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Since the discovery of high-temperature superconductivity in copper oxide materials 1 , there have been sustained efforts to both understand the origins of this phase and discover new cuprate-like superconducting materials 2 . One prime materials platform has been the rare-earth nickelates and, indeed, superconductivity was recently discovered in the doped compound Nd 0.8 Sr 0.2 NiO 2 (ref. 3 ). Undoped NdNiO 2 belongs to a series of layered square-planar nickelates with chemical formula Nd n +1 Ni n O 2 n +2 and is known as the ‘infinite-layer’ ( n  =  ∞ ) nickelate. Here we report the synthesis of the quintuple-layer ( n  = 5) member of this series, Nd 6 Ni 5 O 12 , in which optimal cuprate-like electron filling ( d 8.8 ) is achieved without chemical doping. We observe a superconducting transition beginning at ~13 K. Electronic structure calculations, in tandem with magnetoresistive and spectroscopic measurements, suggest that Nd 6 Ni 5 O 12 interpolates between cuprate-like and infinite-layer nickelate-like behaviour. In engineering a distinct superconducting nickelate, we identify the square-planar nickelates as a new family of superconductors that can be tuned via both doping and dimensionality. The authors report a superconducting transition beginning at 13 K in films of the quintuple-layer nickelate Nd 6 Ni 5 O 12 .

Collective interactions in functional materials can enable novel macroscopic properties like insulator-to-metal transitions. While implementing such materials into field-effect-transistor technology can potentially augment current state-of-the-art devices by providing unique routes to overcome their conventional limits, attempts to harness the insulator-to-metal transition for high-performance transistors have experienced little success. Here, we demonstrate a pathway for harnessing the abrupt resistivity transformation across the insulator-to-metal transition in vanadium dioxide (VO 2 ), to design a hybrid-phase-transition field-effect transistor that exhibits gate controlled steep (‘sub- kT/q ’) and reversible switching at room temperature. The transistor design, wherein VO 2 is implemented in series with the field-effect transistor’s source rather than into the channel, exploits negative differential resistance induced across the VO 2 to create an internal amplifier that facilitates enhanced performance over a conventional field-effect transistor. Our approach enables low-voltage complementary n-type and p-type transistor operation as demonstrated here, and is applicable to other insulator-to-metal transition materials, offering tantalizing possibilities for energy-efficient logic and memory applications. The intrinsic properties of conventional semiconductors limits the speed and efficiency of field-effect transistors. Here, the authors take advantage of the insulator-to-metal transition in vanadium dioxide to create a transistor with reversible and steep-slope switching at room temperature.

Spontaneous polarization and crystallographic orientations within ferroelectric domains are investigated using an epitaxially grown BiFeO 3 thin film under bi-axial tensile strain. Four dimensional-scanning transmission electron microscopy (4D-STEM) and atomic resolution STEM techniques revealed that the tensile strain applied is not enough to cause breakdown of equilibrium BiFeO 3 symmetry (rhombohedral with space group: R3c ). 4D-STEM data exhibit two types of BiFeO 3 ferroelectric domains: one with projected polarization vector possessing out-of-plane component only, and the other with that consisting of both in-plane and out-of-plane components. For domains with only out-of-plane polarization, convergent beam electron diffraction (CBED) patterns exhibit “extra” Bragg’s reflections (compared to CBED of cubic-perovskite) that indicate rhombohedral symmetry. In addition, beam damage effects on ferroelectric property measurements were investigated by systematically changing electron energy from 60 to 300 keV.

A BiFeO 3 film is grown epitaxially on a PrScO 3 single crystal substrate which imparts ~ 1.45% of biaxial tensile strain to BiFeO 3 resulting from lattice misfit. The biaxial tensile strain effect on BiFeO 3 is investigated in terms of crystal structure, Poisson ratio, and ferroelectric domain structure. Lattice resolution scanning transmission electron microscopy, precession electron diffraction, and X-ray diffraction results clearly show that in-plane interplanar distance of BiFeO 3 is the same as that of PrScO 3 with no sign of misfit dislocations, indicating that the biaxial tensile strain caused by lattice mismatch between BiFeO 3 and PrScO 3 are stored as elastic energy within BiFeO 3 film. Nano-beam electron diffraction patterns compared with structure factor calculation found that the BiFeO 3 maintains rhombohedral symmetry, i.e., space group of R3c . The pattern analysis also revealed two crystallographically distinguishable domains. Their relations with ferroelectric domain structures in terms of size and spontaneous polarization orientations within the domains are further understood using four-dimensional scanning transmission electron microscopy technique.

The layered square-planar nickelates, Nd n +1 Ni n O 2 n +2 , are an appealing system to tune the electronic properties of square-planar nickelates via dimensionality; indeed, superconductivity was recently observed in Nd 6 Ni 5 O 12 thin films. Here, we investigate the role of epitaxial strain in the competing requirements for the synthesis of the n  = 3 Ruddlesden-Popper compound, Nd 4 Ni 3 O 10 , and subsequent reduction to the square-planar phase, Nd 4 Ni 3 O 8 . We synthesize our highest quality Nd 4 Ni 3 O 10 films under compressive strain on LaAlO 3 (001), while Nd 4 Ni 3 O 10 on NdGaO 3 (110) exhibits tensile strain-induced rock salt faults but retains bulk-like transport properties. A high density of extended defects forms in Nd 4 Ni 3 O 10 on SrTiO 3 (001). Films reduced on LaAlO 3 become insulating and form compressive strain-induced c -axis canting defects, while Nd 4 Ni 3 O 8 films on NdGaO 3 are metallic. This work provides a pathway to the synthesis of Nd n +1 Ni n O 2 n +2 thin films and sets limits on the ability to strain engineer these compounds via epitaxy. The discovery of superconductivity in the infinite-layer nickelates reignites an interest in the nickelates as cuprate analogues. Here, the authors investigate the role of epitaxial strain in the synthesis of the n=3 layered nickelate, Nd 4 Ni 3 O 8 .

In the Acknowledgements section of this article the grant number relating to NSF was incorrectly given as DMR 2045826 and should have been DMR-2045826. The original article has been corrected.

The prospect of 2‐dimensional electron gases (2DEGs) possessing high mobility at room temperature in wide‐bandgap perovskite stannates is enticing for oxide electronics, particularly to realize transparent and high‐electron mobility transistors. Nonetheless only a small number of studies to date report 2DEGs in BaSnO3‐based heterostructures. Here, 2DEG formation at the LaScO3/BaSnO3 (LSO/BSO) interface with a room‐temperature mobility of 60 cm2 V−1 s−1 at a carrier concentration of 1.7 × 1013 cm–2 is reported. This is an order of magnitude higher mobility at room temperature than achieved in SrTiO3‐based 2DEGs. This is achieved by combining a thick BSO buffer layer with an ex situ high‐temperature treatment, which not only reduces the dislocation density but also produces a SnO2‐terminated atomically flat surface, followed by the growth of an overlying BSO/LSO interface. Using weak beam dark‐field transmission electron microscopy imaging and in‐line electron holography technique, a reduction of the threading dislocation density is revealed, and direct evidence for the spatial confinement of a 2DEG at the BSO/LSO interface is provided. This work opens a new pathway to explore the exciting physics of stannate‐based 2DEGs at application‐relevant temperatures for oxide nanoelectronics. The promise of BaSnO3 (BSO) band structure and scattering channels to relieve low room temperature mobility challenges of interfacial oxide two‐dimensional electron gases has been blocked by structural and point defects. The authors overcome this with a new synthesis approach combining a BSO atomically flat pseudo‐substrate layer with a band‐aligned BSO/LaScO3 oxide interface.

Ultrawide-band-gap (UWBG) oxide semiconductors are emerging as key platforms for next-generation energy-efficient, high-power, and high-frequency electronics. Further performance gains require the discovery of alternative UWBG systems with band gaps well above 4 eV, while offering intrinsically higher carrier mobility and controllable dopability. This paper highlights recent computational predictions and experimental advances toward such materials, with a focus on dopant activation, carrier density control, and phonon-limited mobility. Although computational screening has uncovered numerous promising candidates, most have yet to be realized as high-quality, single-crystalline thin films suitable for scalable devicefabrication. While epitaxial growth offers a unique platform to probe the intrinsic properties of these materials, the experimental realization is often limited by kinetic and processing constraints, such as nucleation dynamics and precise control of growth parameters. This gap often leads to significant deviations from the theoretical ground-state electrical transport properties. We examine the origins of these discrepancies and highlight integrated approaches, combining high-throughput computation with advanced epitaxial synthesis, to accelerate the development of next-generation UWBG oxide semiconductors. Graphical abstract

Epitaxial ultra-thin oxide films can support large percent level strains well beyond their bulk counterparts, thereby enabling strain-engineering in oxides that can tailor various phenomena. At these reduced dimensions (typically < 10 nm), contributions from the substrate can dwarf the signal from the epilayer, making it difficult to distinguish the properties of the epilayer from the bulk. This is especially true for oxide on oxide systems. Here, we have employed a combination of hard X-ray photoelectron spectroscopy (HAXPES) and angular soft X-ray absorption spectroscopy (XAS) to study epitaxial VO2/TiO2 (100) films ranging from 7.5 to 1 nm. We observe a low-temperature (300 K) insulating phase with evidence of vanadium-vanadium (V-V) dimers and a high-temperature (400 K) metallic phase absent of V-V dimers irrespective of film thickness. Our results confirm that the metal insulator transition can exist at atomic dimensions and that biaxial strain can still be used to control the temperature of its transition when the interfaces are atomically sharp. More generally, our case study highlights the benefits of using non-destructive XAS and HAXPES to extract out information regarding the interfacial quality of the epilayers and spectroscopic signatures associated with exotic phenomena at these dimensions.

Spontaneous polarization and crystallographic orientations within ferroelectric domains are investigated using an epitaxially grown BiFeO thin film under bi-axial tensile strain. Four dimensional-scanning transmission electron microscopy (4D-STEM) and atomic resolution STEM techniques revealed that the tensile strain applied is not enough to cause breakdown of equilibrium BiFeO symmetry (rhombohedral with space group: R3c). 4D-STEM data exhibit two types of BiFeO ferroelectric domains: one with projected polarization vector possessing out-of-plane component only, and the other with that consisting of both in-plane and out-of-plane components. For domains with only out-of-plane polarization, convergent beam electron diffraction (CBED) patterns exhibit \"extra\" Bragg's reflections (compared to CBED of cubic-perovskite) that indicate rhombohedral symmetry. In addition, beam damage effects on ferroelectric property measurements were investigated by systematically changing electron energy from 60 to 300 keV.