore, the gating effect can tune the recovery process after light illumination and induce a disappearance of non-linear Hall resistance. The results provide the experimental support for detailed mechanisms of the nonequilibrium process and developing of all-oxide electronic devices based on heterointerfaces.Heterointerfaces between two insulators play a central role in the study of oxide electronics owing to a spectrum of emergent properties. Manipulating transport of the interface by light can result in significant modulation of the ground state and excite localized states. However, their dynamics and mechanisms of photogenerated carries remain unclear. Here, this study presents the dynamics of carrier density and mobility under and after light illumination by Hall effect over time. It is discovered that the density and mobility after light illumination obey a stretched exponential expression, further indicating that the variation of mobility caused by the electron-electron scattering plays an important role in the recovery process in addition to the reduction of carrier density. Meanwhile, a non-linear Hall resistance at the LaAlO3/SrTiO3 interface under the illumination of a 360 nm laser at low temperature is observed. Furthermore, the gating effect can tune the recovery process after light illumination a...

Two-dimensional electron gas (2DEG) has abundant properties, which motivate not only fundamental physical interest but also concepts for device designing. While most of the reported 2DEGs are based on SrTiO3, here we report on a systematic investigation on anatase TiO2-based 2DEG generated by ion irradiation. By irradiating the surface layer of the anatase TiO2 films with appropriate argon ion beams, we gained the 2DEGs with a thickness of 4 nm. Unique transport behaviours of a T−1/3 or ln(1/T) sheet resistance dependence below 100 K are observed depending on irradiation time. Unusually large positive MR is observed for which the magnetic field causes a strong shrinkage of electron wave functions, and fairly large negative MR is detected in the 2DEG, arising from the depression of magnetic scattering.

We presented a systemic investigation on the joint effect of gate bias and light illumination on a metallic LaAlO3/SrTiO3 interface in the temperature range from 15 K to 300 K. We showed that the photo excitation significantly enhanced the gating effect for the metallic two-dimensional electron gas. However, its effect is strongly temperature dependent; it is strong at low and high temperatures, and weak in the intermediate temperature range. There are evidences that the amplified gating effect stemmed from enhanced carrier depletion while the Hall mobility remains nearly unaffected. Acceleration of the gating process, together with a training effect marked by a strong dependence on gating history of the getting effect, is induced by repeating the electric cycling, indicating atomic reconfiguration due to oxygen migration and the memory of the migration paths.

Quasi-one-dimensional electron gases (q1DEGs) have been obtained by fabricating LaAlO3 nanowires, using the technique of electrostatic spinning plus post annealing, above TiO2-terminated SrTiO3 substrate. The q1DEG exhibits an electronic transport behavior of variable range hopping with the one dimension characteristic. Visible light illumination produces a strong effect on transport process, depressing the resistance of the q1DEG by a factor up to 8. As expected, gating effect is weak at relative high temperatures, ∼3.2% at 150 K and 1.5% at 300 K under a back gate of 200 V. Aided by light illumination, however, the gating effect is 35-fold amplified, and the resistance increases under not only negative gates but also positive gates, different from the normal gating effect without illumination. Possible explanations for these phenomena are given.

Atomic force microscope (AFM) users often calibrate the spring constants of cantilevers using functionality built into individual instruments. This is performed without reference to a global standard, which hinders robust comparison of force measurements reported by different laboratories. In this article, we describe a virtual instrument (an internet-based initiative) whereby users from all laboratories can instantly and quantitatively compare their calibration measurements to those of others - standardising AFM force measurements - and simultaneously enabling non-invasive calibration of AFM cantilevers of any geometry. This global calibration initiative requires no additional instrumentation or data processing on the part of the user. It utilises a single website where users upload currently available data. A proof-of-principle demonstration of this initiative is presented using measured data from five independent laboratories across three countries, which also allows for an assessment of current calibration., 34 pages, 14 figures

The crystal structures and magnetic properties of the 40 nm brownmillerite SrMnO2.5 film, perovskite SrMnO3-δ film, and mixed-phase film have been systematically investigated. The features of the oxygen vacancy ordering superstructure in the brownmillerite SrMnO2.5 film are observed from HRSTEM as follows: the dark stripes with a periodicity of four (110) planes of the cubic perovskite appearing at an angle of 45° with the substrate-film interface and extra reflection spots in fast Fourier transformation patterns along the (001) plane. When annealing the brownmillerite SrMnO2.5 film under higher oxygen pressure, the top portion undergoes structure transition into perovskite SrMnO3-δ as seen in the mixed-phase film consisting of the perovskite SrMnO3-δ phase dominating at the top part and the brownmillerite SrMnO2.5 phase dominating at the bottom part. The magnetic properties and Mn valences of the brownmillerite SrMnO2.5 film indicate that this film, similar to the bulk, is antiferromagnetic with TN at 37...