応用物理学輪講 I
5月19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
2023年5月19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
陳　子彦
指導
教員名
齊藤　英治　教授
座長
森石　奎吾
指導
教員名
高橋　陽太郎　准教授
発表者名 松永　響
指導教員名 有田　亮太郎　教授
発表題目（英語） Development of a first-principles method for critical magnetic field(Hc) and critical current (Ic) of superconductors
要旨（英語） The first-principles calculation of superconductors is one of the challenges in condensed matter physics. In recent years, it has become possible to calculate the transition temperature(Tc) of conventional superconductors with low transition temperatures using the intermediate representation (IR) of the Green's function and the sparse sampling method. The next challenge is to calculate the critical magnetic field(Hc) and critical current(Ic). These can be obtained by first-principles calculations of coherence length(ξ) and London penetration depth(λ), and particularly, the calculation of coherence length(ξ) is enabled by the calculation of the transition temperature of the FFLO state. In this seminar, we will explain why first-principles calculations were difficult for superconductors with low transition temperatures and how this difficulty was overcome. We will also introduce the calculation methods for the critical magnetic field(Hc) and critical current(Ic).
発表言語 日本語
発表者名 陈　杨菘
指導教員名 為ヶ井　強　准教授
発表題目（英語） Elucidation of critical current of 1144-type iron-based superconductors
要旨（英語） Among iron-based superconductors, there are iron-based superconductors of type "122", including BaxK1−x Fe2As2 and SrxK1−x Fe2As2. They have a larger critical current Jc, a higher critical magnetic field Hc2, smaller anisotropy, and stronger intergranular connectivity. In 2016, a new type of iron-based superconductor, the 1144-type iron-based superconductor (AeAFeAs-1144) , was discovered, which is a variation from type "122" . Compared with 122-type iron-based superconductors, Ae and A do not occupy equivalent positions in crystallography due to the large difference in atomic radii. Typically, the critical current Jc of a superconductor decreases as the temperature increases. However, for CaKFe4As4 at high magnetic fields, the critical current Jc presents a very different temperature dependence. At the same time, the increase in the magnetic field is that the Jc curve of CaKFe4As4 will have a fishtail effect. This means that the application prospects of this material under high fields are very broad. According to different defect conditions, its magnetic properties and critical current also have completely different performances.
発表言語 英語
発表者名 于　澄
指導教員名 為ヶ井　強　准教授
発表題目（英語） Trapping Magnetic Field in Stacked Coated Conductors
要旨（英語） We fabricated a compact (12x13x19.4 mm3) trapped field magnet by stacking 300 pieces of EuBa2Cu3O7 coated conductors with BaHfO3 as artificial pinning centers. Each piece was cut by laser to minimize the cutting-induced damage. It was magnetized by field-cooling method using the 18 T superconducting magnet. As a result, the maximum filed of 15.27 T was trapped at 7 K, which is lower than that achieved in the previous study. Several causes of the inferior performance of the new stacked magnet are analyzed.
発表言語 英語
発表者名 曾　可嘉
指導教員名 芦原　聡　教授
発表題目（英語） Development of mid-Infrared ultrafast laser using Cr:ZnS oscillator and fluoride fiber
要旨（英語） Vibrational spectroscopy is an important experimental tool to understand the physical structure and dynamical properties of molecules. If we excite molecules with light and then analyze the spectrum of the light, we can get detailed information of those molecules. Since most molecules have resonant frequencies lying in the mid-infrared (MIR) region, which is also called the “molecular fingerprint region”, suitable light source in MIR region is required.

However, producing an MIR ultrafast laser directly is challenging due to a lack of a suitable gain medium in that region. In general, nonlinear wavelength conversion is required to shift the laser spectrum to longer wavelength in order to reach the MIR region.

My research purpose is to develop a new light source in the MIR region with broad spectrum, excellent spatial coherence, and high output power based on Cr:ZnS oscillator and soliton self frequency shift(SSFS)effect in optical fiber. Especially aiming at the applications for spectroscopy in 3~5μm wavelength region.
発表言語 英語

Bグループ

座長
万　秋明
指導
教員名
芦原　聡　教授
座長
矢島　康平
指導
教員名
渡辺　悠樹　准教授
発表者名 青木　俊太
指導教員名 岩佐　義宏　教授
発表題目（英語） Observation of the second harmonic generation in van der Waals antiferromagnet CuCrP2S6
要旨（英語） Two-dimensional magnet is attracting much attention as a new material platform for the search of novel magnetic properties. It shows the magnetic order even in few-layer samples [1,2], which can be thickness-dependent or modulated by applying the external field. Especially, in two-dimensional antiferromagnets, a variety of complex magnetic structures can be realized, thus offering unique magnetic properties and functionalities. However, since antiferromagnetic materials do not have net magnetization, it is generally difficult to observe the magnetic phase transition using magneto-optical Kerr effect or magnetic circular dichroism, which are frequently used for studying two-dimensional ferromagnets. Instead, second harmonic generation can be a good tool for studying the magnetism and resultant magnetic symmetries of two-dimensional antiferromagnet [3-6].

In this presentation, I will talk about the second harmonic generation in exfoliated flake samples of the van der Waals antiferromagnet CuCrP2S6. In the previous studies [7], it is reported that CuCrP2S6 shows a structural phase transition around 150 K from centrosymmetric to non-centrosymmetric crystal structure and an antiferromagnetic phase transition around 32 K. In the present study, we have successfully observed the second harmonic generation reflecting these structural and antiferromagnetic phase transitions. In my talk, the characteristic behaviors of the SHG signal and their origins will be also discussed.

[1] C. Gong *et al., Nature*, *546* 265(2017)
[2] B*. *Huang *et al., Nature*, *546* 270 (2017)
[3] Z. Sun *et al*., *Nature* *572*, 497 (2019)
[4] H. Chu *et al.,* *Phys. Rev. Lett.,* *124*, 027601 (2020)
[5] Z. Ni* et al., Nat. **Nanotech.*, *16* 782 (2021)
[6] K. Lee *et al.,* *Nano Lett. **21*, 3511 (2021)
[7] C. C. B. Park *et al.* *Adv. Electron. Mater.* 2101072 (2022)
発表言語 日本語
発表者名 相原　孝広
指導教員名 高橋　陽太郎　准教授
発表題目（英語） Bulk photovoltaic effect induced by electromagnon excitations in multiferroics RMn2O5 (R = Y)
要旨（英語） Bulk photovoltaic effect (BPVE) is a 2nd nonlinear optical process which converts light into electricity. One microscopic mechanism that explains BPVE is the shift current mechanism. Shift current is the photocurrent which arises when the real-space center of charge shifts by light excitation and has attracted much recent attention in terms of the quantum-mechanical geometric phase of electronic states. This shift current had been thought to arise with interband transition, but it is now known that they are also caused by elementary excitations, such as soft phonon in terahertz region [1]. In this presentation, we focus on the shift current induced by electromagnon excitations, which are specific to multiferroics in the terahertz region. It was theoretically proposed [2][3] and successfully observed for the first time in our lab.
In this session, after explaining the BPVE and the shift current mechanism, the basic physical properties of the target material multiferroics RMn2O5 (R = Y), measurement methods, experimental results, and the microscopic origins of the BPVE will be presented.

[1] Y. Okamura, et al. PNAS 119, e2122313119 (2022).
[2] T. Morimoto et al., Phys. Rev. B 100, 235138 (2019).
[3] T. Morimoto et al., Phys. Rev. B 104, 075139 (2021).
発表言語 日本語
発表者名 赤塚　俊輔
指導教員名 石坂　香子　教授
発表題目（英語） Breaking of spatial inversion symmetry in 180-degree-twisted bilayer ReSe2
要旨（英語） The development of mechanical exfoliation and dry-transfer techniques has made it possible to stack two-dimensional flakes dynamically and fabricate new materials that cannot be synthesized through thermodynamic processes. In such composite flakes, changes in the symmetry of the crystal structures can lead to emergent physical properties that would not appear in each component flake alone.

Here, we fabricated a 180-degree-twisted bilayer (180-BL) ReSe2 with a spatial-inversion-symmetry broken crystal structure by stacking monolayer ReSe2 flakes with a centrosymmetric 1T-distorted crystal structure. By angle-resolved photoemission spectroscopy and second harmonic generation, we observed the emergent band dispersions and the artificially induced spatial-inversion-symmetry breaking in the 180-BL ReSe2. Our result fully demonstrates the potential of creating new materials that can exhibit spintronic functions and Berry-curvature-related physical phenomena by controlling the presence or absence of spatial inversion symmetry.
発表言語 日本語
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