Applied Physics
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Collaboration on bulk-edge correspondence in gapless topological > phases
To significantly progress our joint research, we will invite a researcher from the Indian Institute of Technology Bombay to engage in 11 days of in-person discussion focused on bulk-edge correspondence and in gapless topological phase and effects of disorders. We also plan to discuss future application plans aimed at continuing collaborative research.
Hideaki Obuse (researchmap.jp, scholar.google.de), Soumya Bera, Ranjith R. Kumar, and Ishita Modak
JST Sakura Science Program (B course) 2025.8.21～2025.8.31
High-harmonic generation of by topological magnon edge states
Theoretical and experimental research on high harmonic generation originating from topological edge states of magnons is conducted.
Hideaki Obuse (researchmap.jp, scholar.google.de), and Hirori Hideki
Imaging valley-vortex edge modes in a phononic crystal at ultrahigh frequencies
We perform optical measurements and numerical simulations of guided phonon propagation in novel topological phononic crystal structures at ultrahigh frequencies. The structures support valley-polarized states that exhibit an energy vortex nature and propagate with high efficiency at domain boundaries because backscattering is suppressed due to conservation of time reversal symmetry. We extract frequency- and time-resolved spatial mode patterns and -space images, together with dispersion relations. We investigate the conditions required for robust propagation along interfaces and thereby observe very high efficiency waveguiding.
Paul H. Otsuka, Motonobu Tomoda, Daiki Hatanaka, Hiroshi Yamaguchi, Kenji Tsuruta, and Osamu Matsuda
Study of Quantum Plasticity and Supersolidity of solid 4He by Observing Motion of Sinking Object
Solid helium is often referred to as quantum solid and known to deform easily and rapidly even under tiny force, strongly subjected to quantum effect. A number of research have been conducted to study its elasticity, or reversible deformation, but its plasticity, or irreversible deformation, is scarcely understood. In the proposed experiment, we are going to precisely measure the motion of objects sinking in solid helium to elucidate the quantum effects on the plasticity of solid helium. Especially, the local superflow expected to exist in cores of dislocations and grain boundaries are to be examined, in the context of supersolidity.
Grant-in-Aid for Early-Career Scientists 2025.4.1～2028.3.31
Novel continuous-time crystallinity observed in a superfluid dripping system
While the dripping period of a classical viscous fluid is widely distributed due to the influence of chaos, the dripping period of a superfluid 4He liquid is discretized to a constant value specified by integers even if the inflow rate changes. We clarify that this robust discretization is the realization of a continuous-time crystal from the viewpoints of inflow rate phase diagram, temperature phase diagram, wall shape and dimensionality, and time-domain phonon excitation.
Ryuji Nomura, Tomoyuki Tani, and Yuki Aoki
Grant-in-Aid for Scientific Research(B) 2025.4.1～2028.3.31
Nucleation probability of methane + propane mixed-gas hydrate depending on gas composition
Natural gas hydrate contains large amounts of natural gas and is attracting attention as one of the future domestic resources, or as its storage and transportation medium. For its industrial use, it is one of the problems that the nucleation process is difficult to control. This study has revealed that the nucleation probability of methane + propane mixed-gas hydrate, as a mimic of natural-gas hydrate, depends on the composition. This result will help develop technology for industrial use of gas hydrates.
Tsutomu Uchida, Masato Hayama, Motoi Oshima, and Kenji Yamazaki
Photoinduced Metal–Insulator Phase Separation Depending on the Conformational Order of Molecules in β-(BEDT-TTF)₂I₃
In this study, the role of the conformational order of organic molecules in photo-induced phase separation (PIPS), which forms the basis for ultrafast switching devices, is investigated. The results show that PIPS occurs below 150 K in the partially ordered phase and below 75 K in the homogeneously ordered phase. This result implies that conformational order plays a crucial role in determining the temperature at which PIPS occurs, providing significant insight for room-temperature operation, which is essential for the practical application of devices.
Kensho Nagata, Satoshi Tsuchiya, Koichi Nakagawa, Hiromi Taniguchi, and Yasunori Toda
Lack of Oscillatory Motion of Superfluid ⁴He During its Dripping from a Needle
Although pendant droplets commonly exist in our daily lives, their dynamics are not fully understood. To obtain further understanding of its physics, we observed superfluid helium dripping from a thin needle by a high-speed camera. Superfluidity is an inviscid liquid state only happening in helium at low temperatures. The present study where we used a thin needle to eliminate the droplet’s remnant volume clearly demonstrated that the dissipation-less large oscillation observed in the previous experiments was crucial for the discretization of the dripping period which is novel phenomenon reflecting the anomalous fluid properties of superfluid helium.
Tomoyuki Tani, Keigo Sawada, Keito Miyake, Shota Takamatsu, Ryota Yamane, Yuri Ishimoto, Ryuta Matsukawa, Yuki Aoki, and Ryuji Nomura