Wu Zhou

Fe(Te,Se) is a prototypical iron-based superconductor and a promising platform for exploring topological superconductivity. However, growing high-quality ultrathin Fe(Te,Se) films on magnetic substrates remains challenging. Here, we demonstrate epitaxial growth of monolayer-to-trilayer Fe(Te,Se) on the van der Waals itinerant ferromagnet Fe3GeTe2 (FGT) via direct selenization of the substrate, without external Fe or Te deposition. Combined scanning tunneling microscopy/spectroscopy (STM/STS), low-energy electron diffraction (LEED), scanning transmission electron microscopy (STEM), and energy-dispersive spectroscopy (EDS) characterizations reveal large-area, atomically flat tetragonal films with well-defined rotational alignment to the hexagonal FGT lattice. Cross-sectional STEM-EDS confirms Se incorporation and interfacial elemental redistribution. Thickness-dependent spectroscopy reveals evolving electronic structures and progressive decoupling from the ferromagnetic substrate. Measurements across lateral monolayer–bilayer interfaces further uncover asymmetric band bending and charge redistribution driven by Fermi-level equilibration. These findings establish substrate-mediated selenization as a versatile route to ultrathin superconducting heterostructures and magnetic quantum platforms.

The growing demands of artificial intelligence hardware have exposed a fundamental latency bottleneck in conventional floating-gate memory arrays. Although two-dimensional (2D) floating-gate memories have achievd nanosecond-level operations, their large-scale integration remains hindered by the scalability issues of the commonly used hBN dielectric layer. Here, we demonstrate scalable ultrafast non-volatile floating-gate memory arrays with hybrid Y2O3/HfO2 dielectrics as the tunneling layer, achieving ~60 ns ultrafast programming/erasing speeds, high extinction ratios up to ~10⁹, long-term data retention approaching 105 s, and robust cycling endurance exceeding 1800 cycles with multi-bit storage capabilities. A 5 × 5 memory array shows outstanding uniformity in memory window sizes, on/off ratios, and programmed/erased threshold voltages. Furthermore, the floating‑gate memory devices also demonstrate efficient optical erasure with 1,441 A/W responsivity and 9×10¹⁶ Jones detectivity. The promising uniformity of these memory arrays highlights the potential for larger-scale integration and its scalability for high-density storage and photodetection applications.

The origin of superconductivity in oxide interfaces and its relation to ferroelectricity remains an open question. At LaAlO₃/SrTiO₃ interfaces, quantum confinement and inversion symmetry breaking create a two-dimensional electron gas near a ferroelectric quantum critical point, yet direct evidence linking phonon dynamics to electron pairing has been lacking. Here we directly probe lattice vibrations and atomic structure at LaAlO₃/SrTiO₃ interfaces across the superconducting phase diagram using vibrational spectroscopy with momentum selectivity in a scanning transmission electron microscope. We find that superconductivity across the doping series correlates with inversion symmetry breaking and the appearance of high-frequency localized phonons. These tunable, polar vibrations-confined near the interface-exhibit strong electron-phonon coupling and evolve systematically with carrier density. Our findings establish a link between lattice instability, superconductivity and strong electron-phonon coupling mediated by tunable localized phonons, providing new insights into possible microscopic pairing pathways in quantum paraelectric systems.

The physical properties of transition metal oxides are highly sensitive to the concentration and spatial arrangement of oxygen vacancies, which give rise to a rich spectrum of emergent functionalities. Sr _1‐x Y _x CoO _3‐???? represents a complex cobaltite system exhibiting tunable oxygen vacancy configurations and magnetic ordering. Here, we report the observation of an anomalously large magnetic coercive field in epitaxial Sr _1‐x Y _x CoO _3‐???? thin films grown on (001) ((LaAlO ₃ ) _0.3 (Sr ₂ TaAlO ₆ ) _0.7 ) (LSAT) substrates, exceeding 5 T at 30 K with an estimated value of 11.4 T at 2 K. This giant coercivity originates from a long‐range, 2D oxygen vacancy ordered structure that stabilizes a ferromagnetic spin bag mechanism, in which low‐spin Co ³⁺ ions interact cooperatively with neighboring intermediate‐spin Co ³⁺ and high‐spin Co ²⁺ species, forming robust local magnetic domains. Our work establishes a pathway for engineering oxygen vacancy architectures in transition‐metal oxides and demonstrates a strategy for designing atomically tailored quantum materials with highly tunable magnetic and electronic functionalities.

Crystalline phases of transition-metal dichalcogenides offer unique structural configurations and tunable properties, driving phase engineering toward advanced fundamental and applied research. While strain is a recognized driver for modulating phase evolution, achieving spatially precise control over phase transitions remains a significant challenge. In this work, we present a lithography-compatible technique to modulate the phase evolution of TaS₂ flakes by using patterned Al₂O₃ nanofilm stressors. By employing standard photolithography and lift-off processes, exfoliated 1T-TaS₂ flakes were integrated with controllable patterned Al₂O₃ overlayers. Through a combination of on-chip comparative Raman spectroscopy and cross-sectional scanning transmission electron microscopy, we demonstrate that the strain induced by the Al₂O₃ stressor is the governing factor in modulating TaS₂ phase evolution with a thickness-dependent mechanical response. Our work provides a facile and scalable platform for spatially precise strain engineering to modulate phase transitions in transition-metal dichalcogenides toward the fabrication of phase-engineered structures in future nanoelectronic studies.

X-ray linear dichroism has been pivotal for probing electronic anisotropies, but its inherent limited spatial resolution precludes the atomic-scale investigations of orbital polarization. Here we introduce a versatile electron linear dichroism methodology in scanning transmission electron microscopy that overcomes these constraints. Using electron energy loss spectroscopy with an atomic-sized probe and selecting momentum transfers along two orthogonal directions, we directly visualize orbital occupation at individual atomic columns in real space. Using strained La_0.7Sr_0.3MnO₃ thin films as a model system, we resolve the Mn3d e_g orbital polarization with sub-ångström precision. We show that compressive strain stabilizes 3z²-r² occupation whereas tensile strain favours x²-y². These results validate our approach against established X-ray measurements, achieving the ultimate single-atomic-column sensitivity. We further demonstrate two optimized signal extraction protocols that adapt to experimental constraints without compromising sensitivity. This generalizable platform opens unique opportunities to study symmetry-breaking phenomena at individual defects, interfaces and in quantum materials where atomic-scale electronic anisotropy governs emergent functionality.

Entropy engineering has emerged as a promising paradigm for tailoring the electronic and photoelectric properties of materials. Although high-entropy transition metal sulfides have been achieved, entropy engineering in 2D tellurides remains challenging. In this work, we report the successful synthesis of a 1T' monolayer heptanary medium-entropy (ME) alloy (Mo_aW_bFe_cCo_dS_xSe_yTe_z) via a one-step chemical vapor deposition method. Advanced characterizations, including scanning transmission electron microscopy, energy dispersive X-ray spectroscopy and electron energy loss spectroscopy confirm the uniform atomic-level distribution of the seven constituent elements within the alloy. The 1T' ME alloy device exhibits a high drain current of ~ 6.5 mA, which is 216 times higher than the ~ 30 μA observed in pristine 1T' MoTe₂. Furthermore, the 1T' ME alloy photodetector exhibits responsivities of 27.92 A/W at 1064 nm and 63.74 A/W at 1550 nm, outperforming those of the pristine 1T' MoTe₂ by more than two orders of magnitude. This remarkable enhancement is attributed to the reduced Schottky barrier (15.9 meV) at the 1T' ME alloy/electrode interface, along with the enhanced conductance (0.43 S) and reduced thermal activation energy (4.1 meV) in the 1T' ME alloy, collectively facilitating more efficient carrier injection and transport. Our work provides a distinct pathway for tailoring the properties of transition metal dichalcogenides through entropy engineering and offers valuable insights for the design of high-performance infrared photodetectors.

Determining local atomic coordination with element specificity is central to linking structure and functionality in materials, yet quantitative coordination metrics (coordination number, bond length, and disorder) are typically obtained only from ensemble-averaged techniques such as extended X-ray absorption fine structure (EXAFS). This averaging obscures the resolving of structural heterogeneity at interfaces, defects, and dopant sites 1,2. Here we show that extended energy-loss fine structure (EXELFS) in an electron microscope, physically analogous to EXAFS but driven by an electron beam, can deliver quantitative coordination analysis with atomic resolution and single-atom sensitivity. By combining low-voltage scanning transmission electron microscopy (STEM) with dose-fractionated acquisition and direct electron detection, we achieve quantitative coordination analysis at the atomic scale for the first time. We resolve atomic-layer-by-atomic-layer coordination and bond-length disorder across the epitaxial graphene/SiC interface, and distinguish the coordination of individual Si impurities in graphene lattice. These results establish STEM-EXELFS as an atomic-scale coordination probe, enabling direct measurements of local order in complex materials beyond ensemble averaging.