Strontium titanate has emerged as a promising material for oxide-based electronics due to its versatile electronic properties and compatibility with cation doping. This study investigates the giant persistent photoconductivity (PPC) in ultrathin La-doped SrTiO3 (La:STO) films. We demonstrate that, unlike conventional PPC mechanisms based on oxygen vacancies, a strong and robust PPC can be triggered by activating electrons localized at Ti ions near the surface of La:STO films, where electron-lattice coupling plays a pivotal role. Specifically, for the 8-unit-cell-thick La:STO films, the Ti-related PPC of 1276 % is achieved under exposure to ultraviolet (UV) light with a wavelength of 405 nm. This PPC state remains highly stable, with full release taking >24 h at room temperature. Our first-principles density functional theory calculations and thickness-dependent photocurrent analysis consistently reveal that this giant PPC originates from electrons activated at Ti3+O6 octahedra located near the surface of the La:STO layer. These results demonstrate that electron-lattice interactions in transition metal oxides can give rise to strong PPC characteristics, suggesting future applications in low-dimensional optoelectronic devices. (c) 2025 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.

Ferromagnetic perovskite oxides, particularly La0.7​Sr0.3MnO3 (LSMO), show significant promise for spintronics and electromagnetic applications due to their unique half-metallicity and colossal magnetoresistance properties. These properties are known to arise from Mn-O-Mn double-exchange interactions, which are directly related to microscopic lattice structures. However, since the microscopic structure in LSMO is highly sensitive to various material parameters, such as thickness, lattice strain, oxygen deficiency, and cation stoichiometry, understanding the intricate relationship between the microscopic structures and the resulting physical properties of LSMO remains challenging. Herein, a machine learning approach is introduced to characterize ferromagnetic LSMO thin films by featurization of their surface morphology. Using an ensemble machine learning method, the non-linear correlations between surface morphology and the electronic, magnetic properties of LSMO thin films are captured and modeled. Based on these estimated correlations, LSMO thin films are classified into five representative types, each characterized by distinctive properties and surface morphologies. These results imply that surface morphology can reveal hidden information about the strongly correlated properties of ferromagnetic LSMO thin films. Consequently, the machine learning-based approach provides an efficient method for understanding the correlated material properties of ferromagnetic oxides and related materials through surface morphology analysis.

Interface engineering at complex oxide heterostructures enables a wide range of electronic functionalities critical for next‐generation devices. Here it is demonstrated that ultra‐low‐voltage electron beam lithography (ULV‐EBL) creates high‐quality mesoscale structures at LaAlO 3 /SrTiO 3 (LAO/STO) interfaces with greater efficiency than conventional methods. Nanowires, tunnel barriers, and electron waveguides are successfully patterned that exhibit distinctive transport characteristics including 1D superconductivity, nonlinear current–voltage behavior, and ballistic electron flow. While conductive atomic force microscopy (c‐AFM) previously enabled similar interface modifications, ULV‐EBL provides significantly faster patterning speeds (10 mm s −1 vs 1 µm s −1 ), wafer‐scale capability (>(10 cm) 2 vs <(90 µm) 2 ), and maintenance of pattern quality under vacuum conditions. Additionally, an efficient oxygen plasma treatment method is developed for pattern erasure and surface cleaning, which reveals novel surface reaction dynamics at oxide interfaces. These capabilities establish ULV‐EBL as a versatile approach for scalable interface engineering in complex oxide heterostructures, with potential applications in reconfigurable electronics, sensors, and oxide‐based devices.

Two-level systems based on point defects in dielectric oxides offer promising entropy source for random number generators. The random telegraph noise (RTN) generated by the two-level systems is ideal for creating random bit-strings for advanced computing and cryptographic technologies. However, in classical oxide systems, RTN signals often suffer from instability due to undesired defect migration and metastable electronic states. Herein, we present a two-level quantum system based on SrRuO3/LaAlO3/Nb-doped SrTiO3 heterostructure, which incorporates two different types of point defects, oxygen vacancies and antisite Ti defects. Temporal electron localization at antisite defects alters the energy levels of nearby oxygen vacancies through instantaneous Coulomb interaction, resulting in two-level current fluctuation across the interface. The RTN-like current signals exhibit high stability at room temperature. We utilize the stable two-level fluctuations to generate random bit-strings and confirm their applicability in practical stochastic machine learning algorithms for image super-resolution. This study provides a guideline for designing reliable entropy sources by exploiting the complementary interactions between cation and anion point defects in oxide-based electronic systems, essential for hardware-based random number generators.

Conductive atomic force microscope (c-AFM) lithography can be utilized to create a wide range of LaAlO3 /SrTiO3 (LAO/STO)-based nanoelectronic devices in a reconfigurable manner. Experiments were generally performed with intrinsically insulating LAO/STO heterostructures, with LAO thickness less than the critical value at which a polar catastrophe takes place [< 4 unit cell (u.c.)]. Here, we use inductively coupled plasma reactive ion etching (ICPRIE) to fabricate c-AFM "canvases" on intrinsically conducting LAO/STO samples with >= 4 u.c. LAO. We observe that its interfacial two-dimensional electron gas (2DEG) can be pinched off and then switched back on by c-AFM lithography. Nanowires created with initially conductive LAO/STO interfaces have an order-of-magnitude longer lifetime in ambient conditions, when compared to an identically created 3.4 u.c. LAO/STO nanowire. We also demonstrate key nanoscale properties such as ballistic transport in a quasi-one-dimensional electron waveguide at a 5 u.c. LAO/STO interface. This approach frees c-AFM-written nanodevice designs from time constraints in air associated with <4 u.c. LAO/STO heterostructures. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution-NonCommercial 4.0International (CC BY-NC) license (https://creativecommons.org/licenses/by-nc/4.0/).

In oxide-based electronic systems, polar point defects act as charge traps and strongly influence the electrical properties of these systems. While cation antisite defects are commonly present in oxides and give rise to intriguing physical phenomena such as ferroelectricity, spin ordering, and cathodoluminescence, their fundamental charge trapping characteristics remain elusive. Herein, we demonstrate that antisite Ti defects (Ti-Sr) can serve as significant charge traps in SrTiO3 (STO). The formation of Ti-Sr defects was precisely controlled by adjusting the cation stoichiometry of STO, as verified by low-temperature photoluminescence and Raman spectroscopy. The charge trapping of Ti-Sr defects was then directly examined through low-frequency noise measurements of ultrathin SrRuO3 (SRO) channels, which were in-situ grown on the stoichiometry-controlled STO. The SRO channel on STO films with a higher density of Ti-Sr defects shows a unique feature of two Lorentzian noise components, while that on stoichiometric STO exhibits a typical 1/f-type noise. Our analysis of the thermal activation process reveals that Ti-Sr defect-induced charge trapping can occur with a quite low activation energy of similar to 0.044 eV due to interfacial band shift. These results suggest that cation-related point defects, which have previously been underestimated, can significantly impact the electronic properties of oxide-based electronic systems.

Interface engineering at complex oxide heterostructures enables a wide range of electronic functionalities critical for next-generation devices. Here it is demonstrated that ultra-low-voltage electron beam lithography (ULV-EBL) creates high-quality mesoscale structures at LaAlO3/SrTiO3 (LAO/STO) interfaces with greater efficiency than conventional methods. Nanowires, tunnel barriers, and electron waveguides are successfully patterned that exhibit distinctive transport characteristics including 1D superconductivity, nonlinear current-voltage behavior, and ballistic electron flow. While conductive atomic force microscopy (c-AFM) previously enabled similar interface modifications, ULV-EBL provides significantly faster patterning speeds (10 mm s(-)(1) vs 1 mu m s(-)(1)), wafer-scale capability (>(10 cm)(2) vs <(90 m)(2)), and maintenance of pattern quality under vacuum conditions. Additionally, an efficient oxygen plasma treatment method is developed for pattern erasure and surface cleaning, which reveals novel surface reaction dynamics at oxide interfaces. These capabilities establish ULV-EBL as a versatile approach for scalable interface engineering in complex oxide heterostructures, with potential applications in reconfigurable electronics, sensors, and oxide-based devices.

Point defects in complex oxide thin films play a critical role in determining material properties but remain challenging to control with precision. This study introduces metal-organic pulsed laser deposition (MOPLD) as a novel synthesis technique for the precise manipulation of these defects, using LaAlO3/SrTiO3 (LAO/STO) as a model system. By employing titanium tetraisopropoxide (TTIP) as the titanium precursor, MOPLD achieves refined stoichiometric control in STO layers while preserving their structural integrity, as confirmed by X-ray diffraction and Raman spectroscopy. Depth-resolved cathodoluminescence spectroscopy and density functional theory calculations reveal that increasing TTIP flux during STO growth enhances the [TiSr]/[VSr] ratio and reduces the [VO] concentration. These defect modifications lead to a significant improvement in the low-temperature mobility of the two-dimensional electron gas at the LAO/STO interface, evidenced by distinct Shubnikov-de Haas oscillations. This work underscores the potential of MOPLD to advance defect engineering in complex oxide heterostructures, opening new avenues for quantum material research.

Since the discovery of two-dimensional electron gas at the LaAlO3/SrTiO3 interface, its intriguing physical properties have garnered significant interests for device applications. Yet, understanding its response to electrical stimuli remains incomplete. Our in-situ transmission electron microscopy analysis of a LaAlO3/SrTiO3 two-dimensional electron gas device under electrical bias reveals key insights. Inline electron holography visualized the field-induced modulation of two-dimensional electron gas at the interface, while electron energy loss spectroscopy showed negligible electromigration of oxygen vacancies. Instead, atom-resolved imaging indicated that electric fields trigger polar distortion in the LaAlO3 layer, affecting two-dimensional electron gas modulation. This study refutes the previously hypothesized role of oxygen vacancies, underscoring the lattice flexibility of LaAlO3 and its varied polar distortions under electric fields as central to two-dimensional electron gas dynamics. These findings open pathways for advanced oxide nanoelectronics, exploiting the interplay of polar and nonpolar distortions in LaAlO3.

Photodetectors that detect near-infrared (NIR) light serve as important components in contemporary energy-efficient optoelectronic devices. However, detecting the low-energy photons of the NIR light has long been challenging since the ease of photoexcitation inevitably involves increasing the background current in the dark. Herein, we report the atomic-scale interface modification in SrRuO3/LaAlO3/Nb-doped SrTiO3 (SRO/LAO/Nb:STO) heterostructures for NIR photodetection. The interfacial band alignment by a polar monolayer LAO allows precise tuning of the Schottky barrier to achieve a specific energy band profile suitable for the NIR photodetection. The SRO/LAO/Nb:STO heterojunctions show a high photoresponsivity up to similar to 1.1 mA/W under NIR light irradiation (lambda = 850 nm), while keeping the pA-scale dark current. The increase in the responsivity by interface modification is evaluated at a maximum of 1371%. Based on the enhanced NIR photoresponsivity, as a proof of concept, we demonstrate the spatial imaging of NIR signals using a conceptual array of SRO/LAO/Nb:STO heterojunctions. In addition, the experimental-data-based simulation verifies that the array device can implement pulse-number-dependent plasticity, which is based on the characteristic persistent photoconductivity. This study suggests that atomic-scale interface modification is a facile and powerful method for optimizing the photoresponsive properties of complex-oxide-based heterojunctions.

Emulating synaptic functionalities in optoelectronic devices is significant in developing artificial visual-perception systems and neuromorphic photonic computing. Persistent photoconductivity (PPC) in metal oxides provides a facile way to realize the optoelectronic synaptic devices, but the PPC performance is often limited due to the oxygen vacancy defects that release excess conduction electrons without external stimuli. Herein, a high-performance optoelectronic synapse based on the stoichiometry-controlled LaAlO3/SrTiO3 (LAO/STO) heterostructure is developed. By increasing La/Al ratio up to 1.057:1, the PPC is effectively enhanced but suppressed the background conductivity at the LAO/STO interface, achieving strong synaptic behaviors. The spectral noise analyses reveal that the synaptic behaviors are attributed to the cation-related point defects and their charge compensation mechanism near the LAO/STO interface. The short-term and long-term plasticity is demonstrated, including the paired-pulse facilitation, in the La-rich LAO/STO device upon exposure to UV light pulses. As proof of concepts, two essential synaptic functionalities, the pulse-number-dependent plasticity and the self-noise cancellation, are emulated using the 5 × 5 array of La-rich LAO/STO synapses. Beyond the typical oxygen deficiency control, the results show how harnessing the cation stoichiometry can be used to design oxide heterostructures for advanced optoelectronic synapses and neuromorphic applications.

A wide family of two dimensional (2D) systems, including stripe-phase superconductors, sliding Luttinger liquids, and anisotropic 2D materials, can be modeled by an array of coupled one-dimensional (1D) electron channels or nanowire arrays. Here we report experiments in arrays of conducting nanowires with gate and field tunable interwire coupling, that are programmed at the LaAlO_3/SrTiO_3 interface. We find a magnetically-tuned metal-to-insulator transition in which the transverse resistance of the nanowire array increases by up to four orders of magnitude. To explain this behavior, we develop a minimal model of a coupled two-wire system which agrees well with observed phenomena. These nanowire arrays can serve as a model systems to understand the origin of exotic behavior in correlated materials via analog quantum simulation.

The LaAlO3/SrTiO3 interface hosts a plethora of gate-tunable electronic phases. Gating of LaAlO3/SrTiO3 interfaces is usually assumed to occur electrostatically. However, increasing evidence suggests that non-local interactions can influence and, in some cases, dominate the coupling between applied gate voltages and electronic properties. Here, quasi-1D ballistic electron waveguides are sketched at the LaAlO3/SrTiO3 interface as a probe to understand how gate tunability varies as a function of spatial separation. Gate tunability measurements reveal the scaling law to be at odds with the pure electrostatic coupling observed in traditional semiconductor systems. The non-Coulombic gating at the interface is attributed to a long-range nanoelectromechanical coupling between the gate and electron waveguide, possibly mediated by the ferroelastic domains in SrTiO3. The long-range interactions at the LaAlO3/SrTiO3 interface add unexpected richness and complexity to this correlated electron system.

KTaO3 has recently attracted attention as a model system to study the interplay of quantum paraelectricity, spin-orbit coupling, and superconductivity. However, the high and low vapor pressures of potassium and tantalum present processing challenges to creating interfaces clean enough to reveal the intrinsic quantum properties. Here, we report superconducting heterostructures based on electronic-grade epitaxial (111) KTaO3 thin films. Electrical and structural characterizations reveal that two-dimensional electron gas at the heterointerface between amorphous LaAlO3 and KTaO3 thin film exhibits significantly higher electron mobility, superconducting transition temperature and critical current density than those in bulk single crystal KTaO3-based heterostructures owing to cleaner interface in KTaO3 thin films. Our hybrid approach may enable epitaxial growth of other alkali metal-based oxides that lie beyond the capabilities of conventional methods.

We report the low -frequency noise behaviors in quasi -two-dimensional (quasi -2D) electron systems based on complex oxide heterostructures. First, the surface 2D electron gas (2DEG) on SrTiO3 (STO) exhibits the 1/f alpha-type current power spectral density (PSD) with alpha similar to 1.39. The non -unity exponent alpha indicates the discrepancy between the depth distributions of electrons and oxygen vacancies in the STO substrate. Second, the amorphous LaAlO3/ KTaO3 (LAO/KTO) interface, another quasi -2D electron system, shows Lorentzian components of PSD at a highfrequency region around 1 kHz, implying that the amorphous overlayer can provide additional shallow chargetrapping sites to the quasi -2D electrons in the crystalline KTO substrate. Lastly, ultrathin SrRuO3 (SRO) film grown on STO substrate exhibits the Lorentzian components of PSD at a low -frequency region around 200 Hz. The slight suppression of the fast charge trapping is attributed to the intrinsic band bending at the interface between film and substrate. These results will provide a guideline for understanding the defect -induced charge trapping and the relevant electron dynamics in the quasi -2D electron systems as well as the oxide -based electronic materials in general.

Charge ordering (CO), characterized by a periodic modulation of electron density and lattice distortion, has been a fundamental topic in condensed matter physics, serving as a potential platform for inducing novel functional properties. The charge-ordered phase is known to occur in a doped system with high d -electron occupancy, rather than low occupancy. Here, we report the realization of the charge-ordered phase in electron-doped (100) SrTiO 3 epitaxial thin films that have the lowest d -electron occupancy i.e., d 1 - d 0 . Theoretical calculation predicts the presence of a metastable CO state in the bulk state of electron-doped SrTiO 3 . Atomic scale analysis reveals that (100) surface distortion favors electron-lattice coupling for the charge-ordered state, and triggering the stabilization of the CO phase from a correlated metal state. This stabilization extends up to six unit cells from the top surface to the interior. Our approach offers an insight into the means of stabilizing a new phase of matter, extending CO phase to the lowest electron occupancy and encompassing a wide range of 3 d transition metal oxides.

The LaAlO_3/SrTiO_3 interface hosts a plethora of gate-tunable electronic phases. Gating of LaAlO_3/SrTiO_3 interfaces are usually assumed to occur electrostatically. However, increasing evidence suggests that non-local interactions can influence and, in some cases, dominate the coupling between applied gate voltages and electronic properties. Here, we sketch quasi-1D ballistic electron waveguides at the LaAlO_3/SrTiO_3 interface as a probe to understand how gate tunability varies as a function of spatial separation. Gate tunability measurements reveal the scaling law to be at odds with the pure electrostatic coupling observed in traditional semiconductor systems. The non-Coulombic gating at the interface is attributed to the existence of a long-range nanoelectromechanical coupling between the gate and electron waveguide, mediated by the ferroelastic domains in SrTiO_3. The long-range interactions at the LaAlO_3/SrTiO_3 interface add unexpected richness and complexity to this correlated electron system.