応用物理学輪講 I
11月14日
[注意事項]
発表の10日前までに　office[at]ap.t.u-tokyo.ac.jp　宛てに「氏名」「指導教員」「発表題目（英語）」「要旨（英語）」「発表言語（英語または日本語）」を送付して下さい。
発表日
2025年11月14日(金) 16：50～18：50

Aグループ

座長
鈴木　勇力
指導
教員名
十倉　好紀　卓越教授
座長
砂田　桂花
指導
教員名
中村　泰信　教授
発表者名 田中　優樹
指導教員名 Max Hirschberger 准教授
発表題目（英語） Material realization of covalent-type 3D Dirac semimetals
要旨（英語） In the previously reported 3D Dirac semimetals, the ionic bonding characters are the key to realize the Dirac semimetal states.  In these "spin-orbit type" Dirac semimetals the energy dispersions become narrow, non-symmetric along the energy direction. Here, we introduce the "covalent-type" Dirac semimetals R8CoX3, which has large, linear energy dispersion. These "covalent-type" Dirac semimetals can be viewed as the true 3D analogue of graphene, which makes this materials attractive. In this talk I introduce the current progress on this materials, including the synthesis and resistivity measurement results.
発表言語 英語
発表者名 平田　慎一郎
指導教員名 高橋　陽太郎　准教授
発表題目（英語） Photovoltaic effect via electronic excitation in multiferroics YMn2O5
要旨（英語） The bulk photovoltaic effect (BPVE) is a second order nonlinear optical effect in which light is converted into electric current in non-centrosymmetric materials. Among the microscopic mechanisms responsible for the BPVE, shift current mechanism—a photocurrent generated by the real-space displacement of photoexcited carriers associated with the Berry connection of Bloch wave functions—has attracted considerable attention in recent years. However, in multiferroics where spatial inversion symmetry is broken by spin structures, the essential characteristics of the BPVE induced by electronic excitation remain unclear.

In this study, we aim to elucidate the fundamental characteristics of the BPVE in the multiferroic YMn2O5, which exhibits two types of spin-driven polarizations originating from the inverse Dzyaloshinskii–Moriya mechanism and exchange striction mechanism, by investigating its optical response in the near-infrared to visible spectral region. Particular attention is given to clarifying how spin-driven polarization and electronic transitions respectively influence the generation of photocurrent.

This study is expected to provide insight into how spin-driven shift currents can pave the way for functional photon-charge conversion in multiferroic materials.
発表言語 日本語
発表者名 永田　利行
指導教員名 長谷川　幸雄　教授
発表題目（英語） First-principles calculation of surface states in Pb monolayer on Si(111)
要旨（英語） Measurements of vortexes using scanning tunneling microscopy and potential distribution measurements using scanning tunneling potentiometry reveal that the electron transport properties across steps on Pb monolayer films formed on Si(111) change significantly with even slight variations in Pb coverage.Therefore, in this study, first-principles calculations were performed on Pb monolayer films on Si(111) to clarify the reason for this phenomenon.Pb monolayer films on Si(111) exhibit several structures depending on the coverage ratio. Here, we focus on the Striped-incommensurate (SIC) phase (1.3 ML) and the √7×√3 phase (1.2 ML). Previous experiments have observed that the √7×√3 phase (1.2 ML) exhibits a higher resistivity at steps compared to the SIC phase (1.3 ML).Therefore, comparing these two structures is crucial.
発表言語 日本語

Bグループ

座長
滝之入　敬汰
指導
教員名
長谷川　幸雄　教授
座長
竹中　涼
指導
教員名
高橋　陽太郎　准教授
発表者名 中田　優太郎
指導教員名 香取　秀俊　教授・山口　敦史　委嘱准教授
発表題目（英語） Sympathetic cooling of thorium ions and design of an ion trap for a nuclear clock
要旨（英語） A nuclear clock is a frequency standard based on nuclear transition frequencies. Because nuclear transitions are highly insensitive to environmental perturbations, nuclear clocks are expected to achieve accuracy surpassing that of existing atomic clocks.

In particular, the transition between the nuclear ground state and the excited state of thorium-229 (Th-229) is considered the most promising reference transition for realizing such a clock, as it is the only known nuclear transition that lies within the optical wavelength range.

To realize a nuclear clock based on trapped Th-229 ions, it is essential to cool the ions and suppress their motion, since the Doppler effect caused by ion motion can shift the resonance frequency of the nuclear transition.

As a step toward cooling of Th-229 ions, we have cooled Th-232 ions to approximately 50 mK through sympathetic cooling with co-trapped Ca-40 ions.

Furthermore, for sympathetic cooling of Th-229 and Ca, we tested an ion deflector system to be used for combining Th-229 and Ca ion beams. We also designed a new ion trap for achieving a high-accuracy nuclear clock.
発表言語 日本語
発表者名 中村　俊貴
指導教員名 Gong Zongping 准教授
発表題目（英語） Quantum Complexity of Many-Body Scars
要旨（英語） Quantum resources, such as entanglement and non-stabilizerness (also known as quantum magic), play a crucial role in enabling quantum computations and measurements. Recent studies have shown that quantum complexity exhibits a hierarchical structure governed by these resources. In this presentation, we focus on quantum many-body scars (QMBS), which are non-thermal eigenstates embedded in an otherwise non-integrable and thermalizing system. We evaluate their complexity using the matrix product state (MPS) framework in order to explore the hierarchical structure of quantum complexity in many-body systems.
発表言語 日本語
発表者名 西尾　祐希人
指導教員名 井手上　敏也　准教授
発表題目（英語） Superfluid Stiffness and Flat-Band Superconductivity in van der Waals 2D Materials
要旨（英語） Zero resistance and the Meissner effect are hallmark features of superconductors, and both are governed by the superfluid stiffness, which measures the energy cost of twisting the superconducting phase. In atomically thin van der Waals (vdW) superconductors, directly measuring this quantity has been challenging; however, recent advances in microwave resonator–based devices now enable precise stiffness measurements. By combining the Hamiltonian-level tunability of vdW materials with this measurement approach, we can probe new, fundamental superconducting phenomena.

In this presentation, I will introduce several of my ongoing experiments aimed at measuring the superfluid stiffness of vdW materials. One focus is the enhancement of superfluid stiffness arising from band geometry. In the conventional BCS picture, the stiffness originates from band dispersion, so in a perfectly flat band the conventional (kinetic) contribution is expected to vanish, and superconductivity would appear to be strongly suppressed. Yet experiments on flat or nearly flat bands show that superconductivity can still emerge, suggesting that the dispersive component alone is insufficient to account for the finite superfluid stiffness observed experimentally. This has led to the identification of a geometric contribution to the superfluid stiffness, arising from the quantum geometry of the Bloch states—especially the quantum metric—which can remain finite even when the dispersion is tiny.
発表言語 日本語
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