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応用物理学輪講 Ⅰ

        
2017年9月29日(金)16:50~ 
62号講義室(2F) 
 座長:上田 健人
64号講義室(2F)  
座長:稲垣 雄介
氏名: 三石  夏樹
指導教員名: 石坂 香子 准教授
発表題目(英語): Electronic structures of layered transition metal dichalcogenide VTe2 with double zigzag chains
要旨(英語): Layered transition metal dichalcogenides (TMDs) have been studied for their rich physical properties such as charge density wave, superconductivity, thermoelectricity, magnetoresistance, valleytronics and so on. In spite of considerable researches on TMDs, few investigations on group-V ditellurides MTe2 (M = V, Nb, Ta) are reported until now. These compounds form the common monoclinic (1T") structure with double zigzag chains of metal atoms within each layer. In particular, VTe2 shows the structural phase transition at around Ts = 480 K on cooling, from the trigonal 1T phase to the monoclinic 1T" phase, which accompanies the large atomic displacements (maximum: ∆a/a ~ 9%). However, the mechanism of this phase transition is not revealed yet.
 To clarify the modification of electronic states on 1T-1T" phase transition, we performed ARPES (Angle-Resolved PhotoEmission Spectroscopy) measurements and first-principles calculations on 1T (1T")-VTe2. Although observed band structures in 1T phase are in good agreement with the band calculation, anomalous momentum-independent flat bands appear in 1T" phase, which are not observed in 1T phase. Despite such drastic reconstructions of bulk electronic structures via the transition, some topological nontrivial surface states, which are theoretically predicted in the 1T phase, still survive in the 1T" phase. In this presentation, I will report these peculiar electronic structures in detail and discuss the origin of them.
発表言語: 日本語
氏名: 森  亮介
指導教員名: 中村 泰信 教授
発表題目(英語):  Quantum transducer with ferromagnet and atomic spin ensemble
要旨(英語):  Frequency conversion between microwave photons and optical photons is an essential component in large scale quantum network because microwave photons are carrier of information processed by superconducting qubits and optical photons realize long-distance, robust information distribution. Quantum system interacting with both of them enables this conversion indirectly, and such system is called quantum transducer.
 Recently, our team realized quantum transducer with magnons, collective spin excitations in ferromagnet. Although strong coupling with microwave photons was achieved, very weak coupling with light led to very low conversion efficiency. In my work, as another approach, quantum transducer with magnons and atomic gas ensemble is considered. In this system, strong coupling of atoms with light and strong coupling of magnons with microwave are merged and conversion efficiency is supposed to increase, if interaction between magnons and atoms exists. Therefore first step of my work is to observe this interaction.
In this presentation, first I will introduce background information, and next I will talk about current progress.
発表言語: 日本語
氏名: 安井  伸
指導教員名: 嶽山 正二郎 教授
発表題目(英語): Solid state physics of volborthite under ultra-high magnetic fields
要旨(英語):  Frustrated quantum magnets have attracted much attention for realizing spin liquid. There are three representative frustrated magnets, triangle, pyrochlore, and kagome. Kagome lattice is the structure which spin liquid is appeared not only at ground state but also in magnetic field 
Volborthite Cu3V2O7(OH)2・2H2O has s=1/2 distorted Kagome lattice. Because of the certain imperfections tend to obscure the intrinsic properties, several spin models have been proposed and an appropriate spin model has not been decided yet.
 My purpose is to specify the appropriate spin model from experimental approach. Magnetic field that can saturate with the magnetization of volborthite is very high. So using destructive generation of magnetic field is only way which can measure the saturated magnetization of volborthite. To accomplish my purpose, I made the poly vinyl alcohol films that include single crystals of volborthite and measured absorption spectra for the Faraday rotation measurement.
発表言語: 日本語
氏名: 山崎  翔太
指導教員名: 中村 泰信 教授
発表題目(英語):  Tunable-waveform microwave single-photon generation using a superconducting qubit
要旨(英語):   Superconducting qubits attract more and more attention as one of the key components for the quantum computers. Many reseachers are concentrating on integrating superconducting qubits into small architectures with the aim to realize large scale quantum computation. On the other hand, it is also important to establish communication protocols between superconducting qubits which are separated each other spatially. Traveling microwave photons are able to transport the informations of the qubits. The technique to shape the wave form of the microwave photon is required to communicate between qubits efficiently. In addtion, the teqnique can also be applied to generating time-bin qubits, which can detect the transmission losses of the traveling single photon. In this presentation, I will introduce the basis of superconducting qubits and the method to generate arbitrary wave form traveling microwave single photons, and show you the recent experimental results.
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