座長：倉田 伊織、渡邉 伊吹
|氏名： 大塚 悠介
指導教員名： 十倉 好紀 教授
発表題目（英語）： Magneto-transport phenomena related to spin-orbit coupling in a narrow-gap insulator
要旨（英語）： B20-type FeSi with a chiral crystal structure is a nonmagnetic semiconductor with a narrow bandgap of several tens of meV. However, it has been reported that magnetic susceptibility and electrical resistance exhibit unusual behaviors that cannot be predicted from the calculated bulk band-structure and have been discussed in terms of a Kondo insulator. We focus on and have scrutinized those properties through the thin-film growth of FeSi and the systematic measurements of magneto-transport properties. In this presentation, I will introduce the various characteristic transport properties originating from the peculiar magnetic state of FeSi and discuss their relations to the strong spin-orbit coupling.
|氏名： 加藤 喜大
指導教員名： 高橋 陽太郎 准教授
発表題目（英語）： Terahertz and infrared magneto-optical spectroscopy of the ferromagnetic nodal-line semimetal candidate Fe3GeTe2 thin film
要旨（英語）：Topological semimetals host electronic structures with several band-contact points or lines and are generally expected to exhibit unique topological responses. Anomalous Hall effect (AHE) is one of them, and in fact some topological materials show giant AHE. It is considered that this is attributed to Berry curvature generated from band-contact points or lines. From another perspective, giant AHE can be thought of as DC limit of resonances in Hall conductivity spectrum due to optical transition near band-contact points. Hall conductivity spectrum can be measured by magneto-optical effects such as Faraday effect and magneto Kerr effect. Therefore, we can clarify the origin of AHE by magneto-optical spectroscopy.
Fe3GeTe2 (FGT) is a candidate for ferromagnetic nodal line semimetal, in which the conduction and the valence bands cross each other along a one-dimensional curve. FGT shows large AHE (Hall angle ~ 10%), and this is thought because of Berry curvature from nodal line. Therefore, it is expected that a resonance appears in Hall conductivity spectrum due to optical transition near nodal line.
In this presentation, I will introduce AHE and magneto-optical effect and talk about the result of terahertz and infrared magneto-optical spectroscopy of FGT.
|氏名： 大野 瑞貴
指導教員名： 川﨑 雅司 教授
発表題目（英語）： Quantum transport of magnetic topological semimetal EuSb_2 films
要旨（英語）： Topological semimetals (TSMs) are characterized by nontrivial band crossing through nodal points in momentum space. Another class of TSMs have attracted attention, the topological nodal line semimetals (TNLSMs), which have band crossing at nodal lines. Spin-orbit coupling readily gaps out the nodal lines at low symmetry points, but nodal lines are preserved under certain crystalline symmetry. CaSb_2 has proposed as TNLSMs by calculations. We focus on an antiferromagnet EuSb_2 which has the same nonsymmorphic symmetry as CaSb_2 . The magnetic structure of EuSb_2 , corresponding magnetic space group /P/_a 2_1 //m/, does not break the two-fold screw symmetry (2_1 //m/) that protects the nodal lines. Thus, EuSb_2 can be a magnetic TNLSM. For elucidating and controlling its topological quantum state, fabrication of ﬁlms have been highly desired. We fabricate single crystalline EuSb_2 thick films by using molecular bean epitaxy (MBE). In magneto-transport, we observe quantum oscillations with multiple oscillation frequencies and show a two-dimensional ﬁeld-angle dependence even in the 250 nm thick ﬁlms.
In this presentation, I will briefly introduce TNLSMs and then discuss crystallinity and quantum transport properties of EuSb_2 films.
|氏名： 加納 正太郎
指導教員名： 中村 泰信 教授
発表題目（英語）： Quantum Transducer with Surface Acoustic Wave.
要旨（英語）： Quantum computing, which can dramatically improve computational power for certain tasks, has been attracting much attention recently. Among the several possible platforms for quantum computing, the superconducting circuits is one of the most advanced systems and have been developed by a number of universities and companies. In order to perform a meaningful calculation with superconducting qubits, it is necessary to increase the number of qubits.
Currently, the number of qubits in one chip is less than 100. Thus, one can implement them in a single dilution refrigerator, but as the system becomes larger it would be necessary to connect systems between different refrigerators.
It is relatively easy to extract the quantum information from a superconducting qubit to a microwave photonic qubit. However, since the energy of a microwave photon is much less than that of the room-temperature thermal fluctuations, the quantum information is quite vulnerable if one extracts it out of a refrigerator in a form of microwave. One solution for this problem is to convert microwave into light. The large energy of an optical photon allows preservation of information even at the room temperature. The system which performs coherent conversion between microwave and optical photons is called quantum transducer. There are several physical systems explored for the quantum transducer, and one of them is a surface acoustic wave (SAW).
I will explain how we are to demonstrate quantum transducer with SAW.
|氏名： 岡田 尚貴
指導教員名： 山地 洋平 特任准教授
発表題目（英語）： Spectral function of many-body fermions in continuum space by variational Monte Carlo method
要旨（英語）： To calculate spectral function of many-body fermions in continuum space is an efficient way to see electron correlation in a strongly correlated system.
It tells us physical properties such as band dispersion, effective mass, lifespan of a quasiparticle, satellite peak, and effects of electron correlation on the stabilization of Wigner crystal, which are all important in understanding strong correlation effects.
There are several studies which are related to electron correlation of many-body fermions in continuum space.
An example is the study about the calculation of band dispersion and effective mass of a quasi-particle in a weakly correlated system. [1,2]
Another example is the study, in which the spectral function in metallic region was calculated by using Feynman diagram development, and a secondary plasmon satellite was confirmed. 
However, application of these methods to strongly correlated systems is difficult because in the first study, interaction between quasi-particles wasn’t taken into account and there is a limit to precisely computable orders of perturbation in Feynman diagrammatic method used in the second study, which will prevent an accurate calculation of spectral function in a strongly correlated system.
Meanwhile, there is a possibility that electron correlation in strongly correlated systems can be confirmed accurately through a calculation of spectral function using variational Monte Carlo (VMC) method because it uses high-precision Hilbert space which can be constructed from excited states.
In fact, this method succeeded in calculating a spectral function accurately in lattice models such as Hubbard model. [4,5]
Therefore, we decided to apply this method to calculation of spectral function in continuum space and try to see electron correlation in strongly correlated systems.
In this talk, I will explain the details of application of VMC to this problem, some preliminary results.
 N. D. Drummond and R. J. Needs, Phys. Rev. B 79, 085414(2009)
 N. D. Drummond and R. J. Needs, Phys. Rev. B 80, 245014(2009)
 Y. Pavlyukh, et al, Phys. Rev. Lett. 117, 206402(2016)
 Tao Li and Fan Yang, Phys. Rev. B 81, 214509 (2010)
 Kota Ido, Masatoshi Imada, Takahiro Misawa, Phys. Rev. B 101, 075124(2020)
|氏名： 神田 朋希
指導教員名： 小濱 芳允 准教授
発表題目（英語）： Symmetry lowering on the field-induced commensurate phase in CeRhIn5
要旨（英語）： CeRhIn5 is one of the prototypical Ce-based heavy-fermion systems. Recently, an electronic nematic state was discovered in CeRhIn5 when the external magnetic field of ~ 30 T was applied with a tilting angle from the  axis . In this state, the electronic properties show two-fold symmetry without lowering the four-fold symmetry of the crystal structure. The previous neutron scattering measurement suggests that this state may derive from its peculiar magnetic structure . To study the relationship between the magnetic structure and the nematic state, we performed the NMR experiment on CeRhIn5. In this presentation, I will give a brief introduction of this compound and discuss the origin of the nematic state based on our experimental results.
 F. Ronning et al., Nature, 548, 313 (2017).
 D. M. Fobes et al., Nat. Phys. 14, 456 (2018).
|氏名： 久保田 樹
指導教員名： 岩佐 義宏 教授
発表題目（英語）： Optical properties of exfoliated CrCl3 crystals
要旨（英語）： Two-dimensional van der Waals crystals and van der Waals heterostructures are unique material platforms of exotic electronic, optical and magnetic functionalities. For example, several van der Waals crystals are known to show layer-dependent electric/optical properties, valley-related phenomena, and characteristic exciton physics. Among them, van der Waals magnets are attracting much attention due to the peculiar magnetic properties which are distinct from bulk.
In this presentation, I will report the electromagnetic wave response of CrCl3, one of the van der Waals insulating antiferromagnet, in visible light and microwave region. Thickness-dependent photoluminescence and the magnetic resonance of exfoliated CrCl3 are presented. I will also discuss the future experiment about the van der Waals heterostructure using CrCl3.