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2026.05.19

Baryon Structure Variations in Nuclear Matterwithin the Quark-meson Coupling Model

講師：Professor Miyatsu Tsuyoshi（Soongsil University, Seoul, Korea）
日時：令和8年6月８日（月）16:00-
場所：本館2階 227C 物理学系輪講室

　The quark-meson coupling (QMC) model describes nuclear many-body systems in terms of quark degrees of freedom. In this model, quarks are confined inside each baryon and interact self-consistently with scalar- and vector-meson fields generated by the surrounding nuclear medium. As a result, the internal structure of baryons changes with density, producing density-dependent effective masses and baryon-meson couplings. This mechanism offers a microscopic interpretation of nuclear saturation and provides a natural bridge between baryon structure and nuclear many-body dynamics.
　In this seminar, I will review the basic idea of the original QMC model and its applications to nuclear matter and finite nuclei, following the developments summarized in the review by Saito, Tsushima, and Thomas. I will then discuss several extensions and applications, including hyperonic matter, chiral effects, neutron-star equations of state, and the role of Fock terms and tensor couplings in dense matter. Finally, I will introduce a recent development toward quarkyonic matter, where baryonic and quark degrees of freedom coexist in a high-density regime. This talk aims to clarify how in-medium baryon structure variations can connect finite nuclei, dense matter, neutron stars, and possible quarkyonic phases within a common microscopic perspective.

連絡教員：物理学系　関澤　一之（内線2463）

https://www.phys.sci.isct.ac.jp/wp/wp-content/uploads/2026/05/443.pdf

セミナー

2026.05.19

From Nuclear Potentials to Reaction Dynamics:Application to Diverse Nuclear Reactions

講師：Dr. Heo Kyoungsu（Soongsil University, Seoul, Korea）
日時：令和8年6月８日（月）15:00-
場所：本館2階 227C 物理学系輪講室

　This talk introduces how nuclear potentials are used to understand low-energy nuclear reaction dynamics. In this energy region, reaction observables are strongly affected by nuclear structure, channel coupling, collective motion, cluster correlations, and breakup or fusion processes. Because many reaction channels can contribute coherently, a simple perturbative description is often insufficient as a complete reaction model. A practical strategy is to separate the reaction space into explicitly treated channels and effectively treated channels. The optical model potential accounts for the loss of elastic flux into non-elastic channels, while coupled-channel methods describe selected important excitations and reaction pathways more directly. Microscopic ingredients, such as folding potentials based on nuclear densities and effective nucleon-nucleon interactions, provide a useful bridge between nuclear structure and reaction observables.
　The presentation also discusses how interference among different reaction amplitudes shapes the measured cross sections. Recent visualization approaches based on scattering amplitudes offer an intuitive way to interpret near-side, far-side, internal, and barrier-related components of the reaction. Overall, the talk aims to show how phenomenological, coupled-channel, and microscopic potential models can be combined to extract physical reaction mechanisms from low-energy nuclear scattering data.

連絡教員：物理学系　関澤　一之（内線2463）

https://www.phys.sci.isct.ac.jp/wp/wp-content/uploads/2026/05/442.pdf

セミナー

2026.05.15

Optical renormalization of collective magnetic excitations in quantum materials

講師：Dr. Davide Bossini（University of Konstanz, Germany）
日時：令和8年6月1日（月）16:30-
場所：南5号館1階 103B第2会議室

　It has been proposed that magnetic waves in solids, i.e. spin waves or magnons, are promising information carriers for future information technology, enabling the processing of data at THz rates with limited energy dissipations. In this talk, I will briefly discuss how these excitations can be coupled to charges, highlighting recent progress involving processes at terahertz frequencies [1-2].
The main part of the talk will address the optical manipulation of magnons. I will show how resonant excitation of specific magnetic and electronic transitions drives the system into non-equilibrium states in which magnon modes, that are not directly excited, become activated and substantially modified. Two distinct physical scenarios will be discussed. In the first, optical excitation of electronic transitions modifies the magnetic anisotropy in a 20-nm-thick magnetic film, leading not only to the generation of coherent magnons but also to an on-demand frequency renormalization [3]. Both redshifts and blueshifts of the magnon frequency are achieved, reaching up to 40% of its equilibrium value at room temperature. In the second scenario, I will present an approach based on high-momentum magnons with wave vectors near the edges of the Brillouin zone, which can be resonantly driven using mid-infrared laser pulses. This excitation pathway activates distinct zone-center modes whose amplitudes and frequencies are strongly renormalized compared to their equilibrium values [4]. I will conclude by outlining future perspectives of this research direction, with the long-term goal of achieving arbitrary optical control over magnon dispersion relations in quantum materials.

References
[1] T. Mezger et al., Physical Review Letters 135, 076702 (2025).
[2] M. Cimander et al., Nature Communications 17, 1480 (2026).
[3] V. Wiechert et al., Nature Communications 17, 145 (2026).
[4] C. Schoenfeld et al., Science Advances 11, 25 (2025).

連絡教員：物理学系　佐藤　琢哉（内線2716）

https://www.phys.sci.isct.ac.jp/wp/wp-content/uploads/2026/05/441.pdf

セミナー
2026.05.15

Directed dispersal of bacteria swimming in confined spaces
講師：Professor Daisuke Takagi（University of Hawaii at Manoa, Honolulu, HI ）
日時：令和8年5月25日（月）10:30-
場所：南5号館5階 503CD 大会議室

Bacteria disperse over time and space through random moves and turns. The dynamics of bacteria can be significantly altered in confined spaces of relevance to their native habitats. This talk presents some recent experimental observations of bacteria swimming in confined spaces. The results show surprising phenomena featuring bacterial escapes and migration. These behavioral responses are interpreted using basic physical and hydrodynamic principles. The findings suggest that the physical landscape can profoundly impact the dynamics and distribution of bacteria.

※本セミナーは学術変革領域(A)「動的物質科学の創成量子と古典の枠を超える」との共催です。

連絡教員：物理学系　西口　大貴（内線2447）

https://www.phys.sci.isct.ac.jp/wp/wp-content/uploads/2026/05/119tokubetsu.pdf

セミナー

2026.05.01

Magnon thermal Hall effect in antiferromagnetic insulators

講師：川野雅敬助教（東京大学大学院総合文化研究科）
日時：令和8年5月18日（月）13:30-
場所：本館2階 290 物理学系輪講室

　The Hall effect is traditionally associated with the motion of charged particles subjected to an external magnetic field via the Lorentz force. Beyond this classical picture, Hall responses can also arise without an external magnetic field. In magnetic insulators, magnons, charge-neutral bosonic quasiparticles, can exhibit the thermal Hall effect through an emergent gauge field, without relying on the Lorentz force [1]. The thermal Hall effect is of fundamental importance as it provides a powerful probe of charge-neutral carriers and emergent gauge fields in quantum magnets.
In this seminar, I will discuss the realization of the magnon thermal Hall effect in two classes of systems where it was previously thought to be absent or strongly suppressed.
First, I will discuss the realization of this effect in edge-shared lattices, such as square and triangular lattices. The conventional U(1) gauge-field picture imposes a no-go condition that precludes the thermal Hall effect in these geometries [2,3]. We overcome this limitation by introducing a non-Abelian gauge-field picture, in which the noncommutativity of gauge fields generates an additional emergent magnetic flux [4,5]. This flux breaks effective time-reversal symmetry and enables the magnon thermal Hall effect even in edge-shared lattices.
Second, I will discuss the thermal Hall effect in a spin-gapped system: 1/3-plateau phase of a kagome antiferromagnet. Spin-gapped systems are generally expected to suppress low-energy transport due to the absence of mobile excitations. We demonstrate that this picture breaks down in the presence of strong geometric frustration. We observe the coexistence of two distinct types of quasiparticles: localized, magnetically neutral modes that contribute to longitudinal heat transport, and mobile magnetic excitations with topologically nontrivial bands, giving rise to a sizable thermal Hall effect [6].

References
[1] Y. Onose et al., Science 329, 297 (2010)
[2] H. Katsura et al., Phys. Rev. Lett. 104, 066403 (2010)
[3] T. Ideue et al., Phys. Rev. B 85, 134411 (2012)
[4] H. Takeda, M. Kawano et al., Nat. Commun. 15, 566 (2024)
[5] M. Kawano, Phys. Rev. B 112, L060403 (2025)
[6] H. Takeda, M. Kawano et al., submitted

連絡教員：物理学系　藤井　啓資（内線2136）

https://www.phys.sci.isct.ac.jp/wp/wp-content/uploads/2026/05/118tokubetsu.pdf

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