Unraveling Enhanced Superconductivity in Single-Layer FeSe through Substrate Surface Terminations.

Single-layer FeSe on SrTiO(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 SrTiO(001) substrates with coexisting TiO and SrO surface terminations. Scanning tunneling spectroscopy revealed a larger superconducting gap (17.

Direct Imaging of Co-CUK-1 Framework with HO Guests.

The flexible architectural design of metal clusters and organic ligands attributes Metal-Organic Frameworks (MOFs) as one of the most versatile materials. Host-guest interactions contribute to this versatility, highlighting the need for a fundamental understanding of host frame-guest molecule units. Herein, ab-initio calculations elucidate the spatial distribution of HO guest molecules (guests) within [101] honeycomb channel of Co-CUK-1, where the HO guests are 1D aligned with the highest superposition density.

Sub-unit-cell-segmented ferroelectricity in brownmillerite oxides by phonon decoupling.

The ultimate scaling limit in ferroelectric switching has been attracting broad attention in the fields of materials science and nanoelectronics. Despite immense efforts to scale down ferroelectric features, however, only few materials have been shown to exhibit ferroelectricity at the unit-cell level. Here we report a controllable unit-cell-scale domain in brownmillerite oxides consisting of alternating octahedral/tetrahedral layers.

Oxygen Vacancy Defect Engineering for Transverse Thermoelectric Enhancement: a Novel Extrinsic Pathway beyond Intrinsic Approaches.

For efficient transverse thermoelectric (TE) generation, research has primarily focused on achieving high transverse TE conductivity by utilizing intrinsic material properties. While this approach remains fundamental, exploring extrinsic strategies, such as defect engineering, offers new opportunities to further enhance performance and expand the range of applicable materials. This study investigates the impact of oxygen vacancies-an extrinsic factor-on the anomalous Nernst effect, a key transverse TE mechanism, using disordered semiconducting SrYCoO (δ = 0.

Liquid-like spin dynamics in a hybrid Heisenberg-Ising antiferromagnet.

Two-dimensional (2D) materials and their heterostructures enable unconventional electronic properties and functionalities not accessible in their bulk counterparts. This approach is now being extended to magnetic materials to engineer their spin structures and magnetic fields produced by them. However, spin dynamics of 2D magnetic heterostructures remain largely unexplored.

Protonation-Driven Polarization Retention Failure in Nano-Columnar Lead-Free Ferroelectric Thin Films.

Understanding microscopic mechanisms of polarization retention characteristics in ferroelectric thin films is of great significance for exploring unusual physical phenomena inaccessible in the bulk counterparts and for realizing thin-film-based functional electronic devices. Perovskite (K,Na)NbO is an excellent class of lead-free ferroelectric oxides attracting tremendous interest thanks to its potential applications to nonvolatile memory and eco-friendly energy harvester/storage. Nonetheless, in-depth investigation of ferroelectric properties of (K,Na)NbO films and the following developments of nano-devices are limited due to challenging thin-film fabrication associated with nonstoichiometry by volatile K and Na atoms.

Crystallographic Pathways to Tailoring Metal-Insulator Transition through Oxygen Transport in VO.

The metal-insulator (MI) transition of vanadium dioxide (VO) is effectively modulated by oxygen vacancies, which decrease the transition temperature and insulating resistance. Oxygen vacancies in thin films can be driven by oxygen transport using electrochemical potential. This study delves into the role of crystallographic channels in VO in facilitating oxygen transport and the subsequent tuning of electrical properties.

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.

Spin-Orbit Torque Switching in an All-Van der Waals Heterostructure.

Current-induced control of magnetization in ferromagnets using spin-orbit torque (SOT) has drawn attention as a new mechanism for fast and energy efficient magnetic memory devices. Energy-efficient spintronic devices require a spin-current source with a large SOT efficiency (ξ) and electrical conductivity (σ), and an efficient spin injection across a transparent interface. Herein, single crystals of the van der Waals (vdW) topological semimetal WTe  and vdW ferromagnet Fe GeTe are used to satisfy the requirements in their all-vdW-heterostructure with an atomically sharp interface.

Twisted van der Waals Josephson Junction Based on a High- Superconductor.

Stacking two-dimensional van der Waals (vdW) materials rotated with respect to each other show versatility for studying exotic quantum phenomena. In particular, anisotropic layered materials have great potential for such twistronics applications, providing high tunability. Here, we report anisotropic superconducting order parameters in twisted BiSrCaCuO (Bi-2212) vdW junctions with an atomically clean vdW interface, achieved using the microcleave-and-stack technique.

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.

Template Engineering of Metal-to-Insulator Transitions in Epitaxial Bilayer Nickelate Thin Films.

Understanding metal-to-insulator phase transitions in solids has been a keystone not only for discovering novel physical phenomena in condensed matter physics but also for achieving scientific breakthroughs in materials science. In this work, we demonstrate that the transport properties (i.e.

Heterogeneous integration of single-crystalline rutile nanomembranes with steep phase transition on silicon substrates.

Unrestricted integration of single-crystal oxide films on arbitrary substrates has been of great interest to exploit emerging phenomena from transition metal oxides for practical applications. Here, we demonstrate the release and transfer of a freestanding single-crystalline rutile oxide nanomembranes to serve as an epitaxial template for heterogeneous integration of correlated oxides on dissimilar substrates. By selective oxidation and dissolution of sacrificial VO buffer layers from TiO/VO/TiO by HO, millimeter-size TiO single-crystalline layers are integrated on silicon without any deterioration.

TEM sample preparation using micro-manipulator for in-situ MEMS experiment.

Growing demands for comprehending complicated nano-scale phenomena in atomic resolution has attracted in-situ transmission electron microscopy (TEM) techniques for understanding their dynamics. However, simple to safe TEM sample preparation for in-situ observation has been limited. Here, we suggested the optical microscopy based micro-manipulating system for transferring TEM samples.

Tunable high-temperature itinerant antiferromagnetism in a van der Waals magnet.

Discovery of two dimensional (2D) magnets, showing intrinsic ferromagnetic (FM) or antiferromagnetic (AFM) orders, has accelerated development of novel 2D spintronics, in which all the key components are made of van der Waals (vdW) materials and their heterostructures. High-performing and energy-efficient spin functionalities have been proposed, often relying on current-driven manipulation and detection of the spin states. In this regard, metallic vdW magnets are expected to have several advantages over the widely-studied insulating counterparts, but have not been much explored due to the lack of suitable materials.

Flexopiezoelectricity at ferroelastic domain walls in WO films.

The emergence of a domain wall property that is forbidden by symmetry in bulk can offer unforeseen opportunities for nanoscale low-dimensional functionalities in ferroic materials. Here, we report that the piezoelectric response is greatly enhanced in the ferroelastic domain walls of centrosymmetric tungsten trioxide thin films due to a large strain gradient of 10 m, which exists over a rather wide width (~20 nm) of the wall. The interrelationship between the strain gradient, electric polarity, and the electromechanical property is scrutinized by detecting of the lattice distortion using atomic scale strain analysis, and also by detecting the depolarized electric field using differential phase contrast technique.

Directional ionic transport across the oxide interface enables low-temperature epitaxy of rutile TiO.

Heterogeneous interfaces exhibit the unique phenomena by the redistribution of charged species to equilibrate the chemical potentials. Despite recent studies on the electronic charge accumulation across chemically inert interfaces, the systematic research to investigate massive reconfiguration of charged ions has been limited in heterostructures with chemically reacting interfaces so far. Here, we demonstrate that a chemical potential mismatch controls oxygen ionic transport across TiO/VO interfaces, and that this directional transport unprecedentedly stabilizes high-quality rutile TiO epitaxial films at the lowest temperature (≤ 150 °C) ever reported, at which rutile phase is difficult to be crystallized.

Nearly room temperature ferromagnetism in a magnetic metal-rich van der Waals metal.

In spintronics, two-dimensional van der Waals crystals constitute a most promising material class for long-distance spin transport or effective spin manipulation at room temperature. To realize all-vdW-material-based spintronic devices, however, vdW materials with itinerant ferromagnetism at room temperature are needed for spin current generation and thereby serve as an effective spin source. We report theoretical design and experimental realization of a iron-based vdW material, FeGeTe, showing a nearly room temperature ferromagnetic order, together with a large magnetization and high conductivity.

Improvements in structural and optical properties of wafer-scale hexagonal boron nitride film by post-growth annealing.

Remarkable improvements in both structural and optical properties of wafer-scale hexagonal boron nitride (h-BN) films grown by metal-organic chemical vapor deposition (MOCVD) enabled by high-temperature post-growth annealing is presented. The enhanced crystallinity and homogeneity of the MOCVD-grown h-BN films grown at 1050 °C is attributed to the solid-state atomic rearrangement during the thermal annealing at 1600 °C. In addition, the appearance of the photoluminescence by excitonic transitions as well as enlarged optical band gap were observed for the post-annealed h-BN films as direct consequences of the microstructural improvement.

Configurable topological textures in strain graded ferroelectric nanoplates.

Topological defects in matter behave collectively to form highly non-trivial structures called topological textures that are characterised by conserved quantities such as the winding number. Here we show that an epitaxial ferroelectric square nanoplate of bismuth ferrite subjected to a large strain gradient (as much as 10 m) associated with misfit strain relaxation enables five discrete levels for the ferroelectric topological invariant of the entire system because of its peculiar radial quadrant domain texture and its inherent domain wall chirality. The total winding number of the topological texture can be configured from - 1 to 3 by selective non-local electric switching of the quadrant domains.

Directing Oxygen Vacancy Channels in SrFeO Epitaxial Thin Films.

Transition-metal oxides (TMOs) with brownmillerite (BM) structures possess one-dimensional oxygen vacancy channels (OVCs), which play a key role in realizing high ionic conduction at low temperatures. The controllability of the vacancy channel orientation, thus, possesses a great potential for practical applications and would provide a better visualization of the diffusion pathways of ions in TMOs. In this study, the orientations of the OVCs in BM-SrFeO are stabilized along two crystallographic directions of the epitaxial thin films.

Unleashing the Full Potential of Magnetoelectric Coupling in Film Heterostructures.

A record-high, near-theoretical intrinsic magnetoelectric (ME) coupling of 7 V cm Oe is achieved in a heterostructure of piezoelectric Pb(Zr,Ti)O (PZT) film deposited on magnetostrictive Metglas (FeBSi). The anchor-like, nanostructured interface between PZT and Metglas, improved crystallinity of PZT by laser annealing, and optimum volume of crystalline PZT are found to be the key factors in realizing such a giant strain-mediated ME coupling.

Enhanced polarization by the coherent heterophase interface between polar and non-polar phases.

A piezoelectric composite containing the ferroelectric polar (Bi(Na0.8K0.2)0.