Atomic-Scale Interface Modification in Complex Oxide Heterojunctions for Near-Infrared Photodetection.

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 SrRuO/LaAlO/Nb-doped SrTiO (SRO/LAO/Nb:STO) heterostructures for NIR photodetection.

Feld-induced modulation of two-dimensional electron gas at LaAlO/SrTiO interface by polar distortion of LaAlO.

Since the discovery of two-dimensional electron gas at the LaAlO/SrTiO 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 LaAlO/SrTiO two-dimensional electron gas device under electrical bias reveals key insights.

Electronic-grade epitaxial (111) KTaO heterostructures.

KTaO heterostructures have recently attracted attention as model systems 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 heterostructure interfaces clean enough to reveal the intrinsic quantum properties. Here, we report superconducting heterostructures based on high-quality epitaxial (111) KTaO thin films using an adsorption-controlled hybrid PLD to overcome the vapor pressure mismatch.

Surface triggered stabilization of metastable charge-ordered phase in SrTiO.

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 epitaxial thin films that have the lowest d-electron occupancy i.

Optoelectronic Synapse Based on 2D Electron Gas in Stoichiometry-Controlled Oxide Heterostructures.

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 LaAlO/SrTiO (LAO/STO) heterostructure is developed.

Electron pairing and nematicity in LaAlO/SrTiO nanostructures.

Strongly correlated electronic systems exhibit a wealth of unconventional behavior stemming from strong electron-electron interactions. The LaAlO/SrTiO (LAO/STO) heterostructure supports rich and varied low-temperature transport characteristics including low-density superconductivity, and electron pairing without superconductivity for which the microscopic origins is still not understood. LAO/STO also exhibits inexplicable signatures of electronic nematicity via nonlinear and anomalous Hall effects.

Geometrical Doping at the Atomic Scale in Oxide Quantum Materials.

Chemical dopants enabling a plethora of emergent physical properties have been treated as randomly and uniformly distributed in the frame of a three-dimensional doped system. However, in nanostructured architectures, the location of dopants relative to the interface or boundary can greatly influence device performance. This observation suggests that chemical dopants need to be considered as discrete defects, meaning that geometric control of chemical dopants becomes a critical aspect as the physical size of materials scales down into the nanotechnology regime.

Reversible Photomodulation of Two-Dimensional Electron Gas in LaAlO/SrTiO Heterostructures.

Long-lived photoinduced conductance changes in LaAlO/SrTiO (LAO/STO) heterostructures enable their use in optoelectronic memory applications. However, it remains challenging to quench the persistent photoconductivity (PPC) instantly and reproducibly, which limits the reversible optoelectronic switching. Herein, we demonstrate a reversible photomodulation of two-dimensional electron gas (2DEG) in LAO/STO heterostructures with high reproducibility.

Collective Control of Potential-Constrained Oxygen Vacancies in Oxide Heterostructures for Gradual Resistive Switching.

Filamentary resistive switching in oxides is one of the key strategies for developing next-generation non-volatile memory devices. However, despite numerous advantages, their practical applications in neuromorphic computing are still limited due to non-uniform and indeterministic switching behavior. Given the inherent stochasticity of point defect migration, the pursuit of reliable switching likely demands an innovative approach.

Strong Interfacial Charge Trapping in Ultrathin SrRuO on SrTiO Probed by Noise Spectroscopy.

SrRuO (SRO) has emerged as a promising quantum material due to its exotic electron correlations and topological properties. In epitaxial SRO films, electron scattering against lattice phonons or defects has been considered as only a predominant mechanism accounting for electronic properties. Although the charge trapping by polar defects can also strongly influence the electronic behavior, it has often been neglected.

Variance-aware weight quantization of multi-level resistive switching devices based on Pt/LaAlO/SrTiO heterostructures.

Resistive switching devices have been regarded as a promising candidate of multi-bit memristors for synaptic applications. The key functionality of the memristors is to realize multiple non-volatile conductance states with high precision. However, the variation of device conductance inevitably causes the state-overlap issue, limiting the number of available states.

Oxide Two-Dimensional Electron Gas with High Mobility at Room-Temperature.

The prospect of 2-dimensional electron gases (2DEGs) possessing high mobility at room temperature in wide-bandgap perovskite stannates is enticing for oxide electronics, particularly to realize transparent and high-electron mobility transistors. Nonetheless only a small number of studies to date report 2DEGs in BaSnO -based heterostructures. Here, 2DEG formation at the LaScO /BaSnO (LSO/BSO) interface with a room-temperature mobility of 60 cm  V  s at a carrier concentration of 1.

Low-voltage magnetoelectric coupling in membrane heterostructures.

Strain-mediated magnetoelectric (ME) coupling in ferroelectric (FE)/ferromagnetic (FM) heterostructures offers a unique opportunity for both fundamental scientific research and low-power multifunctional devices. Relaxor-FEs, such as (1 − )Pb(MgNb)O-()PbTiO (PMN-PT), are ideal FE layer candidates because of their giant piezoelectricity. However, thin films of PMN-PT suffer from substrate clamping, which substantially reduces piezoelectric in-plane strains.

Hot Electron Tunneling in Pt/LaAlO/SrTiO Heterostructures for Enhanced Photodetection.

LaAlO/SrTiO (LAO/STO) heterostructures, in which a highly mobile two-dimensional electron gas (2DEG) is formed, have great potential for optoelectronic applications. However, the inherently high density of the 2DEG hinders the observation of photo-excitation effects in oxide heterostructures. Herein, a strong photoresponse of the 2DEG in a Pt/LAO/STO heterostructure is achieved by adopting a vertical tunneling configuration.

Electronically reconfigurable complex oxide heterostructure freestanding membranes.

In recent years, lanthanum aluminate/strontium titanate (LAO/STO) heterointerfaces have been used to create a growing family of nanoelectronic devices based on nanoscale control of LAO/STO metal-to-insulator transition. The properties of these devices are wide-ranging, but they are restricted by nature of the underlying thick STO substrate. Here, single-crystal freestanding membranes based on LAO/STO heterostructures were fabricated, which can be directly integrated with other materials via van der Waals stacking.

Cooperative evolution of polar distortion and nonpolar rotation of oxygen octahedra in oxide heterostructures.

Polarity discontinuity across LaAlO/SrTiO (LAO/STO) heterostructures induces electronic reconstruction involving the formation of two-dimensional electron gas (2DEG) and structural distortions characterized by antiferrodistortive (AFD) rotation and ferroelectric (FE) distortion. We show that AFD and FE modes are cooperatively coupled in LAO/STO (111) heterostructures; they coexist below the critical thickness ( ) and disappear simultaneously above with the formation of 2DEG. Electron energy-loss spectroscopy and density functional theory (DFT) calculations provide direct evidence of oxygen vacancy ( ) formation at the LAO (111) surface, which acts as the source of 2DEG.

Engineered spin-orbit interactions in LaAlO/SrTiO-based 1D serpentine electron waveguides.

The quest to understand, design, and synthesize new forms of quantum matter guides much of contemporary research in condensed matter physics. One-dimensional (1D) electronic systems form the basis for some of the most interesting and exotic phases of quantum matter. Here, we describe a family of quasi-1D nanostructures, based on LaAlO/SrTiO electron waveguides, in which a sinusoidal transverse spatial modulation is imposed.

Gate-Tunable Optical Nonlinearities and Extinction in Graphene/LaAlO/SrTiO Nanostructures.

We explore the ultrafast optical response of graphene subjected to intense (∼10 V/cm) local (∼10 nm) electric fields. Nanoscale gating of graphene is achieved using a voltage-biased, SrTiO-based conductive nanowire junction "written" directly under the graphene and isolated from it by an insulating ultrathin (<2 nm) LaAlO barrier. Upon illumination with ultrafast visible-to-near-infrared (VIS-NIR) light pulses, the local field from the nanojunction creates a strong gate-tunable second-order nonlinearity in the graphene and produces a substantial difference-frequency (DFG) and sum-frequency generation (SFG) response detected by the nanojunction.

Electron-Lattice Coupling in Correlated Materials of Low Electron Occupancy.

In correlated materials including transition metal oxides, electronic properties and functionalities are modulated and enriched by couplings between the electron and lattice degrees of freedom. These couplings are controlled by external parameters such as chemical doping, pressure, magnetic and electric fields, and light irradiation. However, the electron-lattice coupling relies on orbital characters, i.

Oxygen Vacancy Linear Clustering in a Perovskite Oxide.

Oxygen vacancies have been implicitly assumed isolated ones, and understanding oxide materials possibly containing oxygen vacancies remains elusive within the scheme of the isolated vacancies, although the oxygen vacancies have been playing a decisive role in oxide materials. Here, we report the presence of oxygen vacancy linear clusters and their orientation along a specific crystallographic direction in SrTiO, a representative of a perovskite oxide. The presence of the linear clusters and associated electron localization was revealed by an electronic structure represented in the increase in the Ti valence state or corresponding Ti 3d electronic configuration along with divacancy cluster model analysis and transport measurement.

Effect of laser fluence on electrical properties of (Sr0.75,La0.25)TiO3 thin films grown by pulsed-laser-deposition.

We have grown Sr0.75La0.25TiO3 (SLTO) thin films using pulsed laser deposition (PLD) with various laser energy fluences.