"This work was inspired by a simple question. Conventional measurements only reveal averaged chirality, but what does the actual spatial distribution look like? We wondered whether directly visualizing chirality as an image could provide deeper insights, which motivated us to pursue this research," says Professor Katsuhiko Miyamoto (Chiba University).

To generate regions with different chirality in the same material, the researchers built a moiré-type metasurface by stacking microscopic silver disk patterns with a slight offset or rotation. These structures were fabricated at the micrometer scale so that they could strongly interact with THz light. By carefully designing the overlapping patterns, the researchers created an artificial surface containing both right-handed and left-handed twisting regions, allowing them to create and control different chiral configurations in a designed system.

When circularly polarized THz waves were directed onto the metasurface, different regions responded differently depending on their local chirality. The new approach could spatially resolve chirality distributions with a resolution of approximately 100 μm, roughly the thickness of a human hair.

"We succeeded in visualizing the coexistence of different chirality within a single sheet for the first time in the world. These findings are expected to find applications in the quality evaluation of next-generation materials, the analysis of biomolecular structures, and the development of new THz devices," says Miyamoto.

As advances in nanofabrication make increasingly sophisticated chiral materials possible, the proposed method could provide a reliable way to examine whether these structures function as intended without damaging the material.

Looking ahead, the researchers expect to expand the technology to a broader frequency range from 2 to 15 THz, enabling more detailed structural analyses. The approach could eventually support new diagnostic techniques for visualizing abnormal protein aggregates linked to disease, help inspect advanced signal-control devices for next-generation communication systems such as Beyond 5G and 6G, and detect subtle distortions inside quantum and soft materials.

Publication Details:
Title: Multiscale chirality in moiré metasurfaces revealed by terahertz circular dichroism spectroscopic imaging
Authors: Uina Chiba, Shota Tsuji, Gaku Oritani, Takumi Yoichi, Rinpei Sasaki, Takeo Minari, Seigo Ohno, and Katsuhiko Miyamoto
Journal: ACS Photonics
DOI: 10.1021/acsphotonics.6c00372

Contact:
Seigo Ohno
Graduate School of Science, Department of Physics, Tohoku University,
Email: seigo* tohoku.ac.jp
Website: https://sites.google.com/view/tohoku-quonptumics/

One of the biggest mysteries lies within the Atotsugawa Fault System in Japan. What makes the area unusual is that, despite being in a tectonically active region where Earth's plates are constantly shifting, it does not produce as many large earthquakes as other major faults.

(Top) Geological map of the Atotsugawa Fault System. (Bottom left) Depth section of hypocenters from 1998-2025 along the Atotsugawa Fault System. (Bottom right) Frictional properties of graphite and graphene oxide. G-Q represents mixtures of graphite and quartz with different volume percentages of graphite. Orange and blue arrows represent shearing along the basal plane and interlayer delamination, respectively. ©Tomoya Shimada et al.

A group of researchers at Tohoku University has shed light on an unknown aspect of the Atotsugawa Fault System, revealing why earthquakes are unusually rare there. Using an innovative approach that combines advanced analytical techniques such as Raman spectroscopy, X-ray photoelectron spectroscopy (XPS), and Transmission Electron Microscopy (TEM), they made an intriguing discovery: a single layer of graphene oxide found within this active fault may be the key to solving this mystery.

TEM images of graphene oxide in the fault gouge (excerpt). (Left) TEM image of a foil sample cut across a microcrack within the fault gouge (the darker region on the left consists of quartz and clay minerals, while the right side shows carbonaceous material filling the crack, including graphene oxide). The inset shows a Selected Area Electron Diffraction (SAED) pattern collected from location 7 in the TEM image. (Right) High-resolution TEM (HRTEM) image showing graphene oxide nanoparticles. The insets show fast Fourier transform (FFT) patterns from regions I, II, and III. The yellow dashed regions contain distinct lattice fringes with a spacing of d = 0.21 nm, corresponding to the (100) plane of graphene. ©Tomoya Shimada et al.

What makes this discovery particularly significant is that graphene oxide, widely used in cutting-edge technology and typically produced synthetically, has not been observed naturally in such an ultrathin form before. In this setting, it exhibits unique properties, including an extremely smooth surface that leads to very low friction. The presence of this natural lubricant may help explain why some faults move slowly and steadily rather than causing sudden earthquakes.

In their research, the team focuses on two key mechanisms that reduce friction in faults. First, oxygen-containing groups in graphene oxide interact with water molecules, creating lubricating conditions. Second, graphene oxide nanosheets slide between minerals in the fault, reducing friction even more.

"We believe that when faults move, they trigger chemical reactions that create graphene oxide. In other words, the more a fault slips, the more it generates its own 'nano-lubricant,' which helps the fault move even more easily," said Professor Hiroyuki Nagahama.

This study suggests that graphene oxide can remain stable under the temperature conditions present at depths where slow fault slip occurs. This implies that once formed, it may continue to act as a natural lubricant over long periods of time, influencing how stress is released along the fault. These findings highlight the previously unrecognized role of carbon-based materials in regulating fault behavior.

"If graphene oxide can form naturally in faults, it opens up entirely new possibilities--not only for understanding earthquake behavior, but also for exploring how faults evolve over time" said Tomoya Shimada, a member of the research team from the Department of Earth Science at Tohoku University.

Schematic view ©Tomoya Shimada et al.

Ultimately the discovery elucidates more about fault behavior while also highlighting the power of interdisciplinary research to uncover hidden processes within the Earth. Studies like these, which bridge the gap between geoscience, materials science, and tribology, have the potential to fundamentally transform how carbon is studied on Earth. As research continues, these approaches may help deepen our understanding of earthquake processes and how faults behave deep underground.

Publication Details:
Title: Ultra-low friction graphene oxide in the Atotsugawa Fault System
Authors: Tomoya Shimada*, Hiroyuki Nagahama, Jun Muto, Norihiro Nakamura, Sando Sawa, Hiroaki Ohfuji
Journal: Nature Communications
DOI: 10.1038/s41467-026-72239-5

Contact:
Hiroyuki Nagahama
Graduate School of Science, Department of Earth Science, Tohoku University,
Email: hiroyuki.nagahama.c7 * tohoku.ac.jp
Website: https://researchmap.jp/read0011068

Tomoya Shimada
Graduate School of Science, Department of Earth Science, Tohoku University,
Email: tomoya.shimada.s2 * dc.tohoku.ac.jp

Details of the researchers' findings were published in the journal Nature Chemistry on April 23, 2026.

Hydrogen is widely regarded as a promising clean energy source because it produces only water when used as fuel. Among the various methods for producing hydrogen, photocatalytic overall water splitting--using sunlight to split water into hydrogen and oxygen--has attracted increasing attention as an environmentally friendly and sustainable approach.

In photocatalytic systems, a photocatalyst absorbs light energy and drives the chemical reactions needed to split water. However, the two key reactions involved--the hydrogen evolution reaction and the oxygen evolution reaction--are often slow on the photocatalyst surface. To improve efficiency, researchers typically modify photocatalysts with cocatalysts that help promote these reactions.

Conventional photocatalytic systems are complex. Separate cocatalysts are usually required to promote hydrogen and oxygen evolution, and they must be carefully positioned on the photocatalyst surface. In addition, an oxygen-blocking layer is often added to prevent reverse reactions that reduce oxygen and lower overall efficiency. These complicated structures make large-scale production and long-term operation more challenging.

To overcome these limitations, scientists have long sought an "all-in-one" cocatalyst--a single material capable of promoting both hydrogen and oxygen evolution reactions while preventing the unwanted reverse reaction. Until now, such a system had not been achieved because most cocatalysts have been limited to metals and metal oxides designed to promote only one type of reaction.

Schematic illustration on photocatalytic OWS.

A research group led by Ryota Sakamoto from Tohoku University's Graduate School of Science, together with graduate student Jingyan Guan, Hajime Suzuki, and Ryu Abe of Kyoto University, discovered that a conductive two-dimensional metal-organic framework known as Co-HHTP can function as an all-in-one cocatalyst.

The researchers modified the surface of an aluminum-doped strontium titanate photocatalyst (SrTiO₃:Al) with nanodomains of Co-HHTP using a simple one-step self-assembly method. The resulting material achieved stable overall water splitting without the need for an additional oxygen-blocking layer and demonstrated an apparent quantum efficiency of 31.5% at a wavelength of 350 nanometers.

"This work shows that a single material can efficiently promote both hydrogen and oxygen evolution while suppressing the reverse reaction," said Sakamoto. "By simplifying the cocatalyst design, we hope this concept will help accelerate the development of practical technologies for producing clean hydrogen from sunlight and water."

(a) OWS photocatalytic system using existing cocatalysts, and (b) OWS photocatalytic system using the all-in-one cocatalyst pursued in this study.

Beyond the performance results, the study introduces a new scientific concept in photocatalysis. The team demonstrated how conductive two-dimensional metal-organic frameworks, with properties such as electrical conductivity, molecularly defined structures that control reaction selectivity, and intrinsic porosity, can be rationally designed to perform multiple catalytic roles in a single material.

The findings also provide promising insights for real-world applications. The all-in-one cocatalyst uses inexpensive metal ions and organic ligands and avoids precious metals or toxic chromium often used in conventional systems. Combined with its simple one-step fabrication method, this new "all-in-one cocatalyst" paradigm could help advance practical technologies for sustainable hydrogen production and contribute to the realization of a future hydrogen society.

Co-HHTP, a type of conductive 2D-MOF. (a) Chemical structure of the 2D-MOF layer of Co-HHTP. (b) Stacking structure of Co-HHTP.

Publication Details:
Title: Two-dimensional metal-organic frameworks offer all-in-one cocatalysts for photocatalytic overall water-splitting
Authors: Jingyan Guan, Hajime Suzuki*, Kazuhide Kamiya, Takashi Harada, Adachi Rintaro, Osamu Tomita, Hirofumi Kurokawa, Daisuke Unabara, Koji Yonekura, Naoya Fukui, Hiroaki Maeda, Kunihisa Sugimoto, Yuichi Yamaguchi, Akinori Saeki, Akira Yamakata, Akihiko Kudo, Ryu Abe*, Ryota Sakamoto*
Journal: Nature Chemistry
DOI: 10.1038/s41557-026-02133-6

Contact:
Ryota Sakamoto
Department of Chemistry, Graduate School of Science, Tohoku University
Email: ryota.sakamoto.e3 * tohoku.ac.jp (Replace * with @)
Website: https://web.tohoku.ac.jp/sakutai/publication.html

Now, a research team led by Hiroki Karyu, Takeshi Kuroda, and Naoki Terada of Tohoku University, in collaboration with the Royal Belgian Institute for Space Aeronomy, has finally solved the mystery. Using a state-of-the-art microphysical model, the team showed that the lower haze is formed from cosmic dust - tiny particles left behind by "shooting stars" that constantly rain down on Venus.

"When we traced the life cycle of these particles in our simulations, everything suddenly fit together," said Karyu. "Cosmic dust, which might seem insignificant, turns out to be the missing ingredient needed to explain Venus's lower haze."

The formation mechanism of the lower haze. Cosmic dust entering from space is incorporated into sulfuric acid clouds. As sulfuric acid evaporates at the cloud base, the dust particles remain and coagulate to form the lower haze. ©Hiroki Karyu et al.

According to the study, incoming cosmic dust burns up high in the atmosphere, producing nanometer-sized mineral particles (Fig. 1). These particles become embedded within Venus's sulfuric acid clouds. As they drift downward into the hotter lower atmosphere, the sulfuric acid evaporates, leaving behind solid mineral cores. These cores then collide and stick together, forming the haze layer observed by past missions such as Venera and Pioneer Venus. The model's results closely match measurements collected decades ago, lending strong support to the team's conclusions.

The researchers also found that these cosmic particles play an important role in Venus's climate. Acting as "seeds" for cloud formation, they increase cloud production by an estimated 20-30% (Fig. 2). In addition, the team suggests that metallic elements within the dust, such as iron, may be responsible for the long-mysterious "unknown UV absorber" in Venus's atmosphere, a substance that strongly absorbs sunlight and affects the planet's energy balance.

"These findings show that material from space is not just a passive visitor," said Terada. "It can actively shape a planet's atmosphere and climate."

The study reshapes how scientists think about planetary atmospheres, suggesting that similar processes may occur on gas giants like Jupiter and Saturn, as well as on distant exoplanets. The team hopes to test their predictions with future missions, including NASA's DAVINCI mission to Venus, scheduled for launch in the late 2020s.

Calculated cloud mass density distribution. The solid line represents the study's model, which accounts for cosmic dust influx, showing a high degree of accuracy when compared to the Pioneer Venus (PV) probe data (dotted line). ©Hiroki Karyu et al.

Publication Details:
Title: A cosmic origin of Venus' lower haze
Authors: Hiroki Karyu*, Takeshi Kuroda, Anni Määttänen, Arnaud Mahieux, Sébastien Viscardy, Naoki Terada, Séverine Robert, Ann Carine Vandaele, Michel Crucifix
Journal: Nature Astronomy
DOI: 10.1038/s41550-026-02843-4

Contact:
Hiroki Karyu
Graduate School of Science, Tohoku University
Current affiliation: Earth-Life Science Institute (ELSI) at Institute of Science Tokyo
Email: karyu * elsi.jp (Replace * with @)
Website: https://www.researchgate.net/profile/Hiroki-Karyu?ev=hdr_xprf

But until recently, the fundamental properties of the skyrmion remained a mystery to researchers. In a paper published in Nature Communications on April 13, 2026, researchers shared new details and properties about these structures.

"Skyrmions are highly stable and move with minimal electrical current, paving the way for next-generation memory with extremely low power consumption. It's the ultimate miniaturization, utilizing 'world-class' 2-nanometer structures will allow ultra-high-density data storage and much smaller electronic devices," said Kosuke Nakayama, a professor at Tohoku University in Sendai, Japan.

Previously, researchers believed that skyrmions could only form on asymmetric crystal structures. But these tiny skyrmions, which are around 2 nanometers in diameter, are found on centrosymmetric materials like Eu(Ga,AI)₄. To understand these structures and how they form with their vortex structure, precise composition-controlled crystals of Eu(Ga,AI)₄ were synthesized and then investigated with an angle-resolved photoemission spectroscopy (ARPES).

When observing the skyrmion-host centrosymmetric material, researchers saw an important trigger that helped form the skyrmion: a Lifshitz transition, which is a sudden change in electronic states. When this change in electronic states happens, it produces overlapping Fermi surfaces or nesting Fermi surfaces. "This is like a design blueprint, acting as the precise structural blueprint for skrymion size and arrangement," said Nakayama.

Researchers also definitively answered the question of what creates the skyrmion vortices, challenging what was previously theorized about these structures. It is an interaction called the RKKY interaction, which is an abbreviation of Ruderman-Kittel-Kasuya-Yosida interaction. Previously it was assumed that a different interaction called the Dzyaloshinskii-Moriya interaction. The RKKY interaction, powered by conduction electrons, explains the nesting Fermi surfaces, the lattice structure, and the tiny size of the skyrmion.

Understanding the Lifshitz transition, the RKKY interaction, and how the magnetic material is able to develop a skyrmion, has important implications for nanocomputing. "This shift allows scientists to 'design' magnetic properties at will by manipulating electronic foundations, rather than relying on trial and error," said Nakayama.

In order for this study to come to fruition, two different labs had to work closely together to make the experiment a success. "The breakthrough in this study was made possible by the synergy between the Kyoto Sangyo University group, which synthesized the high-quality single crystals with precise composition control, and the Tohoku University group, which performed the advanced SX-ARPES experiments," said Nakayama.

Looking ahead, researchers are looking to all the different ways they can utilize skyrmion for nanocomputing, from manipulating electronic states to create skyrmions in different sizes and shapes to controlling material structure to create even smaller structures. "A key goal is to develop new materials that can operate at higher temperatures, which is essential for making these ultra-power-saving devices practical for everyday use," said Nakayama. "We will utilize the 'design blueprint' identified in this study--specifically the relationship between Fermi surface nesting and magnetic structures--to guide future material development."

(a) Schematic of magnetic skyrmion with an exceptionally small diameter. (b) Crystal structure of Eu(Ga,Al)₄. (c),(d) Schematic illustrations of field-induced rhombic and square skyrmion-lattice states. ©Yuki Arai et al.

Composition-dependent ARPES intensity maps measured for Eu(Ga,Al)₄. Red, blue, and green lines are guides for the eyes to trace the experimental Fermi surfaces h1, e2, and e1, respectively. The change in the Fermi surface (i.e., the appearance/disappearance of e1 Fermi surface) between EuGa4 and Eu(Ga_0.62Al_0.38)₄ signifies a Lifshitz transition. ©Yuki Arai et al.

Schematic of the skyrmion formation mechanism. Lleft panel is reproduction of Fig. 1(a). Right panel shows a magnified view of the four spins circled in left panel. The orientations of these spins (indicated by blue and light blue arrows) are governed by the RKKY interaction mediated by conduction electrons (green shade). ©Yuki Arai et al.

Publication Details:
Title: Origin of multiple skyrmion phases in EuAl4
Authors: Yuki Arai, Kosuke Nakayama*, Asuka Honma, Seigo Souma, Daisuke Shiga, Hiroshi Kumigashira, Takashi Takahashi, Kouji Segawa*, and Takafumi Sato*
Journal: Nature Communications
DOI: 10.1038/s41467-026-71020-y

Contact:
Kosuke Nakayama, Takafumi Sato
Tohoku University
Email: k.nakayama * arpes.phys.tohoku.ac.jp, t-sato * arpes.phys.tohoku.ac.jp (Replace * with @)
Website: https://arpes.phys.tohoku.ac.jp/index-e.html

One of the major challenges for ground-based astronomical observatories such as the Subaru Telescope on Maunakea, Hawaii is turbulence in Earth's atmosphere. As starlight passes through the atmosphere, it is distorted by turbulent air--similar to the shimmering effect seen above a hot surface--causing stars to appear blurred. Adaptive optics is a technology designed to correct this problem. It measures atmospheric distortions in real time and rapidly adjusts the shape of a special mirror to cancel them out, allowing telescopes to produce much clearer views of the universe.

Traditionally, a single artificial laser guide star is created by projecting a laser beam into the upper atmosphere, and the atmospheric turbulence is measured using this as a reference star. A newer technique known as laser tomography adaptive optics employs a constellation of four laser guide stars in the sky. By analyzing the incoming light from these guide stars, the system can reconstruct a three-dimensional model of atmospheric turbulence and apply more optimal corrections. This technique enables sharper views of the universe than is possible with a single laser guide star.

Details of the test observations are available on the website of the Subaru Telescope, National Astronomical Observatory of Japan. (LINK)

Figure 1: Schematic diagram of atmospheric turbulence correction using laser guide stars. The left panel shows the case with one laser guide star, while the right panel shows laser tomography adaptive optics using four laser guide stars. Green lines represent light from the observed celestial object, and orange lines represent light from laser guide stars created at an altitude of about 90 km. Gray disks represent atmospheric layers through which the starlight passes (upper layer around 10 km, middle layer around 5 km, and ground layer near the surface). Using four laser guide stars expands the regions where atmospheric turbulence can be measured (hatched disks) and allows turbulence at different altitudes to be reconstructed separately. (Credit: Masayuki Akiyama)

Contact:
Masayuki Akiyama
Astronomical Institute, Tohoku University
Email: akiyama * astr.tohoku.ac.jp (Replace * with @)
Website: https://www.astr.tohoku.ac.jp/en/index.html