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Ferroelectric materials are fascinating for their non-volatile switchable electric polarizations induced by the spontaneous inversion-symmetry breaking. However, in all of the conventional ferroelectric compounds, at least two constituent ions are required to support the polarization switching 1 , 2 . Here, we report the observation of a single-element ferroelectric state in a black phosphorus-like bismuth layer 3 , in which the ordered charge transfer and the regular atom distortion between sublattices happen simultaneously. Instead of a homogenous orbital configuration that ordinarily occurs in elementary substances, we found the Bi atoms in a black phosphorous-like Bi monolayer maintain a weak and anisotropic s p orbital hybridization, giving rise to the inversion-symmetry-broken buckled structure accompanied with charge redistribution in the unit cell. As a result, the in-plane electric polarization emerges in the Bi monolayer. Using the in-plane electric field produced by scanning probe microscopy, ferroelectric switching is further visualized experimentally. Owing to the conjugative locking between the charge transfer and atom displacement, we also observe the anomalous electric potential profile at the 180° tail-to-tail domain wall induced by competition between the electronic structure and electric polarization. This emergent single-element ferroelectricity broadens the mechanism of ferroelectrics and may enrich the applications of ferroelectronics in the future. A single-element ferroelectric state is observed in a black phosphorus-like bismuth layer, in which the ordered charge transfer and the regular atom distortion between sublattices happen simultaneously and ferroelectric switching is further visualized experimentally.

In the quest for post-CMOS (complementary metal–oxide–semiconductor) technologies, driven by the need for improved efficiency and performance, topologically protected ferromagnetic ‘whirls’ such as skyrmions 1 – 8 and their anti-particles have shown great promise as solitonic information carriers in racetrack memory-in-logic or neuromorphic devices 1 , 9 – 11 . However, the presence of dipolar fields in ferromagnets, which restricts the formation of ultrasmall topological textures 3 , 6 , 8 , 9 , 12 , and the deleterious skyrmion Hall effect, when skyrmions are driven by spin torques 9 , 10 , 12 , have thus far inhibited their practical implementation. Antiferromagnetic analogues, which are predicted to demonstrate relativistic dynamics, fast deflection-free motion and size scaling, have recently become the subject of intense focus 9 , 13 – 19 , but they have yet to be experimentally demonstrated in natural antiferromagnetic systems. Here we realize a family of topological antiferromagnetic spin textures in α-Fe 2 O 3 —an Earth-abundant oxide insulator—capped with a platinum overlayer. By exploiting a first-order analogue of the Kibble–Zurek mechanism 20 , 21 , we stabilize exotic merons and antimerons (half-skyrmions) 8 and their pairs (bimerons) 16 , 22 , which can be erased by magnetic fields and regenerated by temperature cycling. These structures have characteristic sizes of the order of 100 nanometres and can be chemically controlled via precise tuning of the exchange and anisotropy, with pathways through which further scaling may be achieved. Driven by current-based spin torques from the heavy-metal overlayer, some of these antiferromagnetic textures could emerge as prime candidates for low-energy antiferromagnetic spintronics at room temperature 1 , 9 – 11 , 23 . A family of topological antiferromagnetic spin textures is realized at room temperature in α-Fe 2 O 3 , and their reversible and field-free stabilization using a Kibble–Zurek-like temperature cycling is demonstrated.

Profuse dendritic-synaptic interconnections among neurons in the neocortex embed intricate logic structures enabling sophisticated decision-making that vastly outperforms any artificial electronic analogues 1 – 3 . The physical complexity is far beyond existing circuit fabrication technologies: moreover, the network in a brain is dynamically reconfigurable, which provides flexibility and adaptability to changing environments 4 – 6 . In contrast, state-of-the-art semiconductor logic circuits are based on threshold switches that are hard-wired to perform predefined logic functions. To advance the performance of logic circuits, we are re-imagining fundamental electronic circuit elements by expressing complex logic in nanometre-scale material properties. Here we use voltage-driven conditional logic interconnectivity among five distinct molecular redox states of a metal–organic complex to embed a ‘thicket’ of decision trees (composed of multiple if-then-else conditional statements) having 71 nodes within a single memristor. The resultant current–voltage characteristic of this molecular memristor (a 'memory resistor', a globally passive resistive-switch circuit element that axiomatically complements the set of capacitor, inductor and resistor) exhibits eight recurrent and history-dependent non-volatile switching transitions between two conductance levels in a single sweep cycle. The identity of each molecular redox state was determined with in situ Raman spectroscopy and confirmed by quantum chemical calculations, revealing the electron transport mechanism. Using simple circuits of only these elements, we experimentally demonstrate dynamically reconfigurable, commutative and non-commutative stateful logic in multivariable decision trees that execute in a single time step and can, for example, be applied as local intelligence in edge computing 7 – 9 . Multiple redox transitions in a molecular memristor can be harnessed as ‘decision trees’ to undertake complex and reconfigurable logic operations in a single time step.

Nickel-based complex oxides have served as a playground for decades in the quest for a copper-oxide analog of the high-temperature superconductivity. They may provide clues towards understanding the mechanism and an alternative route for high-temperature superconductors. The recent discovery of superconductivity in the infinite-layer nickelate thin films has fulfilled this pursuit. However, material synthesis remains challenging, direct demonstration of perfect diamagnetism is still missing, and understanding of the role of the interface and bulk to the superconducting properties is still lacking. Here, we show high-quality Nd 0.8 Sr 0.2 NiO 2 thin films with different thicknesses and demonstrate the interface and strain effects on the electrical, magnetic and optical properties. Perfect diamagnetism is achieved, confirming the occurrence of superconductivity in the films. Unlike the thick films in which the normal-state Hall-coefficient changes signs as the temperature decreases, the Hall-coefficient of films thinner than 5.5 nm remains negative, suggesting a thickness-driven band structure modification. Moreover, X-ray absorption spectroscopy reveals the Ni-O hybridization nature in doped infinite-layer nickelates, and the hybridization is enhanced as the thickness decreases. Consistent with band structure calculations on the nickelate/SrTiO 3 heterostructure, the interface and strain effect induce a dominating electron-like band in the ultrathin film, thus causing the sign-change of the Hall-coefficient. Nickelate superconductors attract enormous attention in the field of high-temperature superconductivity. Here the authors report observation of perfect diamagnetism and interfacial effect on the electronic structures in infinite layer Nd 0.8 Sr 0.2 NiO 2 superconductors.

The supermoiré lattice, built by stacking two moiré patterns, provides a platform for creating flat mini-bands and studying electron correlations. An ultimate challenge in assembling a graphene supermoiré lattice is in the deterministic control of its rotational alignment, which is made highly aleatory due to the random nature of the edge chirality and crystal symmetry. Employing the so-called “golden rule of three”, here we present an experimental strategy to overcome this challenge and realize the controlled alignment of double-aligned hBN/graphene/hBN supermoiré lattice, where the twist angles between graphene and top/bottom hBN are both close to zero. Remarkably, we find that the crystallographic edge of neighboring graphite can be used to better guide the stacking alignment, as demonstrated by the controlled production of 20 moiré samples with an accuracy better than ~ 0.2°. Finally, we extend our technique to low-angle twisted bilayer graphene and ABC-stacked trilayer graphene, providing a strategy for flat-band engineering in these moiré materials. The reliable fabrication of 2D heterostructures with controllable moiré patterns is important for the investigation of their emergent physical properties. Here, the authors report an alignment technique enabling the fabrication of double-aligned hBN/graphene/hBN supermoiré lattice structures with a yield close to 100%.

Antiferromagnetic insulators are a ubiquitous class of magnetic materials, holding the promise of low-dissipation spin-based computing devices that can display ultra-fast switching and are robust against stray fields. However, their imperviousness to magnetic fields also makes them difficult to control in a reversible and scalable manner. Here we demonstrate a novel proof-of-principle ionic approach to control the spin reorientation (Morin) transition reversibly in the common antiferromagnetic insulator α-Fe 2 O 3 (haematite) – now an emerging spintronic material that hosts topological antiferromagnetic spin-textures and long magnon-diffusion lengths. We use a low-temperature catalytic-spillover process involving the post-growth incorporation or removal of hydrogen from α-Fe 2 O 3 thin films. Hydrogenation drives pronounced changes in its magnetic anisotropy, Néel vector orientation and canted magnetism via electron injection and local distortions. We explain these effects with a detailed magnetic anisotropy model and first-principles calculations. Tailoring our work for future applications, we demonstrate reversible control of the room-temperature spin-state by doping/expelling hydrogen in Rh-substituted α-Fe 2 O 3 . One major challenge for antiferromagnetic spintronics is how to control the antiferromagnetic state. Here Jani et al. demonstrate the reversible ionic control of the room-temperature magnetic anisotropy and spin reorientation transition in haematite, via the incorporation and removal of hydrogen.

A key open question in the study of layered superconducting nickelate films is the role that hydrogen incorporation into the lattice plays in the appearance of the superconducting state. Due to the challenges of stabilizing highly crystalline square planar nickelate films, films are prepared by the deposition of a more stable parent compound which is then transformed into the target phase via a topotactic reaction with a strongly reducing agent such as CaH 2 . Recent studies, both experimental and theoretical, have introduced the possibility that the incorporation of hydrogen from the reducing agent into the nickelate lattice may be critical for the superconductivity. In this work, we use secondary ion mass spectrometry to examine superconducting La 1− x X x NiO 2 / SrTiO 3 ( X = Ca and Sr) and Nd 6 Ni 5 O 12 / NdGaO 3 films, along with non-superconducting NdNiO 2 / SrTiO 3 and (Nd,Sr)NiO 2 / SrTiO 3 . We find no evidence for extensive hydrogen incorporation across a broad range of samples, including both superconducting and non-superconducting films. Theoretical calculations indicate that hydrogen incorporation is broadly energetically unfavorable in these systems, supporting our conclusion that extensive hydrogen incorporation is not generally required to achieve a superconducting state in layered square-planar nickelates. The role of hydrogen in engendering superconductivity in layered nickelates is under intense debate. Here, the authors perform secondary ion mass spectroscopy and see no evidence for extensive hydrogen incorporation into superconducting nickelates.

Soft ferromagnetic permalloy (NiFe) thin films are promising for applications in spintronic devices because of their constituent electrical and magnetic properties. Electron beam evaporation and sputtering techniques have been used to deposit NiFe thin films. For in situ stacking of NiFe with functional complex oxides, the pulsed laser deposition (PLD) method is highly desirable. However, the growth of high‐quality NiFe (and non‐oxide thin films in general) by PLD remains a formidable task. Here, high‐quality NiFe thin films of various thicknesses on oxide/non‐oxide substrates with desirable magnetic properties by PLD at room temperature are reported. The magnetic properties are found to be strongly dependent on the laser fluence of the deposition process. The laser fluence of 4 J cm−2 produces the highest magnetization of ≈547 emu cc−1. The small coercivity (few Oersted) and sharp ferromagnetic switching behavior indicate uniaxial anisotropy with an easy axis along the in‐plane direction. In addition, thickness‐dependent magnetodynamics characterizations are studied via ferromagnetic resonance. These results offer significant insight into the PLD‐based development of thin metal magnetic films. High‐quality NiFe thin films with desirable magnetic properties are deposited on oxide and non‐oxide substrates using pulsed laser deposition (PLD) at room temperature. The structure, magnetic properties, and magnetodynamics characterizations are studied, with their dependence on laser fluence, substrate and thickness analyzed. These findings offer significant insights into the development of thin NiFe films through PLD.

Antiferromagnets hosting real-space topological textures are promising platforms to model fundamental ultrafast phenomena and explore spintronics. However, they have only been epitaxially fabricated on specific symmetry-matched substrates, thereby preserving their intrinsic magneto-crystalline order. This curtails their integration with dissimilar supports, restricting the scope of fundamental and applied investigations. Here we circumvent this limitation by designing detachable crystalline antiferromagnetic nanomembranes of α-Fe 2 O 3 . First, we show—via transmission-based antiferromagnetic vector mapping—that flat nanomembranes host a spin-reorientation transition and rich topological phenomenology. Second, we exploit their extreme flexibility to demonstrate the reconfiguration of antiferromagnetic states across three-dimensional membrane folds resulting from flexure-induced strains. Finally, we combine these developments using a controlled manipulator to realize the strain-driven non-thermal generation of topological textures at room temperature. The integration of such free-standing antiferromagnetic layers with flat/curved nanostructures could enable spin texture designs via magnetoelastic/geometric effects in the quasi-static and dynamical regimes, opening new explorations into curvilinear antiferromagnetism and unconventional computing. Topological antiferromagnetic states are generated and spatially reconfigured in free-standing crystalline membranes of haematite through strain design.

Unconventional high‐temperature superconductivity has long been a captivating puzzle in condensed matter physics. The 1987 Nobel Prize in Physics celebrated the discovery of high‐temperature superconductivity in copper oxide ceramics. Nearly four decades later, a broad class of high‐temperature superconducting oxides has yet to be demonstrated, and the fundamental understanding of the pairing mechanism remains inconclusive. Recently, nickel oxides have emerged as a new class of high‐temperature superconductors, beyond copper, where correlated phases can be controlled by doping, pressure, strain, and dimensionality. In this article, we provide our perspective on the recent developments and prospects of the nickel age of high‐temperature superconductivity. The 1987's Nobel Prize in Physics celebrated the discovery of high‐temperature unconventional superconductivity in a ceramic – copper oxide Ba‐La‐Cu‐O with the onset of superconductivity in the 30 K range at ambient pressure. Non‐copper‐based oxides, however, have yet to demonstrate similar high‐temperature superconductivity Tc > 30 K. Recently, breakthroughs in nickel oxides reignited the passion to achieve and study the high‐Tc superconductivity in ceramics.