応用物理学輪講 I
6月18日
[注意事項]
発表の10日前までに宛てに「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
2021年6月18日(金)16:50〜

Aグループ

座長
董 禹
指導
教員名
岩佐 義宏 教授
座長
刘 彦慷
指導
教員名
渡辺 悠樹 准教授
発表者名 武田 和大
指導教員名 賀川 史敬 准教授
発表題目(英語) Real space observation of phase transition dynamics in transition metal dichalcogenides
要旨(英語) Transition metal dichalcogenides (TMDs) have attracted attention owing to their rich physics and potential applications using electronic phase control. The phase evolution of TMDs in real space can be revealed by measuring optical phonons with high spatial resolution using scanning Raman microscopy. However, to observe the phase transition in one of the target materials, MoTe2, it is necessary to investigate wavenumbers below the lower limit of the detectable range with the optical systems used so far.
In the present study, we improve our optical system to extend the range of measurable wavenumbers. In the presentation, I will show the experimental results of IrTe2 measured with the setup so far and the optical system which is currently being improved.
発表言語 日本語
発表者名 高木 寛貴
指導教員名 関 真一郎 准教授
発表題目(英語) Antiferromagnetic materials with broken time-reversal symmetry
要旨(英語) Recently, the concept of spintronics, i.e. the technology that utilizes not only charge but also spin degree of freedom of electrons, has attracted attention as the key to enable the innovative devices with rich functionality.
 So far, the spintronics has mainly focused on ferromagnets, where their magnetization and associated time-reversal symmetry breaking allow us to retain, read and write magnetic information. On the other hand, the recent discovery of antiferromagnets with broken time-reversal symmetry suggests that the latter systems can be another platform for the next generation of spintronics.
 A typical example is Mn3Sn with non-collinear antiferromagnetic order which breaks time-reversal symmetry[1]. Despite its antiferromagnetic character, this compound shows giant anomalous Hall effect[1] and anomalous Nernst effect[2], which have previously been reported only in ferromagnetic materials with macroscopic magnetization. Mn3Sn has topological Weyl nodes in its electronic band structure due to time-reversal symmetry breaking [3], and the associated fictitious magnetic field generated via the quantum Berry curvature plays a role equivalent to magnetization. Such antiferromagnets with broken time-reversal symmetry are expected to have a similar function to ferromagnets due to their fictitious magnetic field, but also with potential advantages specific to antiferromagnets, such as the absence of a magnetization-derived stray field. However, there are still only a few reported examples of time-reversal symmetry broken antiferromagnets, and in particular, the one with the collinear antiferromagnetic order has not been established yet. [4,5]. Therefore, the further search of such materials systems is highly demanded.
 In this presentation, I will discuss the current status of our research on such time-reversal symmetry broken antiferromagnets.
[1] S. Nakatsuji et al., Nature 527, 212 (2015).
[2] M. Ikhlas et al., Nature Phys. 13, 1085 (2017).
[3] K. Kuroda et al., Nature Mat. 19, 1090 (2017).
[4] N. J. Ghimire et al., Nature Comm. 9, 3280 (2018).
[5] G. Tenasini et al., Phys. Rev. Lett. 2, 023051 (2020).
発表言語 日本語
発表者名 中津 裕貴
指導教員名 福谷 克之 教授
発表題目(英語) Development of Spin-Polarized Atomic Hydrogen source
要旨(英語) The hydrogen atom consists of an electron and a proton, each of which has a spin 1/2. The hydrogen atom exists in spin singlet and triplet states under the zero magnetic field, but the degeneracy can be resolved with a magnetic field. By using a hexapole magnet, we can select the particular spin states of the hydrogen atom. The purpose of our study is to develop a Spin-Polarized Atomic Hydrogen source (SPH) and then we can use SPH to understand the surface magnetic structure through comparing the spin polarization before and after SPH scattering. Furthermore, SPH will reveal the mechanism how hydrogen molecules are formed on surfaces and the interaction between the nuclear spin of hydrogen atoms and surfaces. In this presentation, I will talk about how to generate and detect SPH and our recent study about the effect of Stern-Gerlach magnet on SPH, and future plans for the development of SPH.
発表言語 日本語

Bグループ

座長
任 統
指導
教員名
為ヶ井 強 准教授
座長
WOLSKI Samuel Piotr
指導
教員名
中村 泰信 教授
発表者名 高原 規行
指導教員名 川﨑 雅司 教授
発表題目(英語) Two-dimensional electron transport in magnetic oxide EuTiO3
要旨(英語) EuTiO3 (ETO) is a magnetic semiconductor where 7mu_B magnetic moment of Eu2+ shows antiferromagnetic ordering at T=5.5K. EuTiO3 shows metallic behavior by substituting Eu with donor impurity, and its magnet transport attracts much interest (e.g. anomalous Hall effect which is nonproportional to magnetization [1]). GdTiO3 (GTO) is a ferrimagnetic Mott insulator where Gd3+ has same 7mu_B magnetic moment as Eu2+. GTO/ETO interface is a polar-discontinuity interface and electron doping to ETO layer can be expected as reported in the other perovskite oxide heterostructure like LaAlO3/SrTiO3 or LaTiO3/SrTiO3. In this presentation, we report the physical properties of GTO/ETO heterostructures which were grown on LSAT (001) substrates by gas-source molecular beam epitaxy. We found that conductive electrons are induced at ETO layer with distribution thickness around 2nm. We introduce mainly the transport property and its ETO thickness dependence and we show the recent progress in this research.
[1] K. S. Takahashi *et al*. Sci. Adv. *4* (2018)
発表言語 日本語
発表者名 二階堂 圭
指導教員名 長谷川 達生 教授
発表題目(英語) Control of order/disorder phases in layered organic semiconductors
要旨(英語) Layered crystallinity of rod-like organic semiconductor (OSC) molecules is important for organic field-effect transistors (OFETs) because it allows OSC molecules to form high-quality carrier transport layer in self-organized manner. In this work, we focus on PE-BTBT-Cn, which is a recently-developed rod-like OSC molecule whose π-electron core is substituted asymmetrically by alkyl chain and phenylethynyl group. Since PE-BTBT-Cn exhibits various layered crystal phases depending on its alkyl chain length, we investigated this material as a model system of the emergence and stability of various layered crystal phases.
 According to the single crystal structure analysis, PE-BTBT-Cn exhibits unique disorder layered packing structure where the long axis of molecules is randomly oriented, when alkyl chain length is n = 6. However, we found that an introduction of a small amount of longer-alkylated molecules (n = 8, 10, 12) into the molecule of n = 6 suppresses the disorder, and the mixtures exhibit higher-order layered crystal phase. Based on the detailed thermal analyses on the mixtures, I will discuss the phase diagram of binary system and the thermodynamic stability of order/disorder layered crystal phases. I also demonstrate the impact of change in layered crystal structure on OFET performances.
発表言語 英語
発表者名 津坂 裕己
指導教員名 芦原 聡 教授
発表題目(英語) Vibrational control of chemical reaction with shaped mid-infrared pulses
要旨(英語) The mid-infrared (mid-IR) range of the spectrum corresponds to energies associated with molecular vibrations. Mid-IR ultrashort laser technologies have enabled multi-quantum vibrational excitation (or vibrational ladder climbing), and have opened a way to mode-selective control of chemical reactions. Deposition of sufficient energy into molecular vibrations participating in the reaction coordinate via IR laser excitation can promote a specific reaction while leaving the surrounding molecules undisturbed [1].
 In such vibrational control of chemical reactions, the waveform of the mid-IR pulsed field has an important role in efficiently exciting molecular vibrations into higher lying states. In this study, we numerically investigate the optimal waveform of the mid-IR pulse for vibrational ladder climbing based on Liouville von-Neumann equation. In this presentation, we will discuss the simulation results with our future plans to experimentally demonstrate vibrational ladder climbing with shaped mid-IR pulses.
[1] K. Heyne and O. Kuuhn, J. Am. Chem. Soc. 141, 11730 (2019).
発表言語 日本語