-
セミナー
2026.07.10
講師：Dr. Oh Changgeun （東京大学 大学院工学系研究科 物理工学専攻）
日時：令和8年7月27日（月）15:30-
場所：本館2階 227C 物理学系輪講室Quantum geometry, which describes the geometric structure of Bloch wave functions in momentum space, has emerged as a key research topic in condensed matter physics. While the Berry curvature has been extensively studied for its role in determining topological properties, the influence of the quantum metric or quantum distance on material properties has only recently gained significant attention. This presentation explores the impact of quantum geometry on various material properties, focusing on the following aspects:
1. Mass-Invariant universal optical conductivity: In isotropic quadratic band touching semimetals, the optical conductivity is universally given by a geometric quantity independent of the detailed band structure.
2. Bulk-interface correspondence in singular flat band systems: Bulk-edge correspondence is a fundamental concept in topological physics. While previous studies have focused on the topological properties of wave functions in relation to boundary modes, we demonstrate that another geometric quantity—the quantum distance—can also establish a bulk-interface correspondence in singular flat band systems.
3. Third harmonic generation of Higgs mode in superconductor: Collective modes in superconductors, such as the Higgs mode, offer deep insights into the nature of condensates. Third-harmonic generation is a primary tool for probing the Higgs mode, but its signal competes with that of quasiparticle excitations depending on impurity scattering rates.
In particular, in the clean regime the standard BCS theory generally predicts the dominance of quasiparticle contributions. Here, we propose and demonstrate that the quantum geometry of electronic bands can be a key mechanism governing this competition.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/2026/07/447.pdf
-
セミナー
2026.06.29
講師：Dr. Flavio Ronetti（Aix Marseille University, France）
日時：令和8年7月7日（火）13:30-
場所：本館1階 M112 講義室Anyons, quasiparticles with exchange statistics intermediate between bosons and fermions, are among the most distinctive excitations of fractional quantum Hall systems. Their fractional charge has long been accessed through shot-noise measurements at quantum point contacts, but a direct and robust detection of their braiding statistics remains a central challenge. In this seminar, I will discuss several transport-based approaches to probing anyonic properties in fractional quantum Hall edge states.
First, I will show how the finite spatial width of anyons can strongly affect braiding-induced transport signatures, even when this width is extremely small. This effect is especially relevant for hierarchical states and provides a possible explanation for recent experiments at filling factor (ν=2/5). I will then discuss
photo-assisted shot noise as a tool to identify multiple tunneling charges in states with several edge modes, focusing on the case (ν=2/3), where different quasiparticle charges may tunnel simultaneously at a quantum point contact.
Finally, I will present proposals for directly measuring the anyonic statistical angle using controlled time-dependent transport. These setups rely on anyons emitted from a QPC source and braided either around a fractional quantum Hall droplet or through a closed-loop geometry on a single chiral edge. In these schemes, the time-dependent current and current cross-correlations carry signatures governed by the statistical phase, while suitable protocols allow the extraction of the anyonic angle without requiring independent knowledge of non-universal parameters. Together, these results highlight how edge transport can provide experimentally accessible and theoretically sharp probes of fractional charge, braiding, and anyonic statistics.
The following published papers are related to this work:
https://arxiv.org/abs/2311.15094
https://arxiv.org/abs/2502.15909
https://arxiv.org/abs/2503.17008
https://arxiv.org/abs/2506.09774連絡教員：物理学系 藤澤 利正（内線2750）
https://www.phys.sci.isct.ac.jp/wp/wp-content/uploads/2026/06/446.pdf
-
セミナー
2026.06.24
講師：Professor Sven van Teeffelen（The University of Montreal, Montreal, CANADA ）
日時：令和8年7月1日（水）13:30-
場所：南5号館5階 503CD 大会議室 および Zoom*All living cells are bounded by envelopes that protect them from the environment and confer their sizes and shapes. These shapes help cells to spatially organize their internal biological processes, allowing them to divide and faithfully segregate genetic material to each daughter. Yet, we still know very little about how cells obtain and control cell shape, even in the arguably simplest and best understood organism: the rod-shaped Escherichia coli.
To resist a high intracellular osmotic pressure, bacteria and many other single-celled organisms are surrounded by a cell wall, an elastic, covalent meshwork of sugars and peptides. For walled cells to grow, they must enzymatically cut cell-wall bonds while inserting new cell-wall material to prevent envelope rupture. How do cells control a straight rod-like cell geometry with a well-defined diameter, while also maintaining cell-wall integrity and increasing cell length at a rate that accommodates biomass growth? We have made important progress in the past two decades.
Here, I will present two related vignettes that answer aspects of these questions in Gram-negative rod-shaped bacteria: First, I will present experiments showing that cells couple the global rate of envelope growth to metabolism, i.e., they increase their envelope in proportion to the production of biomass, likely at the level of the outer membrane. Second, I will present how mechanical forces and envelope curvature contribute to the regulation of cell shape locally, through cytoskeletal proteins and autolytic enzymes, based on coarse-grained computer simulations.※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。
＊本 ZOOM セミナーに参加されます場合には、事前に下記より登録を済ませてください。https://zoom.us/meeting/register/_HDG8eelQfa4fMUVRtLP3A
当日会場にお越しいただけます方は、登録不要ですので、是非、対面でご参加ください。
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/2026/06/445.pdf
-
セミナー
2026.06.02
【開催日変更】
講師：Dr. Ho Hsiao（Center for Computational Sciences, University of Tsukuba）
日時：令和8年6月24日（水）16:00-
場所：本館2階 290 物理学系輪講室In the context of Composite Higgs Models, where the standard model Higgs is interpreted as a pseudo Nambu-Goldstone Boson emerging from a new strong sector, baryons formed by matters in different representations, known as chimera baryons, could serve as top partners. The chimera baryon sharing the same quantum number as the top quark can mix with it, effectively lifting the mass of the top quark. We report our results of the spectrum of low-lying chimera baryons in the quenched approximation on a Sp(4) gauge theory. We perform spin and parity projections to separate the states and study their mass hierarchy. Particularly, we investigate the chiral extrapolation of chimera baryon masses. To accomplish this, we use a fitting function inspired by QCD chiral Effective Field Theory (EFT). Lastly, we present our current results using the dynamical fermions. 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/2026/06/120tokubetsu-henkou.pdf
-
セミナー
2026.05.28
講師：Dr. Alexis Poncet（CNRS, Laboratoire de physique à l'ENS de Lyon, Lyon, France ）
日時：令和8年6月8日（月）10:30-
場所：南5号館5階 503CD 大会議室 および Zoom*In systems far from thermal equilibrium, structure and dynamics are intertwined, leading to emergent phenomena such as collective motion in active matter or anomalous wave propagation in nonreciprocal systems. This talk explores the role of microscopic interactions in shaping these behaviors: What forms do they take? What are their consequences at macroscopic scales? And how can we infer them from experiments?
In the first part, I will present a study of self-propelled Janus particles (developed in the Nishiguchi lab), which exhibit coherent flocking at the collective level. Using a recent framework known as Stochastic Force Inference, we learned the microscopic interactions between particles [1]. These interactions not only reproduce experimental observables in simulations but also reveal a mechanism for flocking: pairwise torques that cause particles to turn away from their neighbors.
The second part focuses on flowing droplets with nonreciprocal hydrodynamic interactions, where left/right asymmetry gives rise to unexpected dynamics. Despite being overdamped, a 1D stream of such droplets supports nonlinear waves due to nonreciprocal coupling. Theoretically, we predict solitary waves described by the Korteweg–de Vries (KdV) equation (or KdV-Burgers with damping) [2]. A physics-informed neural network further uncovers this dynamics directly from experimental data.
If time permits, I will briefly discuss two ongoing theoretical projects on active and nonreciprocal systems: (1) how memory effects in viscoelastic media alter Motility-Induced Phase Separation of active particles, and (2) how Kardar-Parisi-Zhang fluctuations are evidenced in a 1D lattice model with nonreciprocal interactions.
[1] Hem, Poncet, Ronceray, Nishiguchi & Démery, Soft Matter 21 (37), 7257-7269 (2025)
[2] Colen, Poncet, Bartolo & Vitelli, Physical Review Letters 133 (10), 107301 (2024)
※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。
＊Zoom 登録リンク：https://zoom.us/meeting/register/qw3pWA-kTjW7F01RXWqJSg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/2026/05/121tokubetsu.pdf
-
セミナー
2026.05.22
講師：鈴木 史花 氏（東京大学 素粒子物理国際研究センター）
日時：令和8年6月10日（水）13:30-
場所：本館2階 290 物理学系輪講室The Kibble–Zurek mechanism (KZM) combines Kibble’s observation of topological defects formation in cosmological phase transitions with Zurek’s theory relating their density to critical slowing down, and hence to the universality class of a second-order phase transition. The resulting KZM predicts defect density as a function of the quench rate in second-order phase transitions, in both classical and quantum settings. It has applications across a wide range of fields, including condensed matter physics, cosmology, and quantum computing.
In this talk, I will discuss extensions of KZM beyond its original formulation. I will show how KZM can be combined with nucleation theory to describe weakly first-order phase transitions, how nonadiabatic excitation formulas can be generalized to exotic quantum phase transitions, and how order-parameter dynamics offers a new perspective on KZM. I will also discuss how machine learning can provide deeper insight into second-order phase transitions beyond the conventional KZM framework.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/2026/05/444.pdf
-
セミナー
2026.05.19
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
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
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
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
