応用物理学輪講 I
11月7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7日(金) 16：50～18：50

Aグループ

座長
佐野　智紀
指導
教員名
小芦　雅斗　教授
座長
柴田　祐大
指導
教員名
高橋　陽太郎　准教授
発表者名 島田　祥汰
指導教員名 長谷川　幸雄　教授
発表題目（英語） Investigation of two-dimensional layered materials by scanning tunneling microscopy
要旨（英語） Scanning tunneling microscopy (STM) is a high-resolution scanning probe technique that enables atomic-scale imaging and direct measurement of local electronic states via scanning tunneling spectroscopy (STS). The rapid rise of mechanically exfoliated two-dimensional (2D) materials has opened new opportunities for STM studies. However, STM measurement requires finding a sample of several tens of micrometers while keeping the sample surface clean, which poses a technical challenge for the measurement.

In this study, we are working on van der Waals ferrimagnet Mn₃Si₂Te₆, which shows unconventional colossal magnetoresistance (CMR). Although many studies have investigated the origin of CMR, a clear understanding has not been achieved. In this seminar, I will introduce the methodology and recent advances.
発表言語 日本語
発表者名 鈴木　惠大
指導教員名 芦原　聡　教授
発表題目（英語） Development of a Broadband, High-Intensity Infrared Pulse Source for Reaction Control
要旨（英語） Multistep vibrational excitation driven by infrared pulses is expected to enable mode-selective control of chemical reactions by selectively activating specific molecular vibrations. To realize such reaction control, the development of broadband and high-intensity infrared pulse laser sources is essential.
In this presentation, I will introduce the development of an infrared pulse source that combines spectral broadening via self-phase modulation (SPM) in solid media with pulse compression using group delay dispersion (GDD) compensation. I will also describe the construction of the pulse characterization setup, which employs Fourier-transform infrared (FTIR) spectroscopy and an interferometric autocorrelator to evaluate the temporal and spectral properties of the generated pulses. Furthermore, I will discuss future prospects, in which numerical pulse optimization techniques will be incorporated to control the waveform and extend the approach toward reaction control mediated by vibrational excitation.
発表言語 日本語
発表者名 千石　竣介
指導教員名 渡辺　悠樹　准教授
発表題目（英語） Quasi-local Frustration-Free Free Fermions
要旨（英語） Frustration-free system have played a pivotal role in studies of quantum many-body systems. Recent studies have revealed that the frustration-free systems, expressed as sums of finite-range interactions or hoppings, exhibit several properties markedly different from those of frustrated models. In this presentation, the main topic is how the properties are changed by relaxing the finite size condition of interaction and allowing the exponentially/power-low decaying hoppings.  First, we show the method to decompose the model expressed as sums of finite range hopping to frustration-free systems which have exponentially/power-low decaying hoppings. By this decomposition, we show that the frustration-free systems violate the  properties that frustration-free systems, expressed as sums of finite-range interactions or hoppings.
発表言語 日本語

Bグループ

座長
白鳥　惇也
指導
教員名
石坂　香子　教授
座長
鈴木　滉平
指導
教員名
芦原　聡　教授
発表者名 田口　啓太
指導教員名 金澤　直也　准教授
発表題目（英語） Systematic study of anisotropic magnetoresistance on the short period helimagnets GdAlSi1-xGex
要旨（英語） Interplay between conduction electrons and local magnetic moments has great potential to realize future spin-based memory devices. Conventionally, spintronics has focused on ferromagnets, where the up and down spin states are treated as 0 and 1, respectively, and these two states have been controlled by the direction of the applied current. However, their response is limited to the nanosecond range, and the stray magnetic field hinders high-density integration of devices.

Recently, spintronics based on collinear antiferromagnets has been intensely studied. For example, the two states are regarded as 0 and 1, and current-induced switching of the two states has already been reported. Here, a picosecond-order fast response is realized, and antiferromagnets show no stray field; they are also robust against external fields. However, available logic states are limited to two in these ferromagnets and collinear antiferromagnets.

In this study, we introduce short-period helimagnets GdAlSi as a potential platform to realize high-density memory devices, and explore the origin of anisotropic magnetoresistance (AMR) from Q-vector alignment for enhanced reading ability in helimagnetic spintronics.

At this point, we assume that this phenomenon originates from the electronic structure, which strongly affects the transport properties. Therefore, we doped Ge into GdAlSi to change the Fermi surface and increase the carrier density, in order to observe the effects on AMR, and search the origin.
発表言語 英語
発表者名 多田　有輝
指導教員名 長谷川　達生　教授
発表題目（英語） Control of Layered Structures of Chiral Organic Semiconductors by Suppressing Steric Hinderance Effect through Heteromolecular Mixing
要旨（英語） Organic semiconductors in which alkyl groups are introduced into a π-electron framework exhibit lamellar crystallinity and are advantageous for constructing thin-film transistors. Although chiral organic semiconductors are expected to be useful owing to diverse properties arising from chirality, steric hindrance introduced by chirality within the molecular structure hinders lamellar crystallization and lowers charge-transport capability. In this study, we investigated mitigating this hindrance by mixing the chiral molecules PE-S-EH-BTBT and mono-C6-BTBT in an equimolar ratio. Differential scanning calorimetry (DSC) and powder X-ray diffraction of the prepared mixture confirmed the formation of a lamellar co-crystal with a long periodicity that is distinct from those of the individual components.
発表言語 日本語
発表者名 田中　陽帆
指導教員名 吉岡　孝高　准教授
発表題目（英語） Precision Spectroscopy of Laser-cooled Positronium
要旨（英語） Positronium (Ps) is a hydrogen-like atom consisting of an electron and a positron bound by electromagnetic interaction. Measuring the transition frequencies between its energy levels provides a stringent test of quantum electrodynamics (QED).

We are currently pursuing a precision measurement of the 1S–2S transition frequency of laser-cooled ortho-positronium. For this experiment, we are developing a high-power continuous-wave (CW) 486 nm laser for spectroscopy. The laser is locked to a linear cavity inside the vacuum chamber, and its absolute frequency is determined by a Ti:sapphire-based optical frequency comb.

In this presentation, I will introduce the design of our spectroscopic experiment, with a particular focus on the stable operation of the light source under accelerator conditions, and report on the current status and progress of the experiment.
発表言語 日本語
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