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Journal ArticleDOI

Defect dynamics and spectral observation of twinning in single crystalline LaAlO3 under subbandgap excitation

25 Jan 2011-Applied Physics Letters (American Institute of PhysicsAIP)-Vol. 98, Iss: 4, pp 041904
TL;DR: In this paper, the photoluminescence and ultrafast dynamics of LaAlO3 crystal were investigated and doublet splitting of roughly 6 nm is seen in these two sharp peaks, which arise from various defect levels within the bandgap.
Abstract: We have investigated the photoluminescence and ultrafast dynamics of LaAlO3 crystal. The photoluminescence consists of a broad spectrum and two sharp peaks, which arise from various defect levels within the bandgap. A doublet splitting of roughly 6 nm is seen in these two sharp peaks. An Al displacement of 0.09 A in a sublattice, which is possible because of twinning, is adequate to explain the spectral splitting. Femtosecond pump probe experiments reveal further that many of these defect levels have a few picosecond decay times while the lowest defect states have decay times longer than nanosecond to the valence band.
Citations
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Journal ArticleDOI
TL;DR: In this paper, a comprehensive comparison of (100)-oriented SrTiO3 substrates with crystalline and amorphous overlayers of LaAlO3 of different thicknesses prepared under different oxygen pressures was conducted.
Abstract: The relative importance of atomic defects and electron transfer in explaining conductivity at the crystalline LaAlO3/SrTiO3 interface has been a topic of debate. Metallic interfaces with similar electronic properties produced by amorphous oxide overlayers on SrTiO3 have called in question the original polarization catastrophe model. We resolve the issue by a comprehensive comparison of (100)-oriented SrTiO3 substrates with crystalline and amorphous overlayers of LaAlO3 of different thicknesses prepared under different oxygen pressures. For both types of overlayers, there is a critical thickness for the appearance of conductivity, but its value is always 4 unit cells (around 1.6 nm) for the oxygen-annealed crystalline case, whereas in the amorphous case, the critical thickness could be varied in the range 0.5 to 6 nm according to the deposition conditions. Subsequent ion milling of the overlayer restores the insulating state for the oxygen-annealed crystalline heterostructures but not for the amorphous ones. Oxygen post-annealing removes the oxygen vacancies, and the interfaces become insulating in the amorphous case. However, the interfaces with a crystalline overlayer remain conducting with reduced carrier density. These results demonstrate that oxygen vacancies are the dominant source of mobile carriers when the LaAlO3 overlayer is amorphous, while both oxygen vacancies and polarization catastrophe contribute to the interface conductivity in unannealed crystalline LaAlO3/SrTiO3 heterostructures, and the polarization catastrophe alone accounts for the conductivity in oxygen-annealed crystalline LaAlO3/SrTiO3 heterostructures. Furthermore, we find that the crystallinity of the LaAlO3 layer is crucial for the polarization catastrophe mechanism in the case of crystalline LaAlO3 overlayers.

182 citations

Journal ArticleDOI
TL;DR: A map of recent applications of hybrid functionals to perovskites is presented, aiming to cover an ample spectra of cases, and focuses on the technical aspects of the hybrid functional formalism, such as the role of the mixing and (for range-separated hybrids) screening parameters.
Abstract: After being used for years in the chemistry community to describe molecular properties, hybrid functionals have been increasingly and successfully employed for a wide range of solid state problems which are not accurately accessible by standard density functional theory. In particular, the upsurge of interest in transition metal perovskite-based compounds, motivated by their technological relevance and functional ductility, has incentivized the use of hybrid functionals for realistic applications, as hybrid functionals appear to be capable of capturing the complex correlated physics of this class of oxide material, characterized by a subtle coupling between several competing interactions (lattice, orbital, spin). Here we present a map of recent applications of hybrid functionals to perovskites, aiming to cover an ample spectra of cases, including the 'classical' 3d compounds (manganites, titanates, nickelates, ferrites, etc.), less conventional examples from the the 4d (technetiates) and 5d (iridates) series, and the (non-transition metal) sp perovskite BaBiO3. We focus our attention on the technical aspects of the hybrid functional formalism, such as the role of the mixing and (for range-separated hybrids) screening parameters, and on an extended array of physical phenomena: pressure- and doping-induced insulator-to-metal and structural phase transitions, multiferroism, surface and interface effects, charge ordering and localization effects, and spin-orbit coupling.

140 citations

Journal ArticleDOI
TL;DR: In this article, the authors observed ultrafast and reversible resistive switching in a thin-film device composed of a metallic platinum layer and two ultrathin layers of insulating oxides.
Abstract: Many commonly used electrical resistive switching devices are based on films of metal-oxide-metal ``sandwiches.'' Now scientists have observed ultrafast and reversible resistive switching in a thin-film device composed of a metallic platinum layer and two ultrathin layers of insulating oxides, LaAlO${}_{3}$ and SrTiO${}_{3}$, and revealed its origin in the oxides' charge-carrying oxygen vacancies.

72 citations

Journal ArticleDOI
TL;DR: The good linear relationship between the activity of RhB degradation and the coercive electric field indicates that the photocatalytic activity is closely related to the ferroelectric property.
Abstract: NaNbO(3) single-crystal films with (100), (110) and (111) oriented crystal planes were grown on LaAlO(3) (100), (110) and (111) substrates by pulsed laser deposition. The NaNbO(3) films exhibit anisotropy in the photocatalytic oxidization activity for Rhodamine B (RhB) degradation. The increasing order of RhB degradation in Ar atmosphere under full arc irradiation of a Xe lamp is (100) < (110) < (111), which is consistent with that of ˙OH generation. The good linear relationship between the activity of RhB degradation and the coercive electric field indicates that the photocatalytic activity is closely related to the ferroelectric property.

60 citations

Journal ArticleDOI
TL;DR: In this article, the X-ray excited optical luminescence response of sapphire (α-Al 2 O 3 ), aluminium lanthanate (LaAlO 3 ), and magnesium oxide (MgO) were measured at room temperature as a function of incident photon energy in the range from 500 to 1000 eV.

15 citations

References
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Journal ArticleDOI
TL;DR: A simple derivation of a simple GGA is presented, in which all parameters (other than those in LSD) are fundamental constants, and only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked.
Abstract: Generalized gradient approximations (GGA’s) for the exchange-correlation energy improve upon the local spin density (LSD) description of atoms, molecules, and solids. We present a simple derivation of a simple GGA, in which all parameters (other than those in LSD) are fundamental constants. Only general features of the detailed construction underlying the Perdew-Wang 1991 (PW91) GGA are invoked. Improvements over PW91 include an accurate description of the linear response of the uniform electron gas, correct behavior under uniform scaling, and a smoother potential. [S0031-9007(96)01479-2] PACS numbers: 71.15.Mb, 71.45.Gm Kohn-Sham density functional theory [1,2] is widely used for self-consistent-field electronic structure calculations of the ground-state properties of atoms, molecules, and solids. In this theory, only the exchange-correlation energy EXC › EX 1 EC as a functional of the electron spin densities n"srd and n#srd must be approximated. The most popular functionals have a form appropriate for slowly varying densities: the local spin density (LSD) approximation Z d 3 rn e unif

146,533 citations

Journal ArticleDOI
Peter E. Blöchl1
TL;DR: An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way and can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function.
Abstract: An approach for electronic structure calculations is described that generalizes both the pseudopotential method and the linear augmented-plane-wave (LAPW) method in a natural way. The method allows high-quality first-principles molecular-dynamics calculations to be performed using the original fictitious Lagrangian approach of Car and Parrinello. Like the LAPW method it can be used to treat first-row and transition-metal elements with affordable effort and provides access to the full wave function. The augmentation procedure is generalized in that partial-wave expansions are not determined by the value and the derivative of the envelope function at some muffin-tin radius, but rather by the overlap with localized projector functions. The pseudopotential approach based on generalized separable pseudopotentials can be regained by a simple approximation.

61,450 citations

Journal ArticleDOI
29 Jan 2004-Nature
TL;DR: A model interface is examined between two insulating perovskite oxides—LaAlO3 and SrTiO3—in which the termination layer at the interface is controlled on an atomic scale, presenting a broad opportunity to tailor low-dimensional charge states by atomically engineered oxide heteroepitaxy.
Abstract: Polarity discontinuities at the interfaces between different crystalline materials (heterointerfaces) can lead to nontrivial local atomic and electronic structure, owing to the presence of dangling bonds and incomplete atomic coordinations. These discontinuities often arise in naturally layered oxide structures, such as the superconducting copper oxides and ferroelectric titanates, as well as in artificial thin film oxide heterostructures such as manganite tunnel junctions. If polarity discontinuities can be atomically controlled, unusual charge states that are inaccessible in bulk materials could be realized. Here we have examined a model interface between two insulating perovskite oxides--LaAlO3 and SrTiO3--in which we control the termination layer at the interface on an atomic scale. In the simple ionic limit, this interface presents an extra half electron or hole per two-dimensional unit cell, depending on the structure of the interface. The hole-doped interface is found to be insulating, whereas the electron-doped interface is conducting, with extremely high carrier mobility exceeding 10,000 cm2 V(-1) s(-1). At low temperature, dramatic magnetoresistance oscillations periodic with the inverse magnetic field are observed, indicating quantum transport. These results present a broad opportunity to tailor low-dimensional charge states by atomically engineered oxide heteroepitaxy.

3,977 citations

Journal ArticleDOI
TL;DR: In this paper, the authors report on blue-light emission at room temperature from Ar+-irradiated, metallic SrTiO3 (STO) and propose a model by which the doped conduction electrons and the in-gap state produce a radiative process that results in blue light emission.
Abstract: Oxide-based electronic devices are expected to have fascinating properties, unlike those made from conventional semiconductors. SrTiO3 (STO) is a key material for this new field of electronics1,2,3,4,5,6,7,8,9,10,11. Here we report on blue-light emission at room temperature from Ar+-irradiated, metallic STO. The irradiation introduces oxygen deficiencies to a depth of ∼20 nm from the crystal surface. These deficiencies generate conduction carriers and stabilize a hole level in a self-trapped state. We propose a model by which the doped conduction electrons and the in-gap state produce a radiative process that results in blue-light emission. The emitting region can be patterned into any size and shape with conventional microscopic fabrication techniques.

531 citations

Journal ArticleDOI
TL;DR: It is found that, depending on specific growth protocols, the spatial extension of the high-mobility electron gas can be varied from hundreds of micrometres into SrTiO(3) to a few nanometres next to the LaAlO( 3)/SrTiO (3) interface.
Abstract: At the interface between complex insulating oxides, novel phases with interesting properties may occur, such as the metallic state reported in the LaAlO(3)/SrTiO(3) system . Although this state has been predicted and reported to be confined at the interface, some studies indicate a much broader spatial extension, thereby questioning its origin. Here, we provide for the first time a direct determination of the carrier density profile of this system through resistance profile mappings collected in cross-section LaAlO(3)/SrTiO(3) samples with a conducting-tip atomic force microscope (CT-AFM). We find that, depending on specific growth protocols, the spatial extension of the high-mobility electron gas can be varied from hundreds of micrometres into SrTiO(3) to a few nanometres next to the LaAlO(3)/SrTiO(3) interface. Our results emphasize the potential of CT-AFM as a novel tool to characterize complex oxide interfaces and provide us with a definitive and conclusive way to reconcile the body of experimental data in this system.

371 citations