Polar topologies in complex oxides gives rise to a rich spectrum of emergent functionalities and are fundamentally governed by three-dimensional (3D) atomic structures. However, direct experimental determination of buried 3D polar configurations remains a longstanding challenge because conventional (scanning) transmission electron microscopy ((S)TEM) provides primarily projected structural information with limited depth sensitivity. Here, we combine depth-sectioning low-angle annular dark-field (LAADF) STEM, high-angle ADF (HAADF) STEM, and multislice electron ptychography (MEP) to directly visualize the depth-dependent atomic structure and polarization topology in a PTO/STO superlattice. Depth-sectioning STEM reveals pronounced focal-depth-dependent contrast variations and apparent splitting of Pb atomic columns, indicating significant structural heterogeneity along the beam direction. MEP reconstruction simultaneously resolves the Pb, Ti, and O sublattices with nanometer-scale depth resolution, enabling quantitative mapping of atomic displacements throughout the reconstructed volume. The resulting 3D atomic model reveals substantial depth-dependent displacements of Pb, Ti, and O atoms and a corresponding evolution of the polarization topology. Vortex-like polarization structures are observed near the specimen surfaces but become strongly suppressed within the interior, where distinct polarization configurations emerge. These findings show that polarization patterns observed in conventional projection images can arise from the superposition of multiple depth-dependent polar states and may obscure the underlying 3D polarization texture. Our findings establish a direct experimental link between local atomic displacements and depth-dependent polarization topology, opening new opportunities for investigating and engineering buried functional states in complex oxide nanostructures.

High-permittivity (k > 115), crystalline SrTiO3 (STO) thin films were transferred on GaN using a nanomembrane transfer technique for potential applications in high-voltage power devices, including transistors and diodes. The electrical properties of the transferred STO films were systematically characterized using MOS capacitors (MOSCAP), including leakage current characteristics, capacitance-voltage (C-V) behavior, dielectric constant, and frequency dispersion. The STO nanomembranes exhibited negligible leakage current, below the noise floor of the measurement system, up to bias voltages of 6 V and 11 V for the 50 nm and 200 nm thick membranes, respectively. The C-V characteristics indicated high dielectric quality, with minimal frequency dispersion observed over the frequency range of 10 kHz-500 kHz. The extracted dielectric constant (median) ranged from 50 to 110 for the 50 nm STO membrane and from 130 to 190 for the 200 nm STO membrane. Post-transfer thermal annealing in ambient atmosphere at 250 degrees C for two hours resulted in a modest enhancement of the dielectric constant by approximately 8%-20%. However, this improvement was accompanied by degradation in leakage current performance, manifested as a reduction of approximately 1-3 V in the bias range where leakage current was negligible. The underlying physical mechanisms contributing to these trends were analyzed and discussed. In addition, the statistical distribution of the extracted dielectric constant across different pad sizes and nanomembrane thicknesses was reported, and the possible contributors to the apparent trends were discussed.

The anomalous Hall effect and magneto-optical Kerr effect have traditionally been associated with ferromagnets, but recent studies reveal their presence in noncollinear antiferromagnets due to nonzero Berry curvature despite negligible net magnetization. However, Hall measurements often show strong temperature dependence caused by extrinsic scattering, complicating quantitative analysis, and temperature invariance of the Kerr effect remains unconfirmed. Here we employ epitaxial, stoichiometric Mn3NiN single crystal films and perform polar Kerr measurements at an infrared 1550 nm telecommunication wavelength, demonstrating a spontaneous Kerr signal that remains stable within a few percent across a 200 Kelvin range below the Néel temperature. This temperature-invariant Kerr effect contrasts with the strongly temperature-dependent Hall effect and confirms the intrinsic nature of Berry curvature in these materials. Our findings establish infrared Kerr effect as a reliable, local probe of Berry curvature in noncollinear antiferromagnets, facilitating quantitative characterization and advancing antiferromagnetic spintronic applications.

We present a nematic response function model (NRFM) for fit-free direct extraction of the characteristic time of ultrafast electronic thermalization in iron-based superconductors, materials with electronic nematicity. By combining the NRFM for polarization-dependent pump-probe measurements of electronic nematic response with the two-temperature model (TTM) for sub-picosecond quasiparticle relaxation, we quantify the electronic thermalization timescales and their anisotropy. The nematic response function is modeled as the difference in normalized reflectivity signals, revealing a pronounced sub-picosecond extremum in signal evolution that directly yields the characteristic electronic thermalization time. This method demonstrates that the NRFM is consistent with TTM fits of transient optical response, yielding electronic thermalization time constants on the order of 110-230 fs for the FeSe1-xTex and Ba(Fe0.92Co0.08)(2)As-2 thin films. The proposed approach can be applied to any material that exhibits electronic nematicity, providing a powerful tool for direct mapping of the relaxation time in nematic materials, avoiding complex experimental data-fitting procedures.

The LaAlO3/SrTiO3 (LAO/STO) interface hosts a gate-tunable superconducting two-dimensional electron gas (2DEG), which can be programmed to create quantum devices, such as ballistic electron waveguides and quantum dots. To fully exploit this platform for quantum transport, a key requirement is the ability to shuttle single electrons, electron pairs, and other exotic states between spatially separated devices with precision. Surface acoustic waves (SAWs), which travel along the surface of a solid, offer a powerful route to achieve this through their moving electrical potential that captures and transfers electrons. In particular, SAWs in the GHz regime enable fast, controlled transport of individual quantum particles. Although this approach is well-explored in GaAs-based 2DEG, SAW generation in STO remains largely unexplored due to the lack of intrinsic piezoelectricity at room temperature. Here, we investigate room-temperature SAWs in LAO/STO and observe SAW modes up to 2.2 GHz with very low propagation loss of the order 10(-3) dB per wavelength. To directly visualize these modes, we employ atomic acoustic force microscopy, achieving sub-micron resolution imaging of the SAW wave forms, providing insight into the electrostriction-induced SAW generation mechanism. Our measurements indicate a shear horizontal-type mode, which provides the ability to couple to in-plane degrees of freedom for future acoustoelectric and quantum device applications. This work studies the fundamentals of SAW excitation and propagation on STO, a widely used and commercially available substrate, enabling straightforward coupling of SAWs to a broad range of materials that can be grown or transferred onto STO.

Superconductivity in strontium titanate has remained enigmatic for over 50 years. The LaAlO3/SrTiO3 (LAO/STO) heterointerface enables systematic dimensional confinement, from two-dimensional electron gas to quasi-one-dimensional nanostructures, providing unprecedented access to this quantum state. While transport measurements in patterned devices reveal puzzling phenomena, including width-independent critical currents and anomalous pairing, suggesting one-dimensional behavior, direct local probes for the patterned interface and its superconducting response have remained lacking. Here, we use ultra-low temperature non-contact atomic force microscopy with dissipation spectroscopy and Kelvin probe force microscopy to locally probe signatures of superconductivity in patterned LAO/STO devices. Spatially resolved energy dissipation measurements reveal signatures of superconductivity with some features confined to edge channels of order ≈200 nm in width. Dissipation spectra exhibit a characteristic nonlinear bias dependence that provides a local diagnostic of superconductivity consistent with the intermediate carrier density near the superconducting dome, which persists up to the critical field. These results demonstrate the ability of atomic force microscopy to probe superconductivity in patterned LAO/STO structures, potentially addressing fundamental, longstanding questions about quantum confinement and transport anomalies in these correlated nanostructures. Superconductivity at the oxide interface of lanthanum aluminate and strontium titanate can be patterned down to the nanometer scale, but its properties have remained a mystery for many decades. The authors present measurements obtained using atomic force microscopy and energy dissipation, which enable imaging and characterization of the superconducting state at the nanoscale under ultra-low-temperature conditions.

Integrating epitaxial thin films of ferroelectric PbTiO3 and paraelectric SrTiO3 into artificially layered periodic superlattices provides a unique platform for tuning strain, depolarization, and interfacial/surface energies, thereby accessing a rich phase diagram of topological polar structures (skyrmions, vortices, merons, or sinusoidal waves) and superstructures (polar supercrystals). Here we show that the 3D arrangement of polar vortices in a supercrystal suppresses thermal conductivity (k) of PTO/STO superlattices (SLs). The temperature dependence of k reflects the evolution of the polar superstructure, as determined by X-ray diffraction and transmission electron microscopy. The comparison with other SLs suggests that the 3D arrangement is crucial for controlling thermal conductivity beyond the usual interfacial scattering. Moreover, we observed an unexpected reduction in thermal conductivity with increasing superlattice thickness, a phenomenon reminiscent of phonon-wave Anderson localization. Our results show that complex polar superstructures can be useful active elements for modulating heat transport in technologies where control over heat dissipation is critical.

Density waves conventionally describe the periodic modulation of charge or spin, yet the spatial modulation of electronic geometry has remained elusive. Here, we report subtle micrometer-scale spatial modulations of the magneto-optical Kerr signal in the noncollinear antiferromagnet Mn3NiN with compensated spins, consistent with a magnetic-field-induced Berry curvature density wave . These Berry curvature modulations exhibit orientations unpinned from the crystal lattice, forming a nematic state that spontaneously breaks rotational symmetry. We attribute this spatial instability to field-induced spatial variations of the spin texture driven by competing magnetic interactions. This discovery unveils a new class of collective order in spin-compensated magnets mediated by the geometric phase of the wavefunction itself. Its wavelength is controlled by chemical doping and its amplitude by magnetic field, providing concrete tuning knobs for antiferromagnetic and altermagnetic spintronics.

The supercurrent diode effect (SDE), characterized by nonreciprocal critical currents, represents a promising building block for future dissipationless electronics and quantum circuits. Realizing SDE requires breaking both time-reversal and inversion symmetry in the device. Here we use conductive atomic force microscope (c-AFM) lithography to pattern reconfigurable superconducting weak links (WLs) at the LaAlO3/KTaO3 (LAO/KTO) interface. By deliberately engineering the WL geometry at the nanoscale, we realize SDE in these devices in the presence of modest out-of-plane magnetic fields. The SDE polarity can be reversed by simply changing the WL position, and the rectification efficiency reaches up to 13% under optimal magnetic field conditions. Time-dependent Ginzburg-Landau simulations reveal that the observed SDE originates from asymmetric vortex motion in the inversion-symmetry-breaking device geometry. This demonstration of SDE in the LAO/KTO system establishes a versatile platform for investigating and engineering vortex dynamics, forming the basis for engineered quantum circuit elements.

Electrically tunable nonlinear optical responses at the nanoscale remain challenging to achieve because conventional nonlinear materials lack the combination of large susceptibility, nanoscale confinement, and in situ reconfigurability. Here we report electric-field-induced second harmonic (EFISH) generation from a nanoscale tunnel junction defined by conductive atomic force microscope lithography at the LaAlO_3/SrTiO_3 interface. A conducting channel written at the interface is interrupted by a nanoscale insulating gap, across which applied DC bias produces local electric fields exceeding 10^7 V/m. The SHG signal is spatially localized at the junction, exhibits a quadratic bias dependence described by I(2ω) ∝ |χ^(2)_0 + χ^(3) E_DC|^2 with no hysteresis, a modulation depth exceeding 380

The discovery of the intrinsic anomalous Hall effect (AHE) in noncollinear antiferromagnets has opened a plethora of promising opportunities in antiferromagnetic devices. The key challenges limiting their full potential are (i) high-quality epitaxial thin-film growth and (ii) the understanding of Berry curvature and antiferromagnetic domain physics. Here, we focus on a noncollinear antiperovskite antiferromagnet Mn3NiN as a model system, successfully grown as a single-crystal epitaxial thin film. Combining multiple experiments supported by theoretical calculations, we probe the Berry curvature associated with antiferromagnetic Γ4g domains in Mn3NiN and its strong connection to an AHE. We directly image the antiferromagnetic domains driving the intrinsic Berry curvature with high-resolution Sagnac MOKE (magneto-optical Kerr-effect) microscopy, controlling spatial distribution and dynamics by varying temperature and applied magnetic fields. Our findings provide critical advancement of the fundamental understanding and wide tunability of Berry curvature in noncollinear antiferromagnets important for realization in potential spintronic applications.

ABSTRACT The spin cycloid characteristic of noncollinear antiferromagnets offers significant potential for energy‐efficient, magnon‐mediated spintronic applications. Multiferroic BiFeO 3 is among the most promising candidate materials because its antiferromagnetic order can be controlled by an electric field. However, in epitaxial BiFeO 3 thin films, substrate clamping and epitaxial strain modify the cycloidal magnetic structure while limiting efficient ferroelastic‐ferroelectric switching. Here, we show that strain‐released freestanding BiFeO 3 membranes overcome these limitations. Compared with substrate‐clamped epitaxial thin films, a 100‐nm‐thick freestanding membrane exhibits ≈50% faster electric‐field‐driven ferroelectric switching and a spatially uniform, bulk‐like single spin cycloid, as revealed by resonant elastic X‐ray scattering. In contrast, the epitaxial thin film exhibits an expanded cycloid periodicity and slower ferroelectric switching dynamics, reflecting the influence of substrate‐induced strain. Freestanding BiFeO 3 membranes therefore overcome substrate‐induced constraints by simultaneously restoring the intrinsic bulk‐like spin cycloid and enabling substantially faster ferroelectric switching. This combination of robust noncollinear antiferromagnetic order and efficient electric‐field switching establishes freestanding BiFeO 3 membranes as a promising magnetoelectric platform for low‐power magnonic and spintronic technologies, while enabling heterogeneous integration with Si‐based devices.

Freestanding complex oxide membranes enable the release and transfer of epitaxial films, offering new design freedoms for next-generation electronics. While the LaAlO3/SrTiO3 (LAO/STO) heterostructure exhibits remarkable tunable conductivity at its interface, the active interface remains buried beneath the substrate, limiting access to this functionality. Here, we demonstrate how the LAO/STO heterostructure, in membrane form, can be flipped and precisely positioned on silicon and other platforms using polymer-free micromanipulation. The transferred membranes preserve atomically smooth surfaces, high crystallinity, and key electronic properties. Through the 44-nm insulating STO layer, ultra-low-voltage electron-beam lithography (ULV-EBL) writes conductive nanostructures at the now-accessible STO/LAO interface, offering the potential to function as programmable local gates that modulate charge carriers in the underlying silicon. The platform establishes a general strategy for integrating complex oxide heterostructures with semiconductors, quantum materials, and flexible substrates, enabling new architectures for reprogrammable nanoelectronic devices.

The LaAlO_3/SrTiO_3 (LAO/STO) interface hosts a gate-tunable superconducting two-dimensional electron gas (2DEG) which can be programmed to create quantum devices such as ballistic electron waveguides and quantum dots. To fully exploit this platform for quantum transport, a key requirement is the ability to shuttle single electrons, electron pairs, and other exotic states between spatially separated devices with precision. Surface acoustic waves (SAWs), which travel along the surface of a solid, offer a powerful route to achieve this through their moving electrical potential that captures and transfers electrons.

Pump-probe reflectivity reveals coherent acoustic oscillations at 33 and 8.2 GHz in a Ba(Fe_0.92Co_0.08)_2As_2 thin film. The acoustic response was analyzed using a modified logistic-function model, suggesting a temporal redistribution of coherent acoustic energy consistent with anharmonic decay of the higher-frequency mode into the lower-frequency mode.

Superconductivity at oxide interfaces has intrigued researchers for decades, yet the underlying pairing mechanism remains elusive. Here we demonstrate that proximity to a ferroelectric quantum critical point dramatically enhances interfacial superconductivity in KTaO3. By precisely tuning KTaO3 to its quantum critical composition through 0.8

Single-layer FeSe on SrTiO3(001) substrates shows a superconducting transition temperature much higher than that of bulk FeSe, which has been attributed to factors such as electron doping, interfacial electron-phonon coupling, and electron correlations. To pinpoint the primary driver, we grew single-layer FeSe films on SrTiO3(001) substrates with coexisting TiO2 and SrO surface terminations. Scanning tunneling spectroscopy revealed a larger superconducting gap (17.0 meV) on the TiO2-termination than on the SrO-termination (10.5 meV). Tunneling spectroscopy also showed a larger work function on the SrO surface, resulting in reduced charge transfer to FeSe, as confirmed by angle-resolved photoemission spectroscopy. Scanning transmission electron microscopy further revealed distinctive interfacial atomic-scale structures, with the Se-Fe-Se tetrahedral angle changing from 109.5° on the SrO-termination to 104.9° on the TiO2-termination. Compared to dynamical mean field theory calculations, our results indicate that enhanced superconductivity in single-layer FeSe/TiO2 arises from optimal electron correlations, in addition to sufficient charge transfer from the substrate.

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.

Recent breakthroughs in ultrathin, single-crystalline, freestanding complex oxide systems have sparked industry interest in their potential for next-generation commercial devices1,2. However, the mass production of these ultrathin complex oxide membranes has been hindered by the challenging requirement of inserting an artificial release layer between the epilayers and substrates3,4. Here we introduce a technique that achieves atomic precision lift-off of ultrathin membranes without artificial release layers to facilitate the high-throughput production of scalable, ultrathin, freestanding perovskite systems. Leveraging both theoretical insights and empirical evidence, we have identified the pivotal role of lead in weakening the interface. This insight has led to the creation of a universal exfoliation strategy that enables the production of diverse ultrathin perovskite membranes less than 10 nm. Our pyroelectric membranes demonstrate a record-high pyroelectric coefficient of 1.76 × 10-2 C m-2 K-1, attributed to their exceptionally low thickness and freestanding nature. Moreover, this method offers an approach to manufacturing cooling-free detectors that can cover the full far-infrared spectrum, marking a notable advancement in detector technology5.

To achieve efficient anti-damping switching of nanoscale magnetic memories with perpendicular magnetic anisotropy using spin-orbit torque requires that the anti-damping spin-orbit torque have a strong out-of-plane component. The spin anomalous Hall effect and the planar Hall effect spin current produced by a ferromagnetic layer are candidate mechanisms for producing such an out-of-plane anti-damping torque, but both require that the magnetic moment of the spin source layer be canted partly out of the sample plane at zero applied magnetic field. Here we demonstrate such a canted configuration for a ferromagnetic SrRuO3 layer and we characterize all vector components of the torque that it produces, including non-zero out-of-plane anti-damping torques. We verify that the out-of-plane spin component can be tuned by the orientation of magnetic moment, with significant contributions from both the spin anomalous Hall effect and the planar Hall effect spin current.