応用物理学輪講 I
10月18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
2024年10月18日（金）16：50～18：50

Aグループ

座長
片岡　大輔
指導
教員名
川﨑　雅司　教授
発表者名 石岡　陸
指導教員名 関　真一郎　准教授
発表題目（英語） Spontaneous Hall effect and spontaneous Nernst effect in antiferromagnetic materials with broken time-reversal symmetry
要旨（英語） Traditionally, magnetic memory has utilized the magnetization of ferromagnetic materials to store information. However, recent research has shown that antiferromagnetic materials, in systems where time-reversal symmetry is broken, can also be used for magnetic memory and offer advantages over ferromagnetic materials in terms of miniaturization potential and response speed. Furthermore, in such antiferromagnetic materials, virtual magnetic fields appear, and it is predicted that they will exhibit responses such as the spontaneous Hall effect, which are equivalent to or even surpass those caused by the magnetization of ferromagnetic materials.
In this presentation, I will explain these antiferromagnetic materials with broken time-reversal symmetry, focusing on the spontaneous Hall effect and spontaneous Nernst effect, and discuss specific examples such as CoTa₃S₆ and CoNb₃S₆.
発表言語 日本語
発表者名 岩垣　貴祐
指導教員名 金澤　直也　准教授
発表題目（英語） Evaluation of nonreciprocal transport at the interface between FeSi and heavy metals
要旨（英語） Rashba spin-orbit coupling (SOC), which emerges at surfaces or interfaces with broken inversion symmetry, provides a promising platform for various spintronic phenomena such as charge-to-spin conversion and spin-orbit torque. Conventionally, achieving large Rashba splitting relies on utilizing heavy elements with strong atomic SOC. However, a recently discovered surface state in the nonmagnetic insulator FeSi derived from Zak phase, exhibits a Rashba splitting of 35 meV without heavy elements, suggesting new possibilities for designing electronic states.

In this study, we fabricated interfaces between FeSi and Group 10 elements (Ni, Pd, Pt) and investigated the influence of atomic number on Rashba SOC by measuring nonreciprocal transport. Our findings reveal that the size of Rashba SOC and the consequent nonreciprocal resistance do not necessarily correspond to the atomic number of the capping material.

In this presentation, we will show the experimental details of the magnetic properties and nonreciprocal transport in these heterostructures and discuss mechanisms responsible for the heterostructure effects on nonreciprocal transport.
発表言語 日本語
発表者名 植田　大雅
指導教員名 金澤　直也　准教授
発表題目（英語） Enhanced non-reciprocal transport phenomena at polar hetero-interfaces of novel magnetic Weyl semimetals
要旨（英語） Nonreciprocal electrical transport, where magnetoresistance depends on the direction of electric current, arises in systems that break both time-reversal and spatial-inversion symmetries. Recently, giant nonreciprocal magnetoresistance has been observed at the surfaces or interfaces of magnetic topological insulators, drawing significant attention to the potential for magnetically-controlled rectification effects.

One promising approach to achieving nonreciprocal transport is through the fabrication of pn junctions in ferromagnetic materials, which inherently break both time-reversal and spatial-inversion symmetries. However, the development of such systems has been constrained by challenges related to carrier control and tunability.

In this presentation, we will introduce candidate materials that exhibit a novel, carrier-tunable ferromagnetic Weyl semimetal phase. By fabricating pn junctions of ferromagnetic Weyl semimetals, we have achieved enhanced nonreciprocal resistance, offering new opportunities for exploring nonreciprocal transport in engineered systems.
発表言語 日本語

Bグループ

座長
川本　知輝
指導
教員名
香取　秀俊　教授
発表者名 岡村　圭太
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） Development of Nuclear Clocks Using Triply Charged thorium-229 in a Trap
要旨（英語） Atomic clocks, such as cesium atomic clocks, have seen significant advancements aimed at improving performance. Developments include single-ion clocks and optical lattice clocks, which use optical frequencies as reference standards. Recently, nuclear clocks, particularly those based on the nuclear isomer of thorium-229, have gained increasing interest. Unlike conventional atomic clocks based on electronic transitions, nuclear clocks utilize nuclear transitions as their reference frequency. Since nuclear transitions are less susceptible to external perturbations, they hold the potential for even higher precision. We are aiming to develop an ion-trap-based nuclear clock. So far, we have successfully trapped the ions necessary for this clock. The next step is laser cooling, as the Doppler effect causes the ions to shift the frequency of absorbed laser light according to their velocity, which requires cooling the ions to low temperatures to mitigate this effect. In this presentation, I will first explain the fundamental concept of the thorium-229 nuclear clock and ion trap, followed by our approach to laser cooling of triply charged thorium, which is essential for realizing a highly precise nuclear clock.
発表言語 日本語
発表者名 押金　こよみ
指導教員名 齊藤　英治　教授
発表題目（英語） Free energy-based machine learning using thermal equilibrium dynamics of physical systems
要旨（英語） In recent years, the free energy principle has been proposed as a framework to describe brain-based information processing; the brain learns by minimizing the information-theoretic free energy. On the other hand, in physical systems with many degrees of freedom, Helmholtz free energy minimization naturally occurs at thermal equilibrium. This leads us to realize that if we can reframe the objective function minimization problem in machine learning as a free energy minimization problem in a specific physical system, solutions can be obtained simply by measuring the thermal equilibrium state of the system.

In this study, we induced nonlinear magnetization dynamics in a magnetic NiFe thin film sample, which were employed as the physical response that is dual to the minimization problem. We will present details of this new machine learning methodology, experimental results, and examples of machine learning demonstrations.
発表言語 日本語
発表者名 香川　巧
指導教員名 高橋　陽太郎　准教授
発表題目（英語） In-plane Kerr effect in EuCd2Sb2
要旨（英語） Ordinary Hall effect requires out-of-plane magnetic field, but recently in-plane Hall effect induced by in-plane magnetic field has been reported. EuCd2Sb2 is one of the materials in which in-plane Hall effect is observed. This material is A-type antiferromagnet and has Weyl points near the Fermi level.

Magneto-optical Kerr effect is a change in a linear polarized light after reflection at the surface with Out-of-plane magnetic field or magnetization. This effect is connected to σ_xy(ω) as well as Hall effect σ_xy, so a lot of research has been done related to anomalous Hall effect, quantum anomalous Hall effect and so on. In this presentation, I will explain our experiment on in-plane Kerr effect in EuCd2Sb2 induced by in-plane magnetic field.
発表言語 日本語
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