応用物理学輪講 I
10月31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10月31日(金) 16：50～18：50

Aグループ

座長
小泉　勇樹
指導
教員名
沙川　貴大　教授
座長
齊藤　孝太朗
指導
教員名
吉岡　孝高　准教授
発表者名 小川　怜恩
指導教員名 小濱　芳允　准教授
発表題目（英語） Technical Development for the Magnetocaloric Effect Measurement Under Destructive Pulsed High Magnetic Fields
要旨（英語） The magnetocaloric effect (MCE) is a phenomenon where the temperature of a magnetic material changes upon application of an external magnetic field. Since changes in magnetic entropy accompanying modifications in magnetic structure are detected as temperature changes, the MCE serves a useful probe for understanding magnetic field-induced phase transitions and for investigating the thermodynamic properties. For example, electrical-resistance measurements of Au16Ge84 thin-film thermometers [1] and dielectric-constant measurements of KTa1-xNbxO3 crystals [2] have been proposed as MCE measurement techniques up to 60 T using non-destructive pulsed magnets. However, performing MCE measurements in ultrahigh magnetic fields exceeding 100 T with the destructive methods is more challenging due to severe electrical noise and the short field duration on the order of microseconds. Therefore, we aim to improve MCE measurement techniques to achieve higher accuracy and faster response time by combining the Radio frequency electrical resistance measurement method [3] with thin-film thermometers. In this presentation, I will introduce the current status of MCE measurements and will describe the ongoing challenges for the development of new thin-film thermometers.

[1] T. Kihara et al., Rev. Sci. Instrum. 84, 074901 (2013).

[2] A. Miyake et al., Rev. Sci. Instrum. 91, 105103 (2020).

[3] T. Shitaokoshi et al., Rev. Sci. Instrum. 94, 094706 (2023).
発表言語 英語
発表者名 小椋　悠樹
指導教員名 関　真一郎　教授
発表題目（英語） Observation of a large spontaneous Hall effect in antiferromagnets with broken time-reversal symmetry
要旨（英語） Antiferromagnets with broken time-reversal symmetry have attracted significant attention, as they exhibit intriguing physical properties such as a spontaneous Hall effect induced by a fictitious magnetic field arising from the Berry curvature. Traditionally, the magnitude of the anomalous Hall effect (AHE) has been considered proportional to the magnetization of a material, and thus it was believed that the AHE would not occur in antiferromagnets. However, recent studies have revealed that the spontaneous Hall effect can indeed emerge in antiferromagnetic systems when time-reversal symmetry is broken.

In this presentation, I will explain the fundamental physical properties expected in antiferromagnets with broken time-reversal symmetry and present experimental results on magnetization and electrical transport measurements for a rare-earth alloy, which has been discovered in our laboratory as a candidate material of this class.
発表言語 日本語
発表者名 加藤　勇誉
指導教員名 十倉　好紀　卓越教授
発表題目（英語） Nonlinear transport in half-Heusler topological semimetals
要旨（英語） Nonlinear response are considered an important topic in condensed matter physics. For example, rectification effect induced by a p-n junction is essential for the modern information society. It has recently been revealed that quantum geometry plays an important role in the second-order (2f) component of the charge transport . However, conventional studies have often struggled with the direct control of material parameters. Thus, we focused on half-Heusler compounds, whose band structure can be controlled by an external magnetic field. Half-Heusler compounds are suitable for the study of nonlinear transport because ,in these systems, we can generate and control Weyl points via the application of a magnetic field. For this research, we fabricated a device using FIB to achieve a high current density and measure nonlinear transport.
発表言語 日本語
発表者名 倉持　祐希
指導教員名 井手上　敏也　准教授
発表題目（英語） Photocurrent response in a van der Waals antiferromagnet
要旨（英語） Few-layer van der Waals (vdW) crystals, which can be obtained from three-dimensional layered materials by mechanical exfoliation, are emerging material platforms for exploring the exotic transport and optical properties in atomic layer limit. Among them, few-layer vdW magnets are attracting much interest due to the versatile magnetic orderings and their controllability. In particular, unique magnetic symmetries can be realized in vdW antiferromagnets, which can be further controlled by changing thickness, applying external fields, or making vdW interfaces etc. Although antiferromagnets have no net magnetization and thus experimental probes of the magnetic order are limited, transport and optical phenomena reflecting their characteristic magnetic symmetries have been reported recently.

Here, we focus on the photocurrent response in a vdW antiferromagnet. Photocurrent potentially reflecting the antiferromagnetic order was observed in an exfoliated sample of vdW antiferromagnet. In the presentation, I will also discuss its tunability and possible origins.
発表言語 日本語

Bグループ

座長
佐藤　憩
指導
教員名
長谷川　幸雄　教授
座長
佐藤　陽紀
指導
教員名
長谷川　達生　教授
発表者名 小崎　陽友
指導教員名 山本　倫久　教授
発表題目（英語） Investigation of the competition between Kondo effect and RKKY interaction in a double quantum dot system
要旨（英語） In strongly correlated many-electron systems, it is generally difficult to treat hundreds to thousands of electrons quantum mechanically with high precision and to calculate their physical quantities accurately.
However, for the Kondo effect involving a single localized spin, a highly accurate computational method has been established using the Numerical Renormalization Group (NRG).
This suggests that a strongly correlated electron system could, in principle, be modeled quantum mechanically by considering each Kondo cloud as a fundamental building block.

The minimal structural unit in such a model is the Ruderman–Kittel–Kasuya–Yosida (RKKY) interaction between two localized spins.
Nevertheless, when the number of conduction electrons is large, no quantitative analytical method for describing the RKKY interaction has yet been fully established.

In this presentation, I introduce an experiment that observes the competition between the Kondo effect and the RKKY interaction in heavy-fermion systems, utilizing a semiconductor nanostructure in which the quantum state of conduction electrons can be controlled at the single-electron level.
The Kondo state is a spatially extended quantum-coherent state formed by conduction electrons surrounding a localized spin, within which the localized spin is completely screened by the conduction electrons.
In contrast, the RKKY interaction is an indirect exchange interaction between localized spins mediated by conduction electrons, functioning as a long-range spin–spin coupling.
When Kondo clouds overlap, the Kondo effect and the RKKY interaction compete with each other.
The experiment presented here directly observes this competition using a system composed of two quantum dots coupled through a quantum wire.
発表言語 日本語
発表者名 坂本　憲信
指導教員名 高橋　陽太郎　准教授
発表題目（英語） The magneto-optical effects in antiferromagnets and altermagnets with broken time-reversal symmetry
要旨（英語） In recent years, antiferromagnets and altermagnets with broken time-reversal symmetry have attracted significant attention as promising candidates for next-generation memory materials. These materials exhibit almost zero net magnetization and are robust against magnetic perturbations; however, the absence of sizable magnetization-proportional responses makes domain readout a major challenge.
In altermagnets, the unique magneto-birefringence effect is expected to enable domainstate discrimination through the sign of the rotation angle induced by an applied magnetic field. In this study, we attempt to experimentally demonstrate such behavior in the altermagnetic candidate Fe₂Mo₃O₈.
Furthermore, in time-reversal-symmetry-broken antiferromagnets, the magneto-optical Kerr effect originating from Berry curvature can be utilized to read out domain states via the sign of the Kerr rotation. Future work will be directed toward verifying this effect in the noncoplanar antiferromagnet GdGaI.
発表言語 日本語
発表者名 櫻田　竜河
指導教員名 武田　俊太郎　准教授
発表題目（英語） Performance Evaluation of Decoherence Suppression Using Multiple Indicators
要旨（英語） In optical quantum information processing, decoherence of photonic quantum states caused by losses in optical elements remains one of the major obstacles. One approach to suppress this decoherence involves measuring the quantum information that leaks into the environment and using the measurement results to correct the affected quantum states. Based on this proposal, we have conducted multi-round decoherence suppression experiments targeting non-Gaussian optical quantum states, and demonstrated that the negativity of the Wigner function can be improved.

However, the negativity of the Wigner function is merely one indicator of the quantum nature of a state, and is insufficient for evaluating the performance of decoherence suppression. Therefore, in addition to the Wigner negativity, we employed fidelity—an indicator of similarity to the original state—and the nullifier—an indicator of non-Gaussianity—to quantitatively analyze the effects of multi-round decoherence suppression from various perspectives. In this presentation, we report the evaluation results based on these indicators.
発表言語 英語
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