応用物理学輪講 I
5月20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
2022年5月20日（金）　16：50～18：50（初回ガイダンスのため、16：45にＡグループのURLにアクセスしてください。）

Aグループ

座長
藤原　孝輔
指導
教員名
森本　高裕　准教授
座長
藤原　心
指導
教員名
芦原　聡　教授
発表者名 赤塚　駿
指導教員名 ﾏｯｸｽ　ﾋﾙｼｭﾍﾞﾙｶﾞｰ　准教授
発表題目（英語） Unusually high mobility and complex spin structure in van-der-Waals magnet DyTe3
要旨（英語） In recent condensed matter physics, "magnetism in two-dimensional systems such as transition metal dichalcogenides" and "non-coplanar magnetic structures such as magnetic skyrmions" have attracted a great deal of attention. Our research aimed to develop a new field that combines these two characteristics, "non-coplanar magnetic structure in two-dimensional materials", and focused on RTe3 (R = rare earth) as a candidate material.
RTe3 is a van der Waals substance that can be regarded as a pseudo-two-dimensional system, and is characterized by the reconstruction of the Fermi surface and high mobility accompanying the formation of charge density waves. In particular, previous studies have reported a magnetization curve suggesting that DyTe3 may have a non-coplanar magnetic structure.
In this study, we synthesized a single crystal DyTe3 and investigated its magnetic and transport properties. Magnetization measurements confirmed that it had a large number of magnetic phases, and the results of neutron scattering using powder samples suggested that at least non-colinear spin structures were formed. In addition, high mobility exceeding 180,000 cm2 / Vs and quantum oscillation were observed in the low temperature region as transport characteristics. On the day, I will discuss the origin of high mobility and the relationship between transport characteristics and magnetism.
発表言語 日本語
発表者名 陳　子彦
指導教員名 齊藤　英治　教授
発表題目（英語） Electronic ferroelectricity in RFe2O4 (R=Y, Lu, Yb...)
要旨（英語） Ferroelectric materials form the basis of electronic technology and are widely used in modern electronic devices. The ferroelectric phenomenon is typically caused by electric polarization resulting from the spontaneous displacement of polar ions. In this talk, I will introduce a novel type of ferroelectric material RFe2O4 (R = Y, Lu, Yb etc.), where the spontaneous polarization originates from the polar ordering of electrons rather than ionic atoms. I also talk about a recent report on the second harmonic generation (SHG), from which the point group and the charge order structure of YbFe2O4 were uniquely determined.
発表言語 英語
発表者名 万　秋明
指導教員名 芦原　聡　教授
発表題目（英語） Surface-enhanced infrared absorption spectroscopy using resonant plasmonic nanostructures for monitoring electrochemical processes.
要旨（英語） We are developing a new platform for sensitive monitoring of electrochemical processes by utilizing surface-enhanced infrared absorptionspectroscopy with resonant plasmonic nanostructures.
In this talk, I will introduce the concept of our study and present our recent progresses.
発表言語 英語

Bグループ

座長
古谷　登
指導
教員名
木村　隆志　准教授
座長
松澤　創一郎
指導
教員名
為ヶ井　強　准教授
発表者名 荒木　那巨
指導教員名 関　真一郎　准教授
発表題目（英語） Microwave spectroscopy in polar magnetic insulator VOSe2O5
要旨（英語） Inversion symmetry breaking in crystal structures can lead to unusual physical properties and nontrivial responses to external fields. In magnetic materials, inversion symmetry breaking allows for the existence of Dzyaloshinskii-Moriya (DM) interactions, which can lead to a variety of magnetic spin textures. In addition, a large photovoltaic effect has recently been observed in materials with broken space-inversion symmetry, depending on a quantum mechanical mechanism called the shift current, simply by irradiating visible light on the bulk crystals. From the above viewpoints, the development of magnetic materials with broken inversion symmetry is very valuable for applications.
In this presentation, we describe experimental observations of the microwave response of VOSe2O5, a magnetic material with broken space-inversion symmetry, which has been shown to exhibit helical magnetism under zero magnetic field due to the presence of DM interactions and an unusual magnetic structure called a Ne’el-type magnetic skyrmion at a certain condition[1,2].
In this research, we investigate the microwave response of such magnetic structures in detail. The presentation will begin with a general discussion of hellical magnetism, the magnetic structure in VOSe2O5, the setup of the present experiment, and finally the experimental results and future prospects.
[1] T. Kurumaji et al,. Phys. Rev. Lett. 119, 237201 (2017)
[2] T. Kurumaji et al,. J. Phys. Soc. Jpn. 90, 024705 (2021)
発表言語 日本語
発表者名 ＷＵ　Wenxi
指導教員名 為ヶ井　強　准教授
発表題目（英語） Magnetic-field trapping in (Ba,Na)Fe2As2 bulk
要旨（英語） Superconductors with a large critical current density (Jc) can trap a high magnetic field when large single-grain crystals are prepared or their powders are pressed into bulk. This technique has been applied to YBa2Cu3O7, MgB2, and iron-based superconductors. However, the maximum trapped field of YBa2Cu3O7 bulk is limited by its material strength due to its single-grain like nature and that of MgB2 bulk is limited by its low Hc2 and it is easily affected by flux jumps. Given the large Hc2, Ba122 iron-based superconductor polycrystalline bulk with large dimensions have a potential to trap a large field.
In the present study, we have prepared two cylindrical bulks with polycrystalline Ba0.6Na0.4Fe2As2 superconductor, bulk #1 with a diameter of 2.6 mm and bulk #2 with a diameter of 4.8 mm. The thicknesses of these two bulks are each close to their diameters. Polycrystalline powder was synthesized by using mechanochemical reaction and proved to be of high quality. The bulk samples are processed by a hot isostatic pressing (HIP) at ~1.75 kbar of the prepared superconductor powder inside a silver/copper double-sheathed tube. A relatively sharp transition (with a width about 2 K) of magnetization around Tc indicates that the composition of the superconducting bulks has not changed after the heat treatment and the powder in both bulks has been successfully pressed in the sheath. On the other hand, the highest Jc value in the bulks is only 80 kA/cm2 (4.2 K, self-field) in bulk #1, which is lower than expected. And in bulk #2, the Jc value is only around 40 kA/cm2. This suggests that there are cracks inside the bulks. The trapped field is calculated to be 0.612 T in bulk #1 and 0.661 T in bulk #2. Improper sealing method may be the reason for this low Jc. It will lead to a lower pressure on the sample during the HIP process and this may be the reason for the low Jc and trapped field. Thus, improving the pressing and sealing methods (e.g., using high pressure furnace to improve the pressure and avoid difficult sealing operations) is what we plan to do in the future.
発表言語 英語
発表者名 祖　宇航
指導教員名 為ヶ井　強　准教授
発表題目（英語） Imaging of nematic domains in a topological superconductor SrxBi2Se3
要旨（英語） Recently, topological insulators (TIs) and topological superconductors (TSCs) have become star materials, drawing intense research interest because of their novel physical properties and potential applications in electronic devices. Bi2Se3, the most famous topological insulator, becomes topological superconductors by doping Cu or Sr. These materials attract much interest because of the nematic state showing two-fold symmetry when magnetic field is applied parallel to ab-plane. In this study, we introduce SrxBi2Se3 and its in-plane magnetic-field-angle dependence of resistivity measurements by using high-quality single crystals. The results show two-fold symmetry and indicates the existence of nematic domains. What’s more, the fitting to the in-plane magnetic-field-angle dependence of magnetoresistance also indicates that exotic current path may appear. Furthermore, possible methods of synthesizing higher-quality SrxBi2Se3 single crystals and possible experiments of direct visualization of nematic domains will be discussed.
発表言語 英語
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