応用物理学輪講 I
6月16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6月16日(金)16:50~18:50

Aグループ

座長
吉田 昂永
指導
教員名
武田 俊太郎 准教授
座長
吉冨 成哉
指導
教員名
求 幸年 教授
発表者名 大野 亮汰
指導教員名 長谷川 達生 教授
発表題目(英語) Stepwise crystal structure optimization of polyacenes and elucidation of stability in layered herringbone structure.
要旨(英語) Charge transport of organic semiconductor strongly depends on molecular arrangement, so realization of crystal structure prediction and understanding the structural stability of crystal structure is important for developing high-performance materials. To solve these problems, we developed stepwise crystal structure optimization method where we separate intralayer packing and interlayer stacking based on high layered crystallinity in OSC materials and optimize them in order.

We first conduct research on reproducing and clarifying the origin of the known crystal structure for the purpose of accomplishing crystal structure prediction. In this research I apply this optimization method to polyacenes, a series of linearly condensed acenes. Polyacenes provide five stable compounds from naphthalene (ring number *n* = 2) to hexacene (*n* = 6), and form layered herringbone (HB) structure where neighboring molecules are arranged by *T*-shaped (face-to-edge) and parallel (edge-to-edge) contacts. Comparing the layered HB structure of polyacenes, changes of molecular arrangements with the increase of benzene rings are confirmed and there are four types of crystal structure in polyacene molecule. I succeeded in reproducing these four structures and clarifying the structural origin of these polymorphs by using stepwise optimization method. In this presentation I am going to show you detail of the method and calculation result.
発表言語 日本語
発表者名 大橋 悠生
指導教員名 福谷 克之 教授
発表題目(英語) Evaluation of hydrogen adsorption and absorption states of Bi2Se3 thin film surface: towards observation of the inverse Edelstein effect
要旨(英語) Spintronics research is being actively conducted worldwide. The generation and detection of spin currents are especially important technologies in spintronics. Electron spins injected on a spin-momentum locked surface, as in a topological surface state, acquire momentum in the direction perpendicular to the spin polarization direction, and thus a current flow on the surface, which is known as the inverse Edelstein effect [1]. We have developed a spin-polarized-hydrogen beam (SPH) [2] which is expected to reveal an inverse Edelstein effect at a surface. In this study, we aim to observe the spin-charge exchange from the SPH which is a completely new project. Before that, it is necessary to examine hydrogen adsorption and absorption states of Bi2Se3 which is a prototypical 3D topological insulator.
Bi2Se3 thin films were prepared on Si (111) by molecular beam epitaxy [3]. Bi2Se3 thin film was exposed to atomic hydrogen at 300 K and 77 K. I observed the surface crystal structure of Bi2Se3 after exposure to atomic hydrogen using Low Energy Electron Diffraction (LEED). It was found that atomic hydrogen dose to Bi2Se3 reduced its crystallinity. Then, Thermal desorption spectroscopy (TDS) was conducted to investigate the adsorption and absorption states of Bi2Se3. It was shown that desorption of not only H2 but also Se(hydride) and Bi(hydride) occurs and crystallinity was restored after TDS. Also, the process of desorption differed between exposure at 300 K and 77 K. In this presentation, I will discuss the origin of the adsorption and adsorption states of Bi2Se3, where hydrogen is intercalated between the Bi2Se3 quintuple layers in addition to surface adsorption.

[1] Ka Shen, et al., Phys. Rev. Lett. 112, 096601 (2014).
[2] Y. Nagaya, et al., J. Chem. Phys. 155, 194201 (2021).
[3] G. Zhang, et al., Appl. Phys. Lett. 95, 053114 (2009).
発表言語 日本語
発表者名 大村 昂輝
指導教員名 川﨑 雅司 教授
発表題目(英語) Topological Hall effect through proximity effect at hetero interface of DyFeO3/CaRuO3
要旨(英語) Topological Hall effect is an emergent magnetotransport phenomenon observed in magnetic metals with non-coplanar spin textures. Conducting electrons receive the Berry phase from the spin texture and feel an emergent field proportional to its scalar spin chirality. Various materials have been reported to exhibit this phenomenon, such as materials with skyrmion and spin-ice structure. However, all of these experiments have been performed on single crystals of magnetic metal. In this setup, it is difficult to modulate the magnetic and metallic properties independently, and advanced experiments to see detailed THE nature haven’t been feasible.

In my study, magnetic and metallic properties are separated into two layers by fabricating heterostructure of DyFeO3 and CaRuO3. This setup will allow advanced experiments by chemical substitutions to each layer. I will talk about the sample fabrication and topological Hall effect observed at the hetero interface.
発表言語 日本語

Bグループ

座長
吉永 享太
指導
教員名
木村 隆志 准教授
座長
梁 啓民
指導
教員名
古川 亮 准教授
発表者名 大村 哲士
指導教員名 森本 高裕 准教授
発表題目(英語) Exploration of ground states in spin-orbit coupled systems
要旨(英語) An orbital order is a phenomenon where the orbital degrees of freedom of electrons are aligned in solids. The orbital orders have not been fully investigated compared to magnetic orders where the spins of electrons are aligned, since it is difficult to measure orbital degrees of freedom directly. However, the orbital order plays a crucial role in some systems. For example, in the perovskite manganese oxides, which is a representative strongly correlated electron system, many tantalizing phenomena have been observed like colossal magnetoresistance (CMR) due to the orbital effect [1]. In this presentation, I will discuss ground states of the spin-orbit coupled system in LaMnO3 using a simple Monte Carlo method.
First, I will derive Kugel-Khomskii model in LaMnO3 where electrons split into localized and itinerant ones. Under crystal field effects, manganese ions host one electron in eg orbitals, which results in orbital degrees of freedom. In the strongly correlated limit, electrons can move nowhere, and an effective spin-orbit Hamiltonian can be derived. Due to the Hund coupling to the localized magnetic moments, the degeneracy of the energy of the virtual states is lifted, which makes spins and orbitals inequivalent.
Next, I will introduce Markov chain Monte Carlo method (MCMC) as a simple and powerful tool to explore classical ground states without a preferable ansatz. Unlike simple mean-field analyses, MCMC can provide probability distributions around ground states, corresponding to a given Hamiltonian. As an exercise of MCMC, I will confirm that the previous result [2] of the ground states of Kugel-Khomskii model in LaMnO3 holds true. If time allows, I would like to touch on my recent calculation about a spin-orbit coupled bilayer system.

[1] Y. Tokura, Rep. Prog. Phys. 69, 797 (2006).
[2] R. Shiina, T. Nishitani, and H. Shiba, J. Phys. Soc. Jpn. 66, 3159 (1997).
発表言語 英語
発表者名 門 恭平
指導教員名 関 真一郎 准教授
発表題目(英語) Emergent inductance in ferromagnets
要旨(英語) An Emergent Electric Field, which is an effective electric field due to a time-varying, non-collinear magnetic structure, has attracted a keen attention because of the potential for realizing inductor based on novel principle, called “Emergent Inductor”.
In addition to helical magnetic structure, which are mainly targeted in recent studies on emergent inductance[1][2], ferromagnetic domain walls, which are ubiquitously found in ferromagnets, also have the potential to generate inductive emergent electric fields.
Research on typical ferromagnetic materials, such as permalloy and cobalt, will be helpful to deepen our understanding of the physics of emergent inductors.
In this presentation, I will show some results of LLG simulations about emergent inductance in ferromagnetic domain walls and some experimental results about impedance measurement on ferromagnet CoFeB.

[1]T. Yokouchi, et al., Nature 586, 232-236(2020)
[2]A. Kitaori, et al., PNAS 118, 33(2021)
発表言語 日本語
発表者名 加藤 幹太
指導教員名 為ヶ井 強 准教授
発表題目(英語) Field-angle dependence of anomalous peak effect in (Ba,K)Fe2As2 with splayed and tilted columnar defects
要旨(英語) It is known that columnar defects introduced by heavy ion irradiation can enhance the critical current density of superconductors. The critical current density normally decreases monotonically with the applied magnetic field. However, a phenomenon called anomalous peak effect occurs for samples with spray columnar defects, where columnar defects cross at a certain angle. When a magnetic field parallel to the c-axis is applied, the critical current density increases with the magnetic field in a specific field range and shows a peak. A similar non-monotonic behavior of critical current density is also observed for samples with tilt columnar defects, which are inclined from the c-axis in one direction, when the magnetic field is aligned with the defects. This was reported in a previous study on NbSe2.

In this study, we aimed to elucidate the conditions and mechanism of the anomalous peak effect by irradiating 320 MeV Au ions on Ba0.6K0.4Fe2As2 and creating samples with spray columnar defects by adding columnar defects with various densities in the other symmetrical direction to tilt columnar defects. We measured magnetization curves by changing the angle of applied magnetic field and investigated the possibility and behavior change of mixing anomalous peaks from tilt and spray columnar defects.
発表言語 日本語