arXiv subjects

Yingge Du

Publications and source records attributed to Yingge Du.

At least 19 recordsLinked to original sources

arXiv2026

High-Entropy A-Site Disorder Enhances Oxygen Evolution Reaction Activity and Stability in Nickelate Thin Films

Rare-earth nickelates are among the most active oxide electrocatalysts for the oxygen evolution reaction (OER), owing to their tunable Ni-O covalency, near-unity eg occupancy, and sensitivity to A-site chemistry, oxygen stoichiometry, and epitaxial strain. Here, we use epitaxial A-site high-entropy (La0.2Pr0.2Nd0.2Sm0.2Eu0.2)NiO3 thin films to reveal how epitaxial strain influences defect formation, Ni valence, electronic structure, and OER activity in a chemically disordered rare-earth (RE) sublattice. Tensile strain promotes Ruddlesden-Popper fault formation, interrupts the corner-sharing NiO6 network, and lowers the average Ni oxidation state. Although the occupied density of states near the Fermi level remains largely unchanged, O K-edge X-ray absorption spectroscopy reveals increased low-energy unoccupied states under tensile strain. First-principles calculations suggest that tensile strain shifts RE 4f-derived states toward the Fermi level, enhancing RE 4f-O 2p-Ni 3d hybridization. These coupled structural and electronic changes lead to earlier OER onset, stronger pre-catalytic Ni redox features, and higher activity than compressively strained films and representative single-A-site nickelates. The high-entropy nickelate also shows enhanced resistance to OER-induced structural degradation compared with LaNiO3. These results suggest that A-site configurational disorder and epitaxial strain can jointly tune defect formation and rare-earth-derived electronic states, providing a route for improving perovskite oxide electrocatalysts.

cond-mat.mtrl-sci↗

arXiv2026

Towards decoding the structure of water-magnetite interface

The molecular structure of water at iron-oxide interfaces is determined by the protonation state, orientation and population of interfacial OH species. These microscopic features can be decoded by combining surface-specific vibrational spectroscopy with reactive and accurate molecular dynamics simulations. In this way, it could be possible to connect the measured nonlinear optical response to specific molecular configurations at the magnetite-water interface, resolving the interfacial water structure. We investigated magnetite films in contact with liquid water at neutral and alkaline pH using phase-resolved sum-frequency generation (SFG) spectroscopy in the OH/OD stretching region and Fresnel correction of the optical response. In parallel, neural-network-potential molecular dynamics simulations were used to model the water-magnetite interface and identify interfacial water species, quantify their orientations, hydrogen-bonding environments and lifetimes, and compute species resolved SFG spectra. The combined analysis assigns distinct spectral features to dissociated surface OH groups, hydroxyls and water molecules adsorbed on octahedral iron sites, water bound at dissociation sites and water molecules above tetrahedral rows. The simulations reveal a reactive interfacial hydroxyl network with nanosecond-scale rearrangements and strong species-dependent hydrogen bonding. Experimentally, the SFG spectra show pronounced pH dependence, consistent with changes in surface charge and hydroxylation. A systematic difference between measured and computed SFG spectra indicates that the assumed surface model of magnetite does not fully represent the aqueous interface. This discrepancy provides a molecular constraint for improved models of magnetite-water interfaces and highlights SFG spectroscopy/ML-MD comparison as a valuable route to resolving oxide-water interfacial structures.

cond-mat.mtrl-sci↗

arXiv2026

Effect of Buried-Interface Preparation for Nb Superconducting Resonators on InP

Substrate surface preparation is a key step in the fabrication of electronic devices. In III--V semiconductor platforms, e.g. used in HEMTs and lasers, removal of the native substrate oxide is extremely important, where improper removal will negatively affect end-of-line device performance. However, the impact of substrate preparation in hybrid superconductor--semiconductor (S--Sm) systems relevant to quantum information applications remains poorly understood. This study compares three surface preparations for the deposition of sputtered Nb films on InP: (i) no intentional oxide removal (control), (ii) \textit{in-situ} $\mathrm{Ar}^{+}$ milling, and (iii) S-passivation. \textit{In-situ} $\mathrm{Ar}^{+}$ milling reduces the O concentration at the metal--substrate (MS) interface, but also roughens the InP surface, increasing the effective thickness of the Nb--InP interface and promoting O incorporation through extended defects in the Nb film. S-passivation suppresses interfacial O more effectively while preserving a sharper and smoother buried interface. It also yields Nb films with higher superconducting transition temperatures and less structural damage than the $\mathrm{Ar}^{+}$-milled samples. Despite these materials improvements, the microwave response is comparable across the three preparations. At single photon powers, the highest internal quality factors, $Q_i$, are approximately $1.30\times10^{5}$ ($130\mathrm{k}$) for the control resonators, $9.7\times10^{4}$ ($97\mathrm{k}$) for the S-passivated resonators, and $8.4\times10^{4}$ ($84\mathrm{k}$) for the $\mathrm{Ar}^{+}$-milled resonators. These results suggest that the present devices are not primarily limited by dielectric loss at the buried Nb--InP interface.

cond-mat.mes-hall↗

arXiv2026

Multimode magnon-phonon cavity driven by symmetry-locked strain fields

Hybrid magnon-phonon cavities with precise control knobs are highly sought after for coherent energy and signal transduction in solid-state platforms. While strain offers a powerful means to tune magnonic characteristics, extending strain engineering into magnon-phonon hybridization has remained elusive. Moreover, implementing controllable strain at the meso- or nanoscale poses a formidable challenge, as spatial inhomogeneity of strain fields often leads to enhanced damping and reduced coherence, thereby hindering device integration and scalability. Here, we present an epitaxial La0.7Sr0.3MnO3/SrTiO3 (LSMO/STO) heterostructure that exhibits strong coupling between the Kittel magnon and acoustic phonon. Leveraging the emergence of structural domains when STO undergoes a cubic-to-tetragonal phase transition, we create anisotropic local strains at the interface. Remarkably, the anisotropic local strain of less than 0.1 % drives the pronounced splitting of the magnon into three branches. Each branch independently hybridizes with acoustic phonons, forming a matrix of magnon-phonon avoided crossings that underpins multimode transduction and programmable networks in frequency and magnetic field space. An analytical model reveals that the split magnon branches are deterministically locked to the three main crystalline axes, enabling robust, orientation-selective control of the hybridized magnon-phonon spectrum against spatial inhomogeneity. Our results establish designed local strain as an exceptionally sensitive trigger for multimode magnon-phonon hybridization in magnetoelastic oxide heterostructures, and highlight local strain engineering as a viable strategy for designing tunable hybrid magnonic and phononic devices.

cond-mat.mtrl-sci↗

arXiv2026

Isotopically enriched epitaxial CaWO$_{4}$ thin films for Er$^{3+}$ spin-photon quantum interfaces

Rare earth ion (REI)-doped oxide thin films are attractive for the application of quantum interconnects due to their stable optical levels and scalability$^{1-3}$. Among them, Er$^{3+}$ doped CaWO$_{4}$ is promising because it possesses narrow optical linewidth transitions and a long spin coherence time$^{4-6}$. The electron spin coherence is limited at high temperatures by paramagnetic impurities and by the presence of the 14.3% $^{183}$W nuclear spin. To further increase the spin coherence time at millikelvin temperatures, where the paramagnetic impurities are frozen out, our approach is to synthesize chemically and isotopically purified thin films as a host material. We first grow non-isotopically enriched Er$^{3+}$ doped CaWO$_{4}$ thin films, which exhibit a 214(13) MHz photoluminescence (PL) inhomogeneous linewidth, indicating the thin film has high crystalline quality. We then grow isotopically enriched CaWO$_{4}$ thin films using an isotopically purified $^{186}$WO$_{3}$ source. Time of flight secondary ion mass spectrometry (ToF-SIMS) was used to measure the relative concentration of W isotopes. $^{183}$W, the only W isotope that has a net nuclear spin and is the major cause of spin decoherence, was at a relative abundance of 1.2%, a factor of 10 lower than natural abundance. We also observed PL emission from single ions after integrating nano-photonic devices with the thin film. These results establish isotopically engineered CaWO$_{4}$ thin films as a promising platform for future studies of nuclear-spin-limited coherence and for scalable rare-earth-ion-based quantum nanophotonic devices.

quant-ph↗

arXiv2026

Tantalum Damascene Coplanar Waveguide Resonators Fabricated Using 300 mm Scale Processes

Surface oxides contribute to losses in superconducting transmon devices resulting in degraded performance. We explore the use of the damascene process to replace the sidewall native oxide of a device with a metal/substrate interface. We simulate sidewall oxidation by burying an oxide layer during fabrication. We observe a modest improvement between the two types of devices, which is suggestive of a reduction in the surface participation ratio.

quant-ph↗

arXiv2025

Selective Oxidation and Cr Segregation in High-Entropy Oxide Thin Films

High-entropy oxides (HEOs) offer exceptional compositional flexibility and structural stability, making them promising materials for energy and catalytic applications. Here, we investigate Sr doping effects on B-site cation oxidation states, local composition, and structure in epitaxial La1-xSrx(Cr0.2Mn0.2Fe0.2Co0.2Ni0.2)O3 thin films. X-ray spectroscopies reveal that Sr doping preferentially promotes Cr oxidation from Cr3+ to Cr6+, partially oxidizes Co and Ni, while leaving Mn4+ and Fe3+ unchanged. Atomic-resolution scanning transmission electron microscopy with energy-dispersive X-ray spectroscopy shows pronounced Cr segregation, with Cr exhibiting depletion at the film-substrate interface and enrichment at the film surface, along with the formation of a partially amorphous phase in heavily Sr-doped samples. This segregation is likely driven by oxidation-induced migration of smaller, high-valence Cr cations during the growth. These findings underscore the critical interplay between charge transfer, local strain, and compositional fluctuations, providing strategies to control surface composition and electronic structure in HEOs for more robust electrocatalyst design.

cond-mat.mtrl-sci↗

arXiv2024

Revealing the Evolution of Order in Materials Microstructures Using Multi-Modal Computer Vision

The development of high-performance materials for microelectronics, energy storage, and extreme environments depends on our ability to describe and direct property-defining microstructural order. Our present understanding is typically derived from laborious manual analysis of imaging and spectroscopy data, which is difficult to scale, challenging to reproduce, and lacks the ability to reveal latent associations needed for mechanistic models. Here, we demonstrate a multi-modal machine learning (ML) approach to describe order from electron microscopy analysis of the complex oxide La$_{1-x}$Sr$_x$FeO$_3$. We construct a hybrid pipeline based on fully and semi-supervised classification, allowing us to evaluate both the characteristics of each data modality and the value each modality adds to the ensemble. We observe distinct differences in the performance of uni- and multi-modal models, from which we draw general lessons in describing crystal order using computer vision.

cond-mat.mtrl-sci↗

arXiv2024

Tetragonal BaCoO$_3$: A Co$^{4+}$ Ferromagnetic Mott Insulator with Inverted Spin Crossover

The interplay between crystal electric field splitting of d states and Hund's rule exchange energy in cobalt-based perovskites offers a promising avenue for inducing spin-state transitions. This study reports a new body-centered tetragonal (BCT) phase of BaCoO$_3$ (BCT-BaCoO$_3$), synthesized under high pressure (15 GPa) and high temperature (1200 °C) conditions. BCT-BaCoO$_3$ adopts a double perovskite structure of EuTiO$_3$-type (space group I4/mcm, #140), confirmed by high-resolution scanning transmission electron microscopy. X-ray photoelectron spectroscopy reveals a rare Co$^{4+}$ valence state. Magnetization and X-ray absorption measurements reveal a low-spin to high-spin transition that takes place between 200 and 300 K. While spin crossovers are relatively common among common oxides, the one observed in BCT-BaCoO$_3$ is remarkable in that it proceeds in the opposite direction from conventional spin transitions. BCT-BaCoO$_3$ exhibits a low-spin (S = 1/2) state at high temperatures and transitions to a high-spin (S = 5/2) state at low temperatures. Within the high-spin state, hard ferromagnetic order onsets at T$_C$ = 107 K. Electrical resistivity indicates weak magnetoresistance and insulating behavior. Overall, BCT-BaCoO$_3$ presents an exceptional model for the exploration of spin-state transitions and the study of Co spin states in cobalt-based perovskites.

cond-mat.mtrl-sci↗

arXiv2024

Tunable Collective Excitations in Epitaxial Perovskite Nickelates

The formation of plasmons through the collective excitation of charge density has generated intense discussions, offering insights to fundamental sciences and potential applications. While the underlying physical principles have been well-established, the effects of many-body interactions and orbital hybridization on plasmonic dynamics remain understudied. In this work, we present the observation of conventional metallic and correlated plasmons in epitaxial La1-xSrxNiO3 (LSNO) films with varying Sr doping concentrations (x = 0, 0.125, 0.25), unveiling their intriguing evolution. Unlike samples at other doping concentrations, the x = 0.125 intermediate doping sample does not exhibit the correlated plasmons despite showing high optical conductivity. Through a comprehensive experimental investigation using spectroscopic ellipsometry and X-ray absorption spectroscopy, the O2p-Ni3d orbital hybridization for LSNO with a doping concentration of x = 0.125 is found to be significantly enhanced, alongside a considerable weakening of its effective correlation U*. These factors account for the absence of correlated plasmons and the high optical conductivity observed in LSNO (0.125). Our results underscore the profound impact of orbital hybridization on the electronic structure and the formation of plasmon in strongly-correlated systems. This in turn suggest that LSNO could serve as a promising alternative material in optoelectronic devices.

cond-mat.mtrl-sci↗

arXiv2024

Uncovering an Interfacial Band Resulting from Orbital Hybridization in Nickelate Heterostructures

The interaction of atomic orbitals at the interface of perovskite oxide heterostructures has been investigated for its profound impact on the band structures and electronic properties, giving rise to unique electronic states and a variety of tunable functionalities. In this study, we conducted an extensive investigation of the optical and electronic properties of epitaxial NdNiO3 thin films grown on a series of single crystal substrates. Unlike films synthesized on other substrates, NdNiO3 on SrTiO3 (NNO/STO) gives rise to a unique band structure which features an additional unoccupied band situated above the Fermi level. Our comprehensive investigation, which incorporated a wide array of experimental techniques and density functional theory calculations, revealed that the emergence of the interfacial band structure is primarily driven by the orbital hybridization between Ti 3d orbitals of the STO substrate and O 2p orbitals of the NNO thin film. Furthermore, exciton peaks have been detected in the optical spectra of the NNO/STO film, attributable to the pronounced electron-electron (e-e) and electron-hole (e-h) interactions propagating from the STO substrate into the NNO film. These findings underscore the substantial influence of interfacial orbital hybridization on the electronic structure of oxide thin-films, thereby offering key insights into tuning their interfacial properties.

cond-mat.mtrl-sci↗

arXiv2023

Metal-to-insulator transition in oxide semimetals by anion doping

Oxide semimetals exhibiting both nontrivial topological characteristics stand as exemplary parent compounds and multiple degrees of freedom, offering great promise for the realization of novel electronic states. In this study, we present compelling evidence of profound structural and transport phase shifts in a recently uncovered oxide semimetal, SrNbO3, achieved through effective in-situ anion doping. Notably, a remarkable increase in resistivity of more than three orders of magnitude at room temperature is observed upon nitrogen-doping. The extent of electronic modulation in SrNbO3 is strongly correlated with the misfit strain, underscoring its phase instability to both chemical doping and crystallographic symmetry variations. Using first-principles calculations, we discern that elevating the level of nitrogen doping induces an upward shift in the conductive bands of SrNbO3-dNd. Consequently, a transition from a metallic state to an insulating state becomes apparent as the nitrogen concentration reaches a threshold of 1/3. This investigation sheds light on the potential of anion engineering in oxide semimetals, offering pathways for manipulating their physical properties. These insights hold promise for future applications that harness these materials for tailored functionalities.

cond-mat.mtrl-sci↗

arXiv2023

Unsupervised segmentation of irradiation$\unicode{x2010}$induced order$\unicode{x2010}$disorder phase transitions in electron microscopy

We present a method for the unsupervised segmentation of electron microscopy images, which are powerful descriptors of materials and chemical systems. Images are oversegmented into overlapping chips, and similarity graphs are generated from embeddings extracted from a domain$\unicode{x2010}$pretrained convolutional neural network (CNN). The Louvain method for community detection is then applied to perform segmentation. The graph representation provides an intuitive way of presenting the relationship between chips and communities. We demonstrate our method to track irradiation$\unicode{x2010}$induced amorphous fronts in thin films used for catalysis and electronics. This method has potential for "on$\unicode{x2010}$the$\unicode{x2010}$fly" segmentation to guide emerging automated electron microscopes.

cond-mat.mtrl-sci↗

arXiv2023

Direct and in situ examination of Li+ transport kinetics in isotope labelled solid electrolyte interphase

Here, using unique in-situ liquid secondary ion mass spectroscopy on isotope-labelled solid-electrolyte-interphase (SEI), assisted by cryogenic transmission electron microscopy and constrained ab initio molecular dynamics simulation, for the first time we answer the question regarding Li+ transport mechanism across SEI, and quantitatively determine the Li+-mobility therein. We unequivocally unveil that Li+ transport in SEI follows a mechanism of successive displacement, rather than "direct-hopping". We further reveal, in accordance with spatial-dependence of SEI structure across the thickness, the apparent Li+ self-diffusivity varies from 6.7*10-19 m2/s to 1.0*10-20 m2/s, setting a quantitative gauging of ionic transport behavior of SEI layer against the underlining electrode as well as the rate limiting step of battery operation. This direct study on Li+ kinetics in SEI fills part of the decade-long knowledge gap about the most important component in advanced batteries and provides more precise guidelines to the tailoring of interphasial chemistries for future battery chemistries.

cond-mat.mtrl-sci↗

arXiv2022

Resolving diverse oxygen transport pathways across Sr-doped lanthanum ferrite and metal-perovskite heterostructures

Perovskite structured transition metal oxides are important technological materials for catalysis and solid oxide fuel cell applications. Their functionality often depends on oxygen diffusivity and mobility through complex oxide heterostructures, which can be significantly impacted by structural and chemical modifications, such as doping. Further, when utilized within electrochemical cells, interfacial reactions with other components (e.g. Ni- and Cr-based alloy electrodes and interconnects) can influence the perovskite's reactivity and ion transport, leading to complex dependencies that are difficult to control in real-world environments. Here we use isotopic tracers and atom probe tomography to directly visualize oxygen diffusion and transport pathways across perovskite and metal-perovskite heterostructures, i.e. (Ni-Cr coated) Sr-doped lanthanum ferrite (LSFO). Annealing in 18O2(g) results in elemental and isotopic redistributions through oxygen exchange (OE) in the LSFO while Ni-Cr undergoes oxidation via multiple mechanisms and transport pathways. Complementary density functional theory (DFT) calculations at experimental conditions provide rationale for OE reaction mechanisms and reveal a complex interplay of different thermodynamic and kinetic drivers. Our results shed light on the fundamental coupling of defects and oxygen transport in an important class of catalytic materials.

cond-mat.mtrl-sci↗

arXiv2021

Tuning magnetic and optical properties through strain in epitaxial LaCrO3 thin films

We report on the effect of epitaxial strain on magnetic and optical properties of perovskite LaCrO3 (LCO) single crystal thin films. Epitaxial LCO thin films are grown by pulsed laser deposition on proper choice of substrates to impose different strain states. A combined experimental and theoretical approach is used to demonstrate the direct correlation between lattice-strain and functional properties. The magnetization results show that the lattice anisotropy plays a critical role in controlling the magnetic behavior of LCO films. The strain induced tetragonality in the film lattice strongly affects the optical transitions and charge transfer gap in LCO. This study opens new possibilities to tailoring the functional properties of LCO and related materials by strain engineering in epitaxial growth.

cond-mat.mtrl-sci↗

arXiv2018

Hole-Induced Electronic and Optical Transitions in La1-xSrxFeO3 Epitaxial Thin Films

We have investigated the electronic and optical properties of epitaxial La1-xSrxFeO3 for x from 0 to 1 prepared by molecular beam epitaxy. Core-level and valence-band x-ray photoemission features monotonically shift to lower binding energy with increasing x, indicating downward movement of the Fermi level toward to the valence band maximum. Both Fe 2p and O 1s spectra broaden to higher binding energy with increasing x, consistent with delocalization of Sr-induced holes in the Fe 3d/O 2p hybridized valence band. Combining X-ray valence band photoemission and O K-edge x-ray absorption data, we map the evolution of the occupied and unoccupied bands and observe a narrowing of the gap, along with a transfer of state density from just below to just above the Fermi level, resulting from hole doping. In-plane transport measurements confirm that the material becomes a p-type semiconductor at lower doping levels and exhibits a insulator-to-metal transition at x equal to 1. Sub-gap optical transitions revealed by spectroscopic ellipsometry are explained based on insight from theoretical densities of states and first-principles calculations of optical absorption spectra.

cond-mat.mtrl-sci↗

arXiv2018

The Onset of Phase Separation in the Double Perovskite Oxide La$_2$MnNiO$_6$

Identification of kinetic and thermodynamic factors that control crystal nucleation and growth represents a central challenge in materials synthesis. Here we report that apparently defect-free growth of La$_2$MnNiO$_6$ (LMNO) thin films supported on SrTiO$_3$ (STO) proceeds up to $1-5$ nm, after which it is disrupted by precipitation of NiO phases. Local geometric phase analysis and ensemble-averaged X-ray reciprocal space mapping show no change in the film strain away from the interface, indicating that mechanisms other than strain relaxation induce the formation of the NiO phases. $Ab \, initio$ simulations suggest that oxygen vacancies become more likely with increasing thickness, due to the electrostatic potential build-up associated with the polarity mismatch at the film-substrate interface, this, in turn, promotes the formation of Ni-rich regions. These results suggest that the precipitate-free region could be extended further by increasing the oxygen chemical potential through the use of an elevated oxygen pressure or by incorporating electron redistributing dopants to suppress the built-in potential.

cond-mat.mtrl-sci↗