応用物理学輪講 I
12月13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12月13日（金）16：50～18：50

Aグループ

座長
肥田　宏太郎
指導
教員名
中村　泰信　教授
発表者名 松田　優馬
指導教員名 川﨑　雅司　教授
発表題目（英語） Strain response of exciton-enhanced shift current
要旨（英語） A focus of the recent development in the electronic states in solids is their topological aspects and their influence on the physical properties. More explicitly, the Berry phase of the Bloch wavefunctions in the space of crystal momentum is found to determine the ferroelectricity.
Modern theory of polarization elucidated the mechanism of the anomalous photovoltaic effect in bulk crystals with broken spatial inversion symmetry which could not be described by classical theory. That’s the shift current, DC current generated as a result of second nonlinear optical response, in which Berry phase appears. I will talk about how to observe experimentally the exciton-enhanced shift current and its sensitive response to strain.
発表言語 日本語
発表者名 松本　滉永
指導教員名 木村　剛　教授
発表題目（英語） Electric-field-induced Toroidal Moment in Time-reversal-broken Antiferromagnets
要旨（英語） Recently, time-reversal-odd antiferromagnets have attracted attention for exhibiting ferromagnet-like behaviors (e.g., anomalous Hall effect and magneto-optical Kerr effect) despite the absence of net magnetization. In our study, we investigated a novel phenomenon in a time-reversal-odd antiferromagnet, that is, the diagonal electrotoroidic (ET) effect in which the application of an electric field E induces a magnetic toroidal moment T along E. While the off-diagonal response (T⊥E) of the ET effect is known to occur in ferromagnets, there has been no experimental observation of the diagonal effect (T || E).

In this presentation, we show our observation of electric-field-induced magnetic toroidal moment in a time-reversal-broken antiferromagnet, Co2SiO4. For this observation, we measured nonreciprocal directional dichroism, a representative phenomenon in ferrotoroidic systems, under applied electric fields. This technique allows us to visualize time-reversal antiferromagnetic domains.
発表言語 日本語
発表者名 三澤　遼
指導教員名 Max　Hirschberger　准教授
発表題目（英語） Loop-current order in solids
要旨（英語） In condensed matter physics, hidden order—characterized by an order parameter that eludes detection by conventional probes—has been of enduring interest. A prominent example is loop-current order, in which magnetic flux induces orbital currents or complex hopping. Since the complex hopping is odd under both spatial and temporal inversion, it corresponds to an ordering of "anapoles" or toroidal moments, which spontaneously breaks inversion and time-reversal symmetry.

Here, we briefly review loop-current order, covering the seminal work by Haldane on the honeycomb lattice and the manifestation in the pseudogap phase of cuprates. Subsequently, we discuss putative loop-current order in Kagome metals with 3Q charge density wave (CDW) order, the order parameter of which remains elusive. Introducing our novel approach to identifying the hidden order parameter, we present our experimental findings on versatile structural instabilities in a class of Kagome metals, including the discovery of a new type of 3Q CDW order.
発表言語 英語
発表者名 鈴木　大吾
指導教員名 石坂　香子　教授
発表題目（英語） Direct Observation of Ultra flat band in Van der Waals Kagome Matter Pd 3P2S8
要旨（英語） With the advanced investigations into low-dimensional systems, it has become essential to find materials having interesting lattices that can be exfoliated down to monolayer. One particular important structure is a kagome lattice with its potentially diverse and vibrant physics. Pd3P2S8 is a non-magnetic layered semiconductor (optical gap: ~2 eV) in which Pd atoms form a Kagome lattice, and the fabrication of single-layer flakes by tape peeling was reported in 2020. On the other hand, the bandwidth of the single layer has been calculated to be ~2 eV. In the band calculation of a single layer, a flat band with extremely narrow bandwidth (Ultra-Flat Band) is expected to appear isolated at the top of the valence band, and a strong modulation of the electronic structure by atomic layering is expected. In this study, we will directly observe the “Ultra flat band” by microscopic synchrotron radiation ARPES of single-layer flake samples, and also perform ARPES of multi-layer flake/bulk samples to investigate the difference in electronic structure from that of single-layer samples.
発表言語 日本語

Bグループ

座長
平﨑　雄太
指導
教員名
齊藤　英治　教授
発表者名 松田　仁
指導教員名 有田　亮太郎　教授
発表題目（英語） First-principles study of spin-orbit coupling-free responses in an exotic collinear antiferromagnet
要旨（英語） Altermagnets are collinear antiferromagnets that break time-reversal symmetry and exhibit spin split even without spin-orbit coupling (SOC). In contrast, collinear antiferromagnets that preserve time-reversal symmetry show spin degeneracy without SOC and possess a nonzero propagation vector. Some of these antiferromagnets exhibit spin degeneracy due to symmetries beyond PT symmetry. Through first-principles calculations, this study demonstrates that such collinear antiferromagnets with spin degeneracy can generate the Berry curvature and the Berry curvature dipole even without SOC.
発表言語 日本語
発表者名 山内　健聖
指導教員名 関　真一郎　准教授
発表題目（英語） Exploration of new time-reversal-symmetry broken antiferromagnet
要旨（英語） Recently, time-reversal-symmetry (TRS) broken antiferromagnet (AFM) is attracting much attention for its potential to enhance the performance of magnetic devices. In conventional magnetic memory devices such as MRAM, ferromagnet (FM) is utilized in information storage area and TRS-breaking in FM plays an important role in memorizing 0/1-bit information. However, FM has finite net magnetization and can lose their information due to their interference.
Until now, several TRS-broken AFMs were found, and it was indicated that they can show large response of anomalous Hall effect without net magnetization due to fictious magnetic field originated from Berry curvatures. Especially, collinear TRS-broken AFMs are sometimes referred to as “altermagnet” in recent years and many theoretical/experimental research are in progress. If we can substitute FM into such kind of AFM, which has fictitious magnetic field without net magnetization, magnetic memories will be able to avoid undesirable interference.
In this presentation, I will explain characteristic properties of TRS-broken AFM, their possible applications, latest material exploration, and our recent results of experimental searching for new material candidates.
発表言語 日本語
発表者名 山岡　良太
指導教員名 中島　多朗　准教授
発表題目（英語） Polarized and unpolarized neutron scattering study on the van der Waals magnet CrNb4Se8
要旨（英語） In recent years, van der Waals (vdW) magnetic materials have been actively studied in the field of solid-state physics. These materials allow for the design of physical property responses by combining atomic layers extracted through exfoliation. In particular, there has been growing interest in introducing spin degrees of freedom into these materials to explore new cross-correlation phenomena. For such research, the discovery of novel vdW magnetic materials is crucial.

In this study, we focused on CrNb₄Se₈, a vdW magnetic material containing magnetic chromium ions. Polarized and unpolarized neutron scattering experiments were conducted on a bulk single-crystal sample using the 5G PONTA spectrometer at JRR-3. We present the results of these measurements, including crystal structure analysis, magnetic structure analysis, and temperature dependence of magnetic correlation lengths, and discuss the dimensionality of the magnetic correlations.
発表言語 日本語
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