座長：三橋 洋亮、宮崎 優
|氏名： 青野 快
指導教員名： 石坂 香子 教授
発表題目（英語）： ARPES measurements and *ab*-initio calculations of a planar version of Heusler *ABC* (*A*=Eu/Gd) compounds for investigating more novel topological materials
要旨（英語）： Half-Heusler* ABC* materials have been attracting great attentions because of their high thermoelectric properties, and the potential of topological insulators. In addition, by substituting A-site ion for rare-earth one (*A*=Eu/Gd), their structures can convert to planar version of Heusler *ABC* (ZrBeSi-type) structures which have magnetism. In these compounds, more novel topological materials have been suggested both theoretically and experimentally, and the representative examples are *T*-broken Weyl Semimetal (WSM) and non-Dzyaloshinskii-Moriya (DM) hosting skymion lattice (SkL).
In this presentation, I will introduce the preceding research of *T*-broken WSM and non-DM hosting SkL materials in those compounds, explaining the great contributions of angle-resolved photoemission spectroscopy (ARPES) and *ab*-initio calculation to those experiments. In addition, we synthesized new Eu-based materials which have a planar version of Heusler *ABC*structure, and conducted ARPES measurements and *ab*-initio calculation of the materials, so I will also discuss the results and their properties as powerful candidates of more novel topological materials.
|氏名： 岩野 亜希人
指導教員名： 山地 洋平 特任准教授
発表題目（英語）： Exhaustive search for new high temperature superconductors in transition metal compounds by high precision numerical simulations
要旨（英語）：It has been known that the transition metal compounds, which are typical strongly correlated electron system, exhibit abundant physical properties due to the interaction of not only among charge degrees of freedom but also spin, orbital, and crystal lattice degrees of freedom. Copper oxide superconductors and iron-based superconductors are known as substances that show high-temperature (high-Tc) superconductivity, and both are transition metal compounds. However, at present, no established high-Tc superconductors other than compounds containing copper and iron have been found. In addition, there is no research that investigates the possibility of superconductivity in multi-orbital systems such as that found in iron-based superconductors in accurate and comprehensive way.
In this study, we aim to discover new high-Tc superconductors by using many-variable variational Monte Carlo method, which is known as a high-precision numerical calculation method, to examine the emergence of the high-Tc superconductivity in the wide variety of the crystal structure and elemental composition. In this presentation, the basics of the variational Monte Carlo method, the plan of the research, and the current progress, will be introduced.
|氏名： 新井 滉
指導教員名： 芦原 聡 教授
発表題目（英語）： Tunneling Current Induced by Ultrashort Optical Pulses
要旨（英語）： When a strong electric field more than 1 V/nm is applied to a material, an extremely nonlinear response appears. Since these phenomena are explained by field-driven electron, it is important to measure optical field precisely. Carrier envelope phase (CEP) measurement is necessary to get complete waveform of optical field. For this reason, the purpose of our study is to develop a simple and reliable CEP detector.
In our study, we focus on nano-metal structure. In strong-field regime, electron emission rate from metal approximately follows Fowler-Nordheim form of the instantaneous field. Therefore, emitted electrons shows field sensitivity and CEP dependence. Additionally, plasmonic enhancement makes positive contribution to the measurement.
In my talk, I will present a possible nano device design and show experimental methods for field sensitive measurement with some numerical calculation results of the optical field-driven current.
|氏名： 岩村 顕也
指導教員名： 中村 泰信 教授
発表題目（英語）： Electro-mechano-optical transducers with a metasurface mirror.
要旨（英語）： Techniques that can up-convert radio-frequency signals to optical signals in quantum limit can be of great importance for various quantum technologies such as quantum sensing and quantum communication, as well as for classical application such as medical imaging and astronomical observation.
One of the signal up-conversion techniques attracting attention is electro-mechano-optical (EMO) transducers. The EMO transducer is based on a mechanical oscillator which simultaneously acts as one of the mirrors for an optical cavity and one of the electrodes for a capacitor in an LC circuit. The resultant opto-mechanical coupling and electro-mechanical coupling, in principle, enables us to up-convert the rf signal generated in the LC circuit into the optical signal with minimum added noise that quantum mechanics allows.
We have been studying the EMO transducers for optically detecting nuclear magnetic resonance and demonstrated the proof-of-principle EMO-NMR detection[1,2]. However, the performance of EMO-NMR detection is so far inferior to the conventional electrical NMR detection.
To improve the EMO transducers, we are exploring the possibility of incorporating metasurface structures on a dielectric membrane, which would significantly enhance the reflectivity of the membrane and avoid the system heating, instead of a metal mirror. This would make it possible to use the dielectric part of the membrane as a low-loss mirror. In this presentation, I explain the theoretical background of the EMO-transducers and report my progress on it.
 Y. Tominaga, K. Nagasaka, K. Usami, and K. Takeda, J. Magn. Reson. 298, 6 (2019).
 K. Takeda et al., Optica 5, 152 (2018).
 X. Chen et al., Light: Science & Applications 6, e16190 (2017).
|氏名： 市川 弘貴
指導教員名： 香取 秀俊 教授
発表題目（英語）： A new optical lattice clock based on superradiance.
要旨（英語）： Conventional atomic clocks, including optical lattice clocks, measure time precisely by keeping the absolute frequency of the oscillator constant through feedback control based on atomic spectroscopy on clock transition. Such an atomic clock is called a passive atomic clock. On the other hand, atomic clock can be realized by utilizing the radiation from atoms as an oscillator. This type of atomic clock is called active atomic clock.
One important problem to realize active clock is a trade-off between frequency uncertainty of radiation and intensity of radiation. One possible way to overcome this challenge is superradiance.
Superradiance is a collective atomic enhancement effect. A collection of atoms interacting with common light field radiates more strongly than independent atoms because collective atomic dipole stores the coherence and then atoms radiates cooperatively. Thus we can obtain strong enough and spectral pure radiation. This type of light source is called superradiant laser.
In this presentation, I present an overview of superradiant laser, the approach we are taking, and the progress we have made so far.
|氏名： 海老野 哲朗
指導教員名： 賀川 史敬 准教授
発表題目（英語）： Interplay between topological transport and thermal fluctuation in Skyrmion lattice of MnSi
要旨（英語）： Electrons passing through spin textures with scalar spin chirality obtain Berry phase, and thus behave as if they were in a magnetic field. Because magnetic skyrmion lattice is one of the typical spin textures with scalar spin chirality, such emergent magnetic field is experimentally observed as topological Hall effect (THE), which is an additional contribution to Hall resistivity, in skyrmion-hosting materials. In the chiral magnet MnSi, THE varies with temperature by one order of magnitude whereas the skyrmion density approximately stays constant. Because based on the Berry phase picture the strength of emergent magnetic field is expected to be proportional to density of magnetic skyrmions, the temperature dependence of THE suggests a non-trivial interaction between localized spins and conduction electrons. Therefore, we are measuring the Nernst effect to clarify the influence of the emergent magnetic field on the conduction electrons from the point of view of thermoelectric transport. In this presentation, we will introduce the topological Nernst effect (TNE), which is the Nernst effect originating from the emergent magnetic field, and discuss the influence of thermal fluctuations on the emergent magnetic field on the basis of the experimental results of the temperature-dependent THE and TNE.
|氏名： 稲垣 宗太朗
指導教員名： 川﨑 雅司 教授
発表題目（英語）： Growth of Iodide thin films by molecular beam epitaxy for shift current application
要旨（英語）： Crystals with broken inversion symmetry, as typified by ferroelectric materials, are known to show photovoltaic effect. Recently, the origin of this effect is theoretically revealed to be so-called the shift current driven by the Berry phase. With bulk single crystals of a representative ferroelectric semiconductor SbSI, shift current was observed and revealed the importance of electrode. For the application of shift current, SbSI thin films whose polarization axis orders normal to the substrate plane are needed. In addition, CuI thin films which has smooth surface are needed as a transparent electrode.
In this presentation, I will briefly introduce shift current and will report the result of thin films fabrication using molecular beam epitaxy. Regarding SbSI thin films, we obtained thin films whose polarization axis orders normal to the substrate plane and confirmed that they show optical spectrum and ferroelectricity like the bulk crystals. Regarding CuI thin films, we obtained thin films which shows step terrace structure and discuss the influence of substrate.