応用物理学輪講 I
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古澤 千晶
賀川 史敬 准教授
古山 昂樹
志村 努 教授
発表者名 村田 啓人
指導教員名 長谷川 達生 教授
発表題目(英語) Influence of layer structure in extremely sharp switching organic TFT
要旨(英語)  Among organic thin-film transistors (OTFTs), which are basic elements of organic electronics, bottom-contact-type OTFTs (BC-OTFTs) are suitable for practical use because electrodes can be fabricated without any damage to organic semiconductors(OSCs) and enable direct carrier injection from an electrode to transfer channel. On the other hand, device performance of BC-OTFTs is known to be lower than that of other contact-type OTFTs and this trend is considered to be attributed to carrier behavior at the ternary interface of electrode/semiconductor/insulator, which is unique to BC type. However, this mechanism has complex factors and is not fully understood.
 In recent years, due to the development of the solution-based process of fabrication of single-crystalline OSC films on insulator with the low surface energy, BC-OTFTs with stable operation, high mobility, and shape switching was realized and it is now possible to obtain an ideal semiconductor/insulator interface. In this study, we focused on semiconductor layer structure in these nearly ideal systems for further investigation and found that device performance drastically improves depending on the number of layers. Based on the correlation between device performance and surface potential distribution measured by KFM, I will discuss its origin and carrier behavior at the ternary interface.
発表言語 日本語
発表者名 森 春仁
指導教員名 賀川 史敬 准教授
発表題目(英語) Real space observation of non-equilibrium steady states in (DMe-DCNQI-d8)2Cu
要旨(英語)  It has been known for a long time that metastable states can be obtained by quenching materials. Recently, it has been reported that metastable states can be obtained not only in atomic and molecular systems but also in electronic systems by applying quenching.
 In (DMe-DCNQI-d8)2Cu, which exhibits a first-order metal-insulator phase transition, it has been reported that a steady state with a resistivity intermediate between that of metal and insulator can be obtained by cooling with an applied current. In other words, unlike conventional charge glasses, DCNQI exhibits a non-equilibrium steady state with two components: a dissipative structure and a metastable state.
 In this study, I aim to investigate the formation mechanism of the non-equilibrium steady state under current in detail, and I report the results of real-space observation of the non-equilibrium steady state of (DMe-DCNQI-d8)2Cu using a Raman microscope.
発表言語 日本語
発表者名 安波 貴広
指導教員名 川﨑 雅司 教授
発表題目(英語) Fabrication of BiI3 film by MBE technique and its optical property
要旨(英語)  BiI3 is a layered semiconductor and studied for its exciton property. BiI3 exciton property is studied because the exciton binding energy and the value of the absorption coefficient are large. Recently BiI3 is also focused as a material for solar cells because the bandgap is around 2 eV. However, there is no report on the fabrication of high-quality film.
 In this seminar, I talk about how to synthesize high-quality BiI3 film and the film’s optical property. I fabricated BiI3 film by MBE method and I found that in order to synthesize high-quality BiI3 film, deposit very thin buffer layer at low temperature before main growth is important. Optical measurement indicates that our film crystalline is comparable with bulk, because the value of absorption coefficient and the outline of photoluminescence spectra resemble bulk single crystal.
発表言語 日本語
発表者名 佐藤 秀樹
指導教員名 志村 努 教授
発表題目(英語) Modulation of light waves by the dielectric meta-surface
要旨(英語)  The rod-shaped structure of a metal or dielectric with a length of about 100 nm, so-called nanorods, functions as an electric dipole when light is irradiated, and the dipole that oscillates at the frequency of light is induced. Dipole radiation occurs from vibrating polarization, and it interferes with the incident wave and becomes an output wave. Since the phase difference between the vibration polarization and the incident light wave changes depending on the difference between the resonance frequency of the electric dipole and the frequency of the incident light wave, the phase of the emitted wave can be controlled by changing the size of the nanorod. The meta-surface is an arrangement of such nanorods in two dimensions. By spatially arranged nanorods with different resonance frequencies, it is possible to control the wavefront. Optical elements such as meta-lenses and meta-holograms have already been reported. Metal nanorods generate greater polarization due to plasmons, but also have large absorption loss. Dielectric nanorods, on the other hand, have low absorption loss and are advantageous in terms of actual device applications. In this presentation, we describe the control of light waves by dielectric meta-surfaces and their applications.
発表言語 日本語


福田 光
十倉 好紀 卓越教授
藤本 健
齊藤 英治 教授
発表者名 矢田 季寛
指導教員名 沙川 貴大 教授
発表題目(英語) Quantum fluctuation theorem under continuous measurement and feedback
要旨(英語)  In the last few decades, the framework of thermodynamics has been applied to small systems in which thermal or quantum fluctuation plays a crucial role. A key equation that quantifies a universal behavior of such systems is the fluctuation theorem (FT). The FT characterizes the behavior of entropy production in the nonlinear nonequilibrium region and also implies the second law of thermodynamics (SL).
 In the field of information thermodynamics, it has been pointed out that measurement and feedback alter the thermodynamic laws from their foundations. For instance, the FT and SL in classical systems have been generalized under various feedback control setups. However, the FT has not yet been studied in quantum systems under continuous measurement and feedback, despite the theoretical and experimental significance of the situation.
 In this presentation, I will talk about the generalized fluctuation theorem under continuous quantum measurement and feedback, which we derived analytically. The essence of the derivation is to newly introduce the operationally meaningful information, which we call quantum-classical (QC) transfer entropy. QC transfer entropy can be interpreted as the quantum counterpart of transfer entropy, which is the commonly used measure of information transfer in the classical time series analysis. We will also show the numerical demonstration and suggest an experiment-numerics hybrid verification method of the generalized FT.
発表言語 日本語
発表者名 山本 孝
指導教員名 岩佐 義宏 教授
発表題目(英語) Bulk photovoltaic effect in MoS_2 /Black phosphorus hetero interface
要旨(英語)  Van der Waals interfaces have attracted much attention as attractive material platforms because of the potential to realize the novel properties and functionalities by selecting combination of materials and twisting relative angle freely. Recently our group have reported that in-plane polarization and bulk photovoltaic effect can emerge in the symmetry-engineered interface of WSe_2 with three-fold rotational symmetry and Black Phosphorus (BP) with two-fold rotational symmetry [1]. In this study, bulk photovoltaic effect was observed in the symmetry-engineered interface of MoS_2 and BP which is similar interface with previous one and the observed spontaneous photocurrent showed the anisotropic behavior reflecting in-plane polar symmetry. In addition, we found that bulk photovoltaic effect in the interfaces can be originated from quantum-mechanical shift current model by comparing experimental results with theoretical calculation. The present results indicate that our method of symmetry engineering is effective and applicable to van der Waals interfaces of other crystal combinations.

[1] T. Akamatasu, T. Ideue /et al/., Science *372*, 68 (2021).
発表言語 日本語
発表者名 山本 崇人
指導教員名 石坂 香子 教授
発表題目(英語) Study of electronic states in two-dimensional van der Waals layered materials and their superstructures by angle resolved photoemission
要旨(英語)  In recent years, there has been extensive research to explore the novel properties of two-dimensional van der Waals materials, which are only a few atoms thick, such as graphene and transition metal dichalcogenides (TMD).Their superstructures also exhibit novel properties like magic angle graphene, which exhibits superconductivity at certain angles. Generally, it is difficult to determine their electronic structure by calculation due to the complexity of their periodic structure. However, the electronic structures can be observed experimentally by angle-resolved photoemission spectroscopy (ARPES).
 In my presentation, I will introduce how to fabricate superstructures of some TMD for ARPES measurement, its result, and future prospect.
発表言語 日本語