Tetsuya Nakamura

Two-dimensional transition-metal dichalcogenides provide an ideal platform for exploring emergent electronic and magnetic phenomena inaccessible in bulk materials. Here, we realize a metastable monolayer CrS2 film on bilayer graphene/SiC(0001) by combining molecular-beam epitaxy with a topotactic chemical reaction. Angle-resolved photoemission spectroscopy (ARPES), together with first-principles calculations, supports the assignment of monolayer CrS2 to the octahedral 1T structure. ARPES reveals a gap-like semiconducting state that is not reproduced by the GGA+U calculations. X-ray magnetic circular dichroism detects no ferromagnetic response in monolayer 1T-CrS2 down to 160 K, consistent with paramagnetic or antiferromagnetic behavior, in stark contrast to its isostructural counterpart, monolayer CrTe2, which exhibits metallic ferromagnetic behavior. These results establish metastably stabilized monolayer CrS2 as a distinct member of Cr-based two-dimensional materials and provide a foundation for exploring ultrathin semiconductor devices.

We report on the coherence evaluation of the beamline BL09W at NanoTerasu (Tohoku University, Japan) and demonstrate X-ray multi-contrast imaging using an X-ray Talbot interferometer. Fringe visibility was measured in both the horizontal and vertical directions and analyzed to estimate the effective source size of the X-ray beam. The estimated source size in the horizontal direction was consistent with the design specification, confirming the validity of the measurements. In the vertical direction, the high visibility, exceeding 70%, indicates the remarkably high spatial coherence of the source. Multi-contrast computed tomography was successfully performed, simultaneously reconstructing absorption, phase and small-angle scattering contrasts. These results establish BL09W as a versatile beamline for coherence-based X-ray imaging.

Since the fiscal year 2022, `Support Program for Life Science and Drug Discovery Research (BINDS Phase II)', funded by the Japan Agency for Medical Research and Development (AMED), has been supporting structural analysis research in Japan, promoting the further development of various advanced structural analysis technologies. The BINDS project aims to offer more timely and cutting-edge support by establishing a new macromolecular crystallography endstation (MX-ES) at NanoTerasu, Japan's first fourth-generation synchrotron-radiation facility. MX-ES has been equipped with microbeam focusing optics and a state-of-the-art measurement system for fully automated, high-throughput data collection from cooled crystals. Commissioning and initial experiments have been completed. User operations are expected to begin in the second half of the fiscal year 2025.

This paper presents a carbon-based organic field-effect transistor (OFET) developed using screen printing. Carbon materials are electrically conductive, chemically stable, and durable in outdoor settings, rendering carbon-based OFETs highly promising for environmental, Internet of Things, and biosensing applications. However, their temperature-dependent characteristics remain unexplored. We demonstrated carbon-based OFETs operating at 3 V and evaluated their electrical performance across a temperature range relevant to practical environments. By incorporating the observed temperature characteristics into a device simulation model, we achieved excellent reproducibility in circuit simulations. This study advances the understanding and future development of environmentally friendly, printed electronic devices.

NanoTerasu is a new 3 GeV synchrotron radiation facility in Sendai, Japan, which began user operation in April 2024. A station for small-angle X-ray scattering (SAXS) and wide-angle X-ray diffraction (WAXD) has been built at the wiggler beamline BL08W. The station was built in a branch for which an X-ray beam is provided by Bragg reflection from two Si crystals. The X-ray energy is 8.0 or 13.1 keV using either an Si(111) or an Si(220) crystal, respectively. The beam is focused with an Ru-coated bent cylindrical mirror. In the SAXS station, an Anton Paar SAXSpoint 5.0 laboratory X-ray apparatus has been installed. The original X-ray generator and focusing mirror in the laboratory equipment were removed and four-quadrant slits and an ion chamber have been installed. Low-scatter slits in SAXSpoint 5.0 are used as guard slits in front of the sample. The X-ray detector is a DECTRIS Eiger2 1M. The slits, sample and detector are enclosed in a vacuum chamber to reduce scattering from the air. The detector can be moved along the X-ray axis under vacuum to change the sample-to-detector distance between 53 and 1610 mm. The X-ray flux at 8.0 keV is 1.0 × 10 ¹¹ cps with a ring current of 200 mA, shortening the exposure time by nearly 1000 times compared with the original laboratory X-ray source. The purpose of employing SAXSpoint 5.0 is to provide a user-friendly SAXS/WAXD system. Anton Paar's measurement control system is employed in user operations. Many users utilize a multi-sample holder onto which 20 samples are fixed and measured in turn as programmed. The data analysis software is also provided by Anton Paar, but data can optionally be stored in TIFF format to be processed by any software that users are familiar with. Among the various sample attachments available from Anton Paar, a goniometer stage for grazing-incidence SAXS/WAXD is employed by many users.

Spintronics based on ferromagnets has enabled the development of microwave oscillators and diodes. To achieve even faster operation, antiferromagnets hold great promise despite their challenging manipulation. So far, controlling antiferromagnetic order with microwave currents remains elusive. Here we induce the coherent rotation of antiferromagnetic spins in a Weyl antiferromagnet W/Mn₃Sn epitaxial bilayer by DC spin–orbit torque. We show the efficient coupling of this spin rotation with microwave current. The coupled dynamics produce a DC anomalous Hall voltage through rectification, which we coin the antiferromagnetic spin-torque diode effect. Unlike in ferromagnetic systems, the output voltage shows minimal dependence on frequency because of the stabilization of the precession cone angle by exchange interactions. Between 10 GHz and 30 GHz, the output voltage decreases by only 10%. Numerical simulations further reveal that the rectification signals arise from the fast frequency modulation of chiral spin rotation by microwave spin–orbit torque. These results may help the development of high-speed microwave devices for next-generation telecommunication applications.

Polar metals have recently garnered increasing interest because of their promising functionalities. Here we report the experimental realization of an intrinsic coexisting ferromagnetism, polar distortion and metallicity in quasi-two-dimensional Ca₃Co₃O₈. This material crystallizes with alternating stacking of oxygen tetrahedral CoO₄ monolayers and octahedral CoO₆ bilayers. The ferromagnetic metallic state is confined within the quasi-two-dimensional CoO₆ layers, and the broken inversion symmetry arises simultaneously from the Co displacements. The breaking of both spatial-inversion and time-reversal symmetries, along with their strong coupling, gives rise to an intrinsic magnetochiral anisotropy with exotic magnetic field-free non-reciprocal electrical resistivity. An extraordinarily robust topological Hall effect persists over a broad temperature–magnetic field phase space, arising from dipole-induced Rashba spin–orbit coupling. Our work not only provides a rich platform to explore the coupling between polarity and magnetism in a metallic system, with extensive potential applications, but also defines a novel design strategy to access exotic correlated electronic states.

A method of post-acquisition upsampling for scanning x-ray microscopy is developed in this study to improve the spatial resolution beyond the Nyquist frequency as determined by the intervals of a raster scan grid. The proposed method is applicable only when the probe beam size is not negligibly small compared with the pixels that constitute a raster micrograph—the Voronoi cells of a scan grid. The unconvoluted spatial variation in a photoresponse is estimated by solving a stochastic inverse problem at a higher resolution than that at which the data are acquired. This is followed by a rise in the spatial cutoff frequency due to a reduction in the noise floor. The practicability of the proposed method was verified by applying it to raster micrographs of x-ray absorption in Nd-Fe-B sintered magnets. The improvement thus achieved in spatial resolution was numerically demonstrated via spectral analysis by using the discrete Fourier transform. The authors also argue for a reasonable decimation scheme for the spatial sampling interval in relation to an ill-posed inverse problem and aliasing. The computer-assisted enhancement in the viability of scanning x-ray magnetic circular dichroism microscopy was illustrated by visualizing magnetic field-induced changes in domain patterns of the Nd₂Fe₁₄B main-phase.