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Register a new userOxygen-vacancy-induced charge carrier in n-type interface of LaAlO3 overlayer on SrTiO3 (001): interface vs bulk doping carrier
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We investigated the role of oxygen vacancy in n-type interface of LaAlO3 (LAO) overlayer on SrTiO3 (STO) (001) by carrying out density-functional-theory calculations. Comparing the total energies of the configurations with one vacancy in varying locations we found that oxygen vacancies favor to appear first in LAO surface. These oxygen vacancies in the surface generate a two-dimensional distribution of carriers at the interface, resulting in band bending at the interface in STO side. Dependent on the concentration of oxygen vacancies in LAO surface, the induced carrier charge at the interface partially or completely compensates the polar electric field in LAO. Moreover, the electronic properties of oxygen vacancies in STO are also presented. Every oxygen vacancy in STO generates two electron carriers, but this carrier charge has no effect on screening polar field in LAO. Band structures at the interface dependent on the concentrations of oxygen vacancies are presented and compared with experimental results.
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Modifications of the electronic bands of thin FeSe films due to oxygen vacancies in the supporting SrTiO 3 (001) substrate - and the interplay with spin-orbit coupling, magnetism, and epitaxy - are investigated by first-principles supercell calculations. Unfolded (k-projected) bands show that the oxygen vacancies both provide electron doping to the interface FeSe layer and also have notable effects on the details of the bands around the Fermi level, including renormalizing the width of the Fe-3d band near the Fermi level by a factor of about 0.6, and causing a splitting of ~40 meV at the M point for the checkerboard antiferromagnetic configuration. For an FeSe bilayer, the modifications to the bands are mainly limited to the interface FeSe layer. While spin-orbit-coupling induced band splittings of ~30 meV at M for the ideal FeSe/SrTiO3 (001) interfaces are comparable to the splitting due to oxygen vacancies, the effects are not simply additive. Calculations and comparison to our scanning tunneling microscopy images of MBE-grown FeSe films on SrTiO3 (001) suggest that a common defect may be Se bound to an oxygen vacancy at the interface
The voltage-spectral density SV(f) of the 2-dimensional electron gas formed at the interface of LaAlO3 /SrTiO3 has been thoroughly investigated. The low-frequency component has a clear 1/f behavior with a quadratic bias current dependence, attributed to resistance fluctuations. However, its temperature dependence is inconsistent with the classical Hooge model, based on carrier-mobility fluctuations. The experimental results are, instead, explained in terms of carrier-number fluctuations, due to an excitation-trapping mechanism of the 2-dimensional electron gas.
Heterostructures and superlattices consisting of a prototype Mott insulator, GdTiO3, and the band insulator SrTiO3 are grown by molecular beam epitaxy and show intrinsic electronic reconstruction, approximately 1/2 electron per surface unit cell at each GdTiO3/SrTiO3 interface. The sheet carrier densities in all structures containing more than one unit cell of SrTiO3 are independent of layer thicknesses and growth sequences, indicating that the mobile carriers are in a high concentration, two-dimensional electron gas bound to the interface. These carrier densities closely meet the electrostatic requirements for compensating the fixed charge at these polar interfaces. Based on the experimental results, insights into interfacial band alignments, charge distribution and the influence of different electrostatic boundary conditions are obtained.
Two-dimensional electron gas (2DEG) formed at the interface between SrTiO3 (STO) and LaAlO3 (LAO) insulating layer is supposed to possess strong Rashba spin-orbit coupling. To date, the inverse Edelstein effect (i.e. spin-to-charge conversion) in the 2DEG layer is reported. However, the direct effect of charge-to-spin conversion, an essential ingredient for spintronic devices in a current induced spin-orbit torque scheme, has not been demonstrated yet. Here we show, for the first time, a highly efficient spin generation with the efficiency of ~6.3 in the STO/LAO/CoFeB structure at room temperature by using spin torque ferromagnetic resonance. In addition, we suggest that the spin transmission through the LAO layer at high temperature range is attributed to the inelastic tunneling via localized states in the LAO band gap. Our findings may lead to potential applications in the oxide insulator based spintronic devices.
Interplay of spin, charge, orbital and lattice degrees of freedom in oxide heterostructures results in a plethora of fascinating properties, which can be exploited in new generations of electronic devices with enhanced functionalities. The paradigm example is the interface between the two band insulators LaAlO3 and SrTiO3 (LAO/STO) that hosts two-dimensional electron system (2DES). Apart from the mobile charge carriers, this system exhibits a range of intriguing properties such as field effect, superconductivity and ferromagnetism, whose fundamental origins are still debated. Here, we use soft-X-ray angle-resolved photoelectron spectroscopy to penetrate through the LAO overlayer and access charge carriers at the buried interface. The experimental spectral function directly identifies the interface charge carriers as large polarons, emerging from coupling of charge and lattice degrees of freedom, and involving two phonons of different energy and thermal activity. This phenomenon fundamentally limits the carrier mobility and explains its puzzling drop at high temperatures.
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