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応用物理学輪講 Ⅰ

        
2017年6月9日(金)16:50~ 
62号講義室(2F) 
 座長:森 亮介、安井 伸
64号講義室(2F)  
座長:三石 夏樹
氏名: 大坪  舜
指導教員名: 沙川 貴大 准教授
発表題目(英語): Information thermodynamics in gene regulatory network motifs
要旨(英語): Looking at chemical reaction networks in living systems, one can soon realize that they are not random networks. There exist some specific components that appear statistically significantly. Such specific components are called network motifs, which have attracted much attention in systems biology since 2002. In particular, wide range of studies have conducted on what properties distinguish network motifs from other rare network patterns.
 On the other hand, information thermodynamics is a theoretical framework which generalizes nonequilibrium thermodynamics to stochastically fluctuating systems with information flow.
 I have studied network motifs in gene regulatory networks from an information thermodynamics perspective. It is known that only a feedforward type is the network motif among several three node patterns. In this presentation, I will pick up two well-known three node network patterns, feedforward type and feedback type, and try to explain why feedforward type is superior to feedback type in an information thermodynamics sense.
発表言語: 英語
氏名: 大森  遼
指導教員名: 志村 努 教授
発表題目(英語):  The characteristics of recording and reconstruction for time series phase modulated collinear holographic memory
要旨(英語):  rate than conventional optical memories.
Now, I propose a new system of holographic memories named “time series phase modulated collinear holographic memory(TPCH)”. For normal holographic memory, information is coded in 2 dimensional digital data pages, and each page is recorded and reconstructed independently. On the other hand, for time series holographic memory, information is coded as multi-channel continuous signal, which makes recording density higher.
 In our laboratory, time series intensity modulated collinear holographic memory(TICH) has been studied. The only difference of TICH and TPCH is how to present the information. For TICH, signal is presented by the intensity of the light, that is whether the light is ON or OFF. On the other hand, for TPCH, the intensity of the light is constant and signal is presented by the phase of the light, for example 0 or pi. In this presentation, I will introduce the distinctive feature of TPCH compared to TICH given by the simulation.
発表言語: 日本語
氏名: 大橋  由季
指導教員名: 福谷 克之 教授
発表題目(英語): Two-photon photoemission spectroscopy (2PP) of TiO2 surfaces
要旨(英語):  TiO2 is an insulating material with a bandgap of 3.2 eV, which finds a variety of applications such as hydrogen sensors and photocatalysis. The electronic ground states of TiO2 surfaces has been well studied by photoemission spectroscopy. On the other hand, the electronic excited states which contribute to the reaction processes directly have not been explored. We have developed two-photon photoemission spectroscopy (2PP) which allows for observing the electronic excited states. We took 2PP spectra at rutile TiO2(110) surfaces with oxygen vacancies by changing the excitation light energy between 3.4 eV and 3.9 eV. We observed a feature at a kinetic energy of 1.8 eV, which is found to take a maximum intensity at a light energy of 3.4 eV. This feature corresponds to the resonance between the excited state at 2.6 eV above Fermi level (EF) and the defect state induced by oxygen vacancies at 0.8 eV below EF. I will also report on the TiO2/hydrogen interfaces, which is known to have the defect state as well, and discuss the characteristic feature of the electronically excited state of TiO2.
発表言語: 日本語
氏名: 奥村  駿
指導教員名: 求 幸年 教授
発表題目(英語):  Chiral soliton lattice in itinerant electron system
要旨(英語):  Magnets with chiral lattice structures often show interesting properties associated with their peculiar spin textures. In many cases, the spin textures acquire topological nature, and hence, are robust against perturbations.  A typical example is a chiral soliton lattice, which was recently found in a monoaxial chiral magnet CrNb3S6. While the compound shows a helical spin spiral at zero magnetic field, it turns into a chiral soliton lattice in a magnetic field perpendicular to the chiral axis. The chiral soliton lattice has a spin texture like a ribbon twisted in part, whose period changes continuously with the magnetic field. Interestingly, the electrical resistivity decreases in accordance with the evolution of the chiral soliton lattice, suggesting strong interplay between the peculiar spin texture and electronic properties. While the chiral soliton lattice has been studied theoretically, such interplay remains elusive.
 In the present study, in order to clarify the interplay between magnetism and electronic transport in such monoaxial chiral magnets, we investigate a minimal itinerant electron model, a one-dimensional Kondo lattice model with the Dzyaloshinskii-Moriya interaction. We study the magnetic and electronic properties of this model by using a quantum Monte Carlo simulation at finite temperature.
 We show that the model exhibits a helical order at zero magnetic field, whose period depends on the spin-charge coupling, the Dzyaloshinskii-Moriya interaction, and the electron filling. Once the magnetic field is applied, we clarify that the helical state turns into the chiral soliton lattice, which reduces its soliton density as the magnetic field increases. While further increasing the magnetic field, the chiral soliton lattice eventually changes into a forced ferromagnetic state. We find that the system exhibits negative magnetoresistance, which is closely related to the number of solitons at low temperature. While changing temperature, we find that the chiral soliton lattice is melted by thermal fluctuation and the electrical resistivity is increased. We discuss our results in comparison with the experimental results in CrNb3S6.
発表言語: 英語 
氏名: 大原 健 悟
指導教員名: 長谷川 幸雄 准教授
発表題目(英語): STM observation of the surface structure of Mn3Sn
要旨(英語): The anomalous Hall effect has been observed typically in ferromagnetic materials. Recently, however, it is observed in antiferromagnetic materials. Here, I will introduce Mn3Sn as an example of antiferromagnetic materials that exhibit the anomalous Hall effect. In order to investigate the origin of the phenomenon, I am studying the structure of cleaved Mn3Sn surfaces by using scanning tunneling microscopy (STM). In this presentation, I’ll talk about how to observe the surface structure by STM and what kinds of structure are expected on the surface. 
発表言語: 日本語
氏名: 小坂 雄大
指導教員名: 石渡 晋太郎 准教授 
発表題目(英語): Structural and physical properties on new perovskite cobalt oxides Sr_1-x_Ca_x_CoO_3 
要旨(英語): Strongly correlated electron systems have attracted a lot of researchers because of their various features. These properties originate from electorons’ interactions whose influences cannot be negligible. Transition metal oxides with perovskite structures are good examples of such a system. Their properties are easy to control by changing structural parameters or chemical doping. In this presentation I introduce SrCoO3, which is known as a ferromagnetic material with a cubic perovskite structure, and show how its magnetic properties change with doping Ca in Sr site. Finally, a new perovskite CaCoO3 was successfully synthesized. It has a new magnetic phase. 
発表言語: 日本語 

 
 

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