High-temperature superconducting (HTS) YBa2 Cu(3)0(7-delta) (YBCO) thin films and Josephson junctions are pivotal for both fundamental research into HTS mechanisms and practical electronic devices operating at liquid nitrogen temperatures. This article provides a comprehensive review of recent advances in the fabrication techniques, physical properties, and applications status of YBCO thin films and Josephson junctions, describing the path from fundamental research toward technological implementation. Substantial progress has been made in the growth of YBCO thin films. Advanced deposition methods, including pulsed laser deposition (PLD), magnetron sputtering, and metal-organic chemical vapor deposition (MOCVD), have enabled the production of films, with enhanced superconducting properties over large areas. Critical parameters such as the superconducting transition temperature (Ic). critical current density (J), and surface smoothness have seen continuous improvement. Through strategies such as substrate strain, the use of buffer layers (e.g., CeO2), the construction of superlattices (e.g., PrBa2 Cu(3)0(7)/YBCO), and annealing with active oxygen sources, researchers can effectively suppress twinning rate, control oxygen doping homogeneity, and modulate electronic structures. These capabilities are indispensable not only for probing fundamental phenomena like the pseudogap phase and charge density waves but also for meeting the exacting material specifications required for high-performance devices. Nevertheless, challenges persist. The microwave surface resistance (R-3) of even the best films, while far superior to conventional metals, has not yet reached its theoretical minimum. Great achievements have been realized in the fabrication of YBCO Josephson junctions, the fundamental building blocks of HTS electronics. Superconducting quantum interference filters (SQIFs), comprising arrays of junctions, exhibiting an improved range of single-valued and linear range of the magnetic field-voltage response, enable highly sensitive absolute magnetometry. The high-temperature superconducting terahertz mixer utilizes the nonlinear current-voltage characteristics of the Josephson junction to achieve frequency conversion of microwave/terahertz signals. Compared to other types, it has the potential for lower noise temperature and a lighter cooling system. Series arrays of thousands of junctions are also being developed for a voltage standard through alternating current Josephson effect. Furthermore, the phase-sensitive technique of YBCO untwinned thin films and Josephson junctions provides crucial evidence for revealing the pairing symmetry of HTS materials. The community has developed a variety of methods for preparing Josephson junctions, and each technique has its own unique characteristics. Bi-crystal junctions, defined by a grain boundary on a specially prepared substrate, offer a relatively simple and reproducible structure. Step-edge junctions, created by depositing YBCO over a lithographically defined substrate step, provide good design flexibility for individual devices. A step-edge SNS junction is formed by depositing metal on the steeper steps, as the junction region contracts with grain boundaries. Inclined-edge junctions have excellent stability and anti-interference capabilities with top electrodes. In particular, the emergence of focused helium ion beam (He-FIB) technology represents a breakthrough. This direct-write technique with a high degree of freedom utilizes a sub-nanometer helium ion probe to locally modify the oxygen content or crystal structure, creating a tunable barrier within the range limited by the superconducting coherence length. Its greatest strength lies in endoling the fabrication of large-scale, dense arrays of junctions with complex geometries, a capability important for integrated devices. Despite these promising developments, critical challenges should be addressed to achieve industrialization and commercialization. For junction arrays, the statistical scatters in key parameters like critical current (I-e) and normal resistance (R-a) need further optimization for device stability and reproducibility. Future progress depends on a co-optimization strategy: advancing film growth to achieve outstanding and homogeneous superconducting performance and perfect surface flatness; minimizing damage and improving uniformity in nanofabrication processes of junctions; establishing microstructure-function relationships to guide empirical optimization with physical insight

Controlled generation of topological spin textures, such as merons and their bound state, the bimerons, is essential for advancing spintronic technologies and elucidating soliton physics in condensed matter. Using in situ Lorentz transmission electron microscopy coupled with femtosecond laser pulse, we demonstrate the creation of two distinct Bloch-type bimeron states in chiral magnet Co8Zn8Mn4 thin plates at room temperature. Magnetic imaging and micromagnetic simulations reveal that bimeron density varies with applied magnetic field strength, enabling dynamic topological control. We further establish that the topological classification of laser-generated bimerons is invariant with specimen thickness. Field-driven reversible transformations between elongated and circular bimeron morphologies are observed, governed by the competition of Zeeman energy and magnetic shape anisotropy. Micromagnetic simulations quantitatively reproduce these metastable states, validating a unified meron-skyrmion topological framework. This work establishes a single-pulse protocol for optical manipulation of topological spin textures.

Topological insulators host exotic quantum phenomena such as the quantum spin Hall (QSH) effect, which enables dissipationless one-dimensional edge conduction. Realizing such states at room temperature and on a macroscopic scale is essential for energy-efficient electronics and quantum technologies, yet remains a fundamental challenge due to material limitations. Here, using microwave impedance microscopy, we directly visualize robust QSH states persisting up to 300 K in α-Bi4Br4 nanowires. This stability and scalability are enabled by a stair stepped stacking configuration, a multilayer geometry in which QSH edge states from individual layers remain spatially decoupled. This configuration circumvents the stringent alignment and layer number constraints of previous proposals, allowing robust stair-stepped QSH (SS-QSH) conduction in structures several micrometers long and hundreds of nanometers high. Magnetic field and temperature dependent measurements confirm their intrinsic topological nature. Crucially, the SS-QSH and bulk signals scale with nanowire height, verifying the stair stepped origin. Our results are also successfully reproduced by finite-element analysis simulations. This work establishes α Bi4Br4 as a practical platform for high temperature topological electronics and demonstrates a generalizable stacking strategy for designing scalable QSH systems.

Fe-based superconductors have attracted much attention. Among them, FeTe is unique in the series of FeSe 1- x Te x with absence of superconductivity. Interestingly, Fe 1+ y Te thin film shows superconductivity after oxygen annealing, and the mechanism is still elusive. This study investigates structural, superconducting, and magnetic properties of a series of Fe 1+ y Te thin films (FeTe:O x ) annealed under different oxygen partial pressures. Scanning transmission electron microscopy is used to examine the amount and distribution of excess Fe, the migration of excess Fe toward the film surface, and the structure and distribution of the iron oxide layer formed on the film surface. Exchange bias emerges at the interface between the ferromagnetic iron oxide and FeTe:O x , persisting in the superconducting state. Theoretical calculations suggest the occurrence of both interstitial oxygen and substitutional oxygen, and suppression of AFM order by the former, which can account for superconductivity. This work is helpful for understanding the interaction of oxygen with Fe 1+ y Te and mechanism of superconductivity for FeTe:O x thin films.

Distinguishing surface recombination from subsurface transport is vital for optoelectronics but remains challenging in scanning ultrafast electron microscopy (SUEM) because of signal convolution. Here, we demonstrate that the detector bias (Vf) enables effective depth-selective probing to spatially disentangle these competing dynamics within the near-surface region. Experiments on p-type silicon reveal a striking voltage-tunable contrast inversion, marking a transition from surface-dominated to subsurface-dominated regimes. We attribute this to a mechanistic competition between surface potential restoration governing collection and subsurface band flattening modulating emission. Multiphysics simulations confirm this framework by linking depth-dependent charge distributions to contrast evolution. We thus achieve independent visualization of spatially entangled processes, specifically isolating surface trapping from subsurface diffusion and providing a physical basis for resolving vertical carrier stratification.

The ultrafast transmission electron microscope (UTEM) provides a powerful platform for characterizing ultrafast laser-induced structural dynamics in functional materials. In this article, the ultrafast structural dynamics of silver nanowires (Ag NWs) were investigated using electron diffraction in UTEM. Both the diffraction intensity and Bragg peak shift from picosecond to microsecond scales were analyzed to track the full-cycle structural dynamics after laser excitation. The evolution of the diffraction intensity and the shift of Bragg peaks in various directions on the picosecond to nanosecond timescales have unveiled anisotropic atomic disorder and lattice expansion along the radial and axial directions. These anisotropic lattice responses are attributed to the unique one-dimensional structure of Ag NWs, which facilitates the subsequent energy transfer from the radial to the axial direction on the nanosecond timescale. The anisotropic lattice responses were corroborated by comparing them with the isotropic results obtained from a polycrystalline silver film. Additionally, we observed breathing and extension modes in the radial and axial directions, respectively. A two-step electron-phonon coupling process due to the trapping of hot electrons by surface oxidation states and recovery dynamics was also reported. Our findings elucidate the ultrafast lattice dynamics of Ag NWs across the picosecond to microsecond scale, thus laying the groundwork for their practical applications.

The insulator-to-metal transition (IMT) in strongly correlated materials, such as vanadium dioxide (VO2), offers a transformative platform for next-generation adaptive electronics and neuromorphic computing. However, harnessing this non-equilibrium phase transition for deterministic device operation is fundamentally hindered by the inability to disentangle electric-field effects from Joule heating, owing to a lack of operando techniques capable of resolving phase dynamics at nanoscale spatial and sub-nanosecond temporal scales. Here, using a newly developed electrical-pulse-pump ultrafast transmission electron microscope (E-UTEM), we directly visualize the multi-scale electro-thermo-mechanical dynamics of the IMT in suspended VO2 devices. Our results reveal that electric-field-induced Poole-Frenkel (PF) emission, localized by patterned oxygen vacancies, plays a decisive role in redistributing the internal electric field to trigger a deterministic Mott transition. The extreme non-linearity of this PF effect enables the formation of dynamically reconfigurable connectivity topologies that bypass conventional thermal limits. Furthermore, we observe that the coupling of thermal and elastic energies governs a discrete domain evolution, characterized by step-wise and period-doubling configurational resets, which is a hallmark of non-equilibrium phase dynamics in constrained geometries. By integrating experimental imaging with phase-field simulations, we establish a comprehensive framework for the electrically-driven IMT and predict sub-100-ps switching kinetics. These findings provide a fundamental basis for the rational design of ultrafast, low-energy functional devices through nanoscale defect and strain engineering in correlated systems.

Hopfions are three-dimensional (3D) topological solitons predicted to exist in diverse magnetic systems, yet their practical utility has been largely restricted to cryogenic environments. Here, we overcome this temperature constraint by demonstrating stable magnetic hopfions in the chiral magnet Co8Zn8Mn4 at and above room temperature. Using a transmission electron microscope equipped for in situ optical excitation, we generate magnetic hopfions with femtosecond laser pulses. Long-term observations further reveal Brownian-like motion at room temperature and thermally activated collapse upon approaching the high-temperature regime. Together with micromagnetic simulations and homotopy group analysis, our experimental observations uncover the hopfion formation mechanism through the fusion of bimeron pairs. These findings establish room-temperature magnetic hopfions and provide a framework for their further studies under technologically relevant conditions.

A comprehensive investigation of the superconducting response to disruptions is essential for elucidating the mechanisms underlying performance enhancement. Here, we systematically study the effects of Xe-ion irradiation in BaHfO3-doped EuBa2Cu3O7−δ films. Our results show that irradiation significantly modifies intrinsic superconducting parameters. Analysis of critical current density Jc and pinning energy reveals that the degradation of intrinsic properties is a primary factor driving performance decline, and we highlight that enhancing depairing current density Jd is more effective than defect engineering alone, particularly within the quantum critical region. Raman spectroscopy indicates that the degradation arises from disorder at the chain oxygen sites. These findings emphasize that a thorough understanding of both intrinsic superconducting properties and extrinsic pinning structures is critical for optimizing high-temperature superconductor performance.

Fe‐based superconductors have attracted much attention. Among them, FeTe is unique in the series of FeSe 1‐ x Te x with absence of superconductivity. Interestingly, Fe 1+ y Te thin film shows superconductivity after oxygen annealing, and the mechanism is still elusive. This study investigates structural, superconducting, and magnetic properties of a series of Fe 1+ y Te thin films (FeTe:O x ) annealed under different oxygen partial pressures. Scanning transmission electron microscopy is used to examine the amount and distribution of excess Fe, the migration of excess Fe toward the film surface, and the structure and distribution of the iron oxide layer formed on the film surface. Exchange bias emerges at the interface between the ferromagnetic iron oxide and FeTe:O x , persisting in the superconducting state. Theoretical calculations suggest the occurrence of both interstitial oxygen and substitutional oxygen, and suppression of AFM order by the former, which can account for superconductivity. This work is helpful for understanding the interaction of oxygen with Fe 1+ y Te and mechanism of superconductivity for FeTe:O x thin films.

Time-resolved visualization of local structural dynamics driven by external fields is essential for understanding structure–property relationships in functional materials and devices. Conventional ultrafast methods primarily capture femtosecond-to-picosecond photoinduced dynamics, yet they lack real-space access to spatially inhomogeneous processes occurring at their intrinsic mesoscopic timescales that govern material and device performance—particularly electrically driven processes that closely mimic actual device operating conditions. Here, we report a multifunctional ultrafast transmission electron microscopy (UTEM) platform targeting reversible structural dynamics spanning nanoseconds to microseconds under stroboscopic multi-field excitation. Our system employs photoelectron pulses generated by nanosecond UV laser illumination as the probe, alongside optical and electric pulses as pump excitation. A unified electronic synchronization scheme based on a high-speed photodiode and a digital delay generator enables precise timing control among the optical pump, electrical pump, and photoelectron pulses across the nanosecond-to-microsecond range. Using vanadium dioxide (VO2) as a model system, we demonstrate a combined spatiotemporal resolution with measurable signals on the order of 10 nm–10 ns, allowing real-space mapping of spatially inhomogeneous dynamics. Electrical-pump experiments further reveal Joule-heating-induced non-uniform structural phase transitions and thermal-shock-excited megahertz-range mechanical oscillations. These results establish the developed multi-field UTEM platform as a practical tool for probing local structural dynamics in functional materials under optical and electrical excitation.

To address the limitations in temporal resolution of an ultrafast electron microscope (UEM) and the shortcomings of existing pulsed-electron characterization methods, we introduce a fast, energy-filter-free technique for measuring electron pulse duration that exploits the interaction between free electrons and the phase-matched near-field of a periodic grating. The interaction induces a measurable transverse broadening of the electron beam, which directly encodes the temporal profile of the electron pulse. Implementing this method on a Wehnelt-controlled UEM, we observe an asymmetric temporal distribution with a long trailing edge at high bias voltage. Finite-element simulations of electron trajectories replicate the experimental trends and identify the temporal aberration of the electrostatic lens as the primary cause of asymmetric broadening. This approach enables rapid, high-precision diagnostics of electron-pulse characteristics without requiring an energy-filter spectrometer, and the findings provide valuable insights into the factors that presently limit UEM temporal resolution.

The pursuit of high-speed, low-power spintronic devices has driven extensive research into the anomalous Hall effect (AHE) in antiferromagnets. Concurrently, the topological Hall effect (THE), a hallmark of chiral spin textures, has emerged as a critical probe of nontrivial magnetism. Here, we report the synthesis and physical properties of V1/4NbSe2, a centrosymmetric van der Waals antiferromagnet with a 2 & times; 2 superlattice structure. It exhibits two successive antiferromagnetic (AFM) transitions: aparamagnetic-to-AFM1 transition at TN = 14.7 K, followed by an AFM1-to-AFM2 transition below Tt approximate to 6.4 K. Magnetic characterization reveals dominant AFM interactions, weak magnetocrystalline anisotropy, and nonlinear magnetization suggestive of a spin-flop-like transition. Electrical transport demonstrates coexisting AHE and THE phenomena. The AHE, which is likely dominated by the intrinsic mechanism, peaks near TN with a conductivity of similar to 160 Q-1cm-1. Notably, the THE emerges exclusively within the AFM2 phase, suggesting its origin of a field-induced nonzero scalar spin chirality. Magnetoresistance exhibits butterfly-shaped hysteresis loops stemming from spin-dependent electron scattering. These phenomena collectively point to an intricate magnetic ground state in the absence of Dzyaloshinskii-Moriya interaction, warranting further investigation to unravel the underlying spin configuration.

Topological defects play a central role in spontaneous symmetry breaking, profoundly influencing the order parameter and emergent states. These effects are particularly complex in low-dimensional systems with strong electronic correlations and dimensional crossovers, necessitating detailed and sophisticated analyses. Using CuTe as a prototype, with charge density wave (CDW) states near room temperature (Tc = 335 K), this study reveals a novel CDW induced by topological defects, specifically CDW dislocations. Temperature-dependent transmission electron microscopy was employed to visualize the emergence of this novel CDW at topological singularities, where the amplitude is significantly suppressed. The formation and melting of this CDW exhibit an unconventional, temperature-dependent hysteresis near Tc, which is further corroborated by clearly observed anomalous hysteresis in electrical transport. This work offers a comprehensive picture of emergent CDW states in CuTe and paves the way for the potential application of CDW systems in information storage technologies.

Abstract Layered topological insulators such as Bi 2 Se 3 exhibit rich phonon dynamics, which are crucial for understanding their thermal transport mechanisms and electronic properties. In this work, we investigate the multiscale nonequilibrium lattice dynamics in Bi 2 Se 3 thin films using ultrafast transmission electron microscopy (UTEM). By exploiting the complementarity between real-space ultrafast electron microscopy (UEM) and ultrafast electron diffraction (UED), we show that the characteristic frequencies of the lattice dynamics are consistent in real and reciprocal space. This cross-validation supports the interpretation that the transient anti-phase oscillation of Friedel diffraction pairs originates from reciprocal-space geometric evolution induced by the breathing mode: under large-angle tilting, reciprocal rods with nonzero out-ofplane Miller indices undergo periodic stretching and displacement along the c * axis, thereby asymmetrically changing their intersections with the Ewald sphere. This process corresponds directly to the coherent motion of lattice bend contours observed in real space. The study further reveals that phonon propagation exhibits pronounced scale dependence. On the picosecond timescale, the dynamics are dominated by a longitudinal standing-wave breathing mode confined by the film thickness, with the oscillation frequency following an inverse dependence on film thickness. Under the [001] zone-axis condition, defect-mediated in-plane traveling waves propagating at the speed of sound are observed. Furthermore, on the nanosecond timescale, the suspended thin film exhibits mechanical resonance with a high quality factor, accompanied by a rich spectrum of higher-order harmonics. These findings provide direct visual evidence for the multilevel dynamical responses of coherent phonons under the same pump excitation, manifesting at different timescales and boundary conditions from the gigahertz (GHz) to megahertz (MHz) regime, highlighting the potential of Bi 2 Se 3 for high-frequency nanomechanical applications.

Magnetic flux profoundly influences the phase factor of charge particles, leading to exotic quantum phenomena. A recent example is that the orbital effect of magnetic field could induce finite-momentum pairing state in nanoflakes, which offers a new pathway to realize the spatially modulated superconductivity distinct from the Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) state induced by Zeeman effect. However, whether such intriguing state can exist in the bulk materials under extremely large magnetic field remains elusive. Here we report the orbital effect induced finite-momentum pairing state with exceedingly large in-plane critical field in a bulk superconducting superlattice. Remarkably, the in-plane critical field shows a pronounced upturn behavior, exceeding eight times the Pauli limit which is comparable to monolayer Ising superconductor. Under high in-plane magnetic fields, significant anisotropic transport behavior between the interlayer and intralayer directions is detected, highlighting the critical role of suppressed interlayer coherence in the orbital effect induced finite-momentum pairing state. Crucially, this finite-momentum pairing state remains robust against moderate disorder. Our findings suggest that van der Waals superlattices, with strong Ising spin-orbit coupling and tunable interlayer coherence, offer new avenues for constructing and modulating unconventional superconducting states.

Exploring advanced techniques capable of probing nanometric acoustic waves in nanostructures is critically important for the development of miniaturized acoustic devices.In this study,we probe the optically-excited acoustic waves in a single silicon nanowire(NW)using the time-resolved(tr-)high-order Laue-zone(HOLZ)lines under convergent-beam electron diffraction(CBED)conditions in an ultrafast transmission electron microscope(UTEM).We devise an experimental scheme to obtain tr-HOLZ lines under off-zone-axis CBED conditions.We also propose a geometric description of HOLZ line formation and use this alternative description to quantitatively evaluate the dynamics of optically-excited silicon NW.Using part of the deformation gradient tensor,our simulations of the dynamics of Si NW reproduce the experimental results.We further discuss the feasibility of a full retrieval of the deformation gradient tensor by using a set of HOLZ lines from three zone axes.Our findings illustrate a strategy for the quantitative access to dynamical acoustic waves optically excited in micro-and nano-structures using UTEM.

The microscopic crystalline structure of materials is widely recognized as having a profound impact on their functional properties and application potential. Alterations to the lattice often provide distinctive opportunities to finely tune specific properties, particularly in strongly correlated systems. A paradigmatic case is the iron‐based high‐temperature superconductors, where the microstructure plays an important role in modulating superconductivity. In this work, aberration‐corrected scanning transmission electron microscopy (STEM) is employed to investigate the microstructure and intrinsic chemical heterogeneity of Fe 1+y Te, Fe 1+y Te 0.8 Se 0.2 , and Fe 1+y Te 0.5 Se 0.5 . A previously unforeseen superstructure phase, characterized by a wave vector q = (0.4, 0, 0.5), arising from the ordered arrangement of interstitial iron atoms, is clearly visible in the parent compound Fe 1+y Te. Under these specific structural conditions, interstitial iron atoms interact with adjacent Fe atoms, forming iron polycomplexes that induce pronounced distortions in the FeTe 4 tetrahedra and may potentially foster the emergence of ferromagnetic clusters. The experimental findings further illustrate that appropriate Se substitution effectively suppresses interstitial iron concentration and ordering, with Fe 1+y Te 0.5 Se 0.5 notably exhibiting the lowest concentration. The observations also suggest that Se substitution occurs randomly and Te/Se‐induced nanoscale phase separation, driven by chemical heterogeneity is commonly observed within Fe 1+y Te 1−x Se x crystals.

Orbital-selective many-body effects, in which electrons occupying different orbitals experience distinct interaction strengths, play a crucial role in correlated multiorbital materials. However, these effects usually manifest in a complex manner, obscuring their microscopic origins. Here, by combining angle-resolved photoemission spectroscopy measurements with theoretical calculations, we reveal pronounced orbital selectivity in both electron-electron correlation and electron-phonon coupling in the van der Waals material V2Se2O. Electron correlation induces distinct bandwidth renormalization exclusively in the V d_xy-derived band, while the bands mainly composed of the other d orbitals remain essentially unrenormalized. Orbital-resolved analyses identify that the filling number and the bandwidth are decisive factors governing orbital-dependent correlation. Simultaneously, the d_(xz/yz)-derived band exhibits a sharp kink anomaly, arising from enhanced coupling to high-energy phonon modes dominated by oxygen vibrations. Such pronounced orbital selectivity positions V2Se2O as a rare and prototypical platform for unravelling the microscopic mechanisms of orbital-selective electron-electron and electron-phonon interactions, and offers guiding principles for the design of correlated multiorbital materials.