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応用物理学輪講 Ⅰ

        
2017年7月7日(金)16:50~ 
62号講義室(2F) 
 座長:管 一澄、浅井 遼
64号講義室(2F)  
座長:秋葉 智起
氏名: 田中  未羽子
指導教員名: 樽茶 清悟 教授
発表題目(英語): Valley current in correlated insulating state in graphene
要旨(英語): Electron in graphene has degree of freedom in momentum space, "valley". When band gap is open in graphene band structure, each valley have opposite chern number. This topological feature cause "valley Hall effect" which is similar to spin Hall effect.
 In order to detect Valley Hall effect, we have to open a gap in fermi energy. In previous research,they applied external electric field or substrate lattice potential to do it. But e-e interaction is also able to open a gap.
 I detected valley Hall effect in LAF(layer anti ferromagnetic) state. This LAF state appear in quantum Hall regime and it has a gap due to e-e interaction. Its interesting point of is that it can be used as valley / spin exchanger. I'll talk about the idea of this experiment and recent exp
発表言語: 日本語
氏名: 林  洋平
指導教員名: 千葉 大地 准教授 
発表題目(英語):  Correlation between strain and control efficiency of electric field effect on magnetic anisotropy in Pt/Co/Pd system
要旨(英語):  Electric field (EF) effect on magnetic anisotropy has been intensively studied because of its potential for reduction of energy consumption of magnetic memory devices. However, a significant improvement in control efficiency is indispensable before putting this effect into use. Recently, our group reported that the perpendicular magnetic anisotropy (PMA) can be modulated by applying EF on the Pd surface in the Pt/Co/Pd system deposited on a GaAs (001) substrate. Moreover, strong temperature dependence of the modulation is observed. One possible origin of this is a temperature dependent lattice strain, which is caused by the difference in the thermal expansion constants between the Pd layer and a GaAs substrate, and resultant change in the electronic structure in the Pd layer. In order to confirm this internal effect, we examined the EF effect on PMA in the same system deposited on a Si substrate.
 In this presentation, I will introduce the substrate dependence of EF effect on PMA by comparing samples deposited simultaneously on a GaAs and a Si substrate. In addition, my next attempt to clarify the correlation between strain and EF effect will be explained.
発表言語: 日本語
氏名: 中澤  佑介
指導教員名: 川﨑 雅司 教授
発表題目(英語): Growths and transport properties of Dirac semimetal Cd3As2 thin films
要旨(英語):  Topological semimetals have attracted great attentions owing to their unique physical properties originating from band topologies. Topological semimetals can be classified into Dirac and Weyl semimetals depending on symmetries of systems such as time-reversal symmetry (TRS), space inversion symmetry (SIS) and crystal symmetry.
 Cd3As2 is known as a topological Dirac semimetal (TDS), which possesses both TRS and SIS. In Cd3As2 system, three dimensional Dirac fermions and a non-trivial surface state named Fermi arcs are realized, which are stabilized by four-folded rotational symmetry of its crystal structure. Besides these unique properties, TDS is expected to be an ideal platform for many other quantum states, e.g. Weyl semimetal, topological insulator and topological super conductor when a certain symmetry is broken.
  We have worked on fabrications of high quality Cd3As2 thin films and investigations about its quantum transport properties. In this talk, first, I will introduce basic characters of topological materials especially TDS. Then, the details about growth of Cd3As2 thin films will be reported. Finally, we will see their transport properties.
発表言語: 英語
氏名: 広谷  渉
指導教員名: 伊藤 伸泰 准教授
発表題目(英語):  Analysis of noun bigram in Aozora Bunko
要旨(英語): Can we get semantic relation among words automatically from texts through analysis with a computer? To learn the meaning of word from text is a main problem to solve.  
 In order to let computer read as much texts as possible , we take Aozora Bunko (copyright-free Japanese biggest literatures database). we use MeCab (morphological analysis software) to divide texts into parts of speech. And then we count the frequency of general nouns. We also count frequency of directed pairs of general nouns.
 As a result, a rank-frequency curve turns out to have two inflection points.
We can classify nouns under 3 types by these inflection points.  
 Frequency of directed pairs of general nouns have more information. The expected value of  frequency of the directed pair of (A->B) can be estimated by frequency of A and B. There is large difference between actual value and expected value. We made score to evaluate deviance from expected value. Score distribution consists of a gaussian part and an exponential part. This score distribution proved that some directed pairs emerge much more(less) than the expected values. It is non-trivial phenomenon. Outstanding directed pairs may have some relation from points of meaning.
 Irreversibility of words-pair is also interesting. For example, the number of pairs (右->左) is significantly larger than that of pairs (左->右). This asymmetry may reflect order of words in Japanese text.
発表言語: 日本語 
氏名: 西野  隆太郎
指導教員名: 川﨑 雅司 教授
発表題目(英語):  Electric field induced surface conduction in ferroelectric PbTiO3
要旨(英語): Electrostatic doping by field effect transistors (FETs) is a common way to control carrier density and the electronic properties of materials. However, due to the gate dielectric breakdown, carrier density that FETs structure can change is only ~ 5×1012 cm-2. Electric double layer transistor (EDLT) which uses electrolyte as gate materials overcomes this problem. It can accumulate large carriers ~ 4×1014 cm-2­. This large carrier accumulation enables us to modulate electronic properties drastically such as insulator to superconducting transition in KTaO3­.
 In this study, we used ferroelectrics as a channel. Recently, interaction between mobile carrier and ferroelectricity has attracted attention as it may induce fascinating physical properties such as superconductivity or surface charges of ferroelectric single crystal. Here, we successfully induced surface conductivity in ferroelectric PbTiO3. At 300K, we obtained high sheet carrier concentration ~ 5.0 × 1013 cm-2 which is above the maximum value achieved in conventional metal-oxide-semiconductor FET (~1.0 × 1013 cm-2)
発表言語:  日本語
氏名: 福原 竜 馬
指導教員名: 志村 努 教授 
発表題目(英語): Novel measurement method for optical torque acting on nano structure
要旨(英語):
要旨(英語): We have analyzed the optical torque on the plasmonic nano structure, and discovered the torque on V-shaped nano structure has a rotation axis different from the optical axis. To experimentally observe and analyze the torque, we have been developing a novel method to measure optical force and torque acting on nano structures, which takes advantage of micro machine. In the presentation, we introduce this method and proceedings.
発表言語: 日本語 

 
 

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