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駒場生の皆さん、物理工学科へぜひお越しください。

駒場生の皆さん、物理工学科へぜひお越しください。

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  • 談話会・セミナー
  • 渡辺悠樹講師 第12回凝縮系科学賞 受賞
    2017.11.20
  •  
  • 物理工学専攻の渡辺悠樹講師が第12回凝縮系科学賞を受賞しました。受賞テーマは「空間群を用いたバンド構造のトポロジーの研究」です。
    同賞は、広い意味での凝縮系科学の研究において優れた研究業績を挙げた若手研究者に贈られるもので、平成29年11月17日に東京大学柏キャンパスにて授賞式が行われました。

    ・凝縮系科学賞

  • [開催中止]第13回 物理工学科教室談話会(講師:Leonardo Civale氏)
    2017.12.11
  •  
  • ●本日の談話会は開催中止になりました。

    日時 : 平成29年12月11日(月) 15 :00

    場所:工学部6号館大会議室
    講師:Leonardo Civale氏
    所属:Materials Physics and Applications Division, CMMS, Los Alamos National Laboratory, Los Alamos, USA
    題目:What is the lowest possible vortex creep in superconductors, and how can we achieve it?
    概要:
    Thermal and quantum fluctuations play only a minor role on the vortex properties of many conventional LTS. However, they dramatically influence vortex matter in HTS such as oxides and Fe-based, creating a proliferation of vortex liquid phases that occupy substantial portions of the phase diagram and fast dynamics of the metastable states (flux creep). This fascinating physics has been a topic of continuous interest for decades, but on the other hand is detrimental for applications. The strength of the thermal fluctuations is quantified by the Ginzburg number (Gi) that measures the ratio of the thermal energy to the condensation energy in an elemental superconducting volume. The combination of the small coherence length (x), large anisotropy (g) and high transition temperatures (Tc) in the HTS results in Gi values several orders of magnitude higher than in LTS. For instance, Gi ~ 10-9 in Nb and ~ 10-2 in YBa2Cu3O7, naturally accounting for the much faster creep rate (S) in the latter. We have found that, for strong pinning superconductors in the Anderson-Kim (A-K) creep regime, there is a universal minimum attainable S ~ Gi1/2(T/Tc). This lower limit has been achieved in a few materials including YBa2Cu3O7, MgB2 and our BaFe2(As0.67P0.33)2 films and, to our knowledge, violated by none. This hard constraint has two important, broad implications: first, the creep problem in HTS cannot be fully eliminated and there is a limit to how much it can be ameliorated, and secondly, we can confidently predict that any yet-to-be-discovered HTS will have fast creep. On the other hand, many SC exhibit S values higher, sometimes orders of magnitude higher, than the lower limit. The reason is that Gi only sets the lowest limit for S, but in order to achieve it the pinning landscape must be optimized. I will show that S can be reduced by appropriate engineering of the pinning landscape, in some cases (such as in irradiated Ba(Fe1-xCox)2A2 single crystals) dramatically so and all the way down to the lower limit imposed by Gi. Finally I will discuss some of our studies of creep outside the A-K limit and in very clean (weak pinning) samples, where collective effects are relevant and different glassy and plastic dynamic regimes can be observed and tuned by methods such as irradiation and film thinning.

    紹介教員: 鹿野田 教授、為ヶ井 准教授

お知らせ
  • 渡辺悠樹講師 第12回凝縮系科学賞 受賞
    2017.11.20
  •  
  • 物理工学専攻の渡辺悠樹講師が第12回凝縮系科学賞を受賞しました。受賞テーマは「空間群を用いたバンド構造のトポロジーの研究」です。
    同賞は、広い意味での凝縮系科学の研究において優れた研究業績を挙げた若手研究者に贈られるもので、平成29年11月17日に東京大学柏キャンパスにて授賞式が行われました。

    ・凝縮系科学賞

  • 【教養学部生対象】物理工学科見学会のお知らせ[12/16(土)]
    2017.10.19
  •  
  • 教養学部生を対象とした物理工学科見学会を開催しますので、興味のある方は是非ご参加下さい。事前申し込みは不要です。

    日時:平成29年12月16日(土)14:00-16:15
    集合場所:本郷キャンパス工学部6号館1階大会議室
    プログラム:
    14:00-14:15 学科紹介(学科長 小芦雅斗教授)
    14:15-15:15 研究室見学
    石坂研究室 – 光で拓く物質科学 –
    石渡研究室 – 極限環境を利用した強相関物質の開拓 –
    千葉研究室 – 磁性の電気的な制御 –
    15:15-16:15 先輩学生との懇親会
    (10名程度の大学院生が参加予定)

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談話会・セミナー
  • [開催中止]第13回 物理工学科教室談話会(講師:Leonardo Civale氏)
    2017.12.11
  •  
  • ●本日の談話会は開催中止になりました。

    日時 : 平成29年12月11日(月) 15 :00

    場所:工学部6号館大会議室
    講師:Leonardo Civale氏
    所属:Materials Physics and Applications Division, CMMS, Los Alamos National Laboratory, Los Alamos, USA
    題目:What is the lowest possible vortex creep in superconductors, and how can we achieve it?
    概要:
    Thermal and quantum fluctuations play only a minor role on the vortex properties of many conventional LTS. However, they dramatically influence vortex matter in HTS such as oxides and Fe-based, creating a proliferation of vortex liquid phases that occupy substantial portions of the phase diagram and fast dynamics of the metastable states (flux creep). This fascinating physics has been a topic of continuous interest for decades, but on the other hand is detrimental for applications. The strength of the thermal fluctuations is quantified by the Ginzburg number (Gi) that measures the ratio of the thermal energy to the condensation energy in an elemental superconducting volume. The combination of the small coherence length (x), large anisotropy (g) and high transition temperatures (Tc) in the HTS results in Gi values several orders of magnitude higher than in LTS. For instance, Gi ~ 10-9 in Nb and ~ 10-2 in YBa2Cu3O7, naturally accounting for the much faster creep rate (S) in the latter. We have found that, for strong pinning superconductors in the Anderson-Kim (A-K) creep regime, there is a universal minimum attainable S ~ Gi1/2(T/Tc). This lower limit has been achieved in a few materials including YBa2Cu3O7, MgB2 and our BaFe2(As0.67P0.33)2 films and, to our knowledge, violated by none. This hard constraint has two important, broad implications: first, the creep problem in HTS cannot be fully eliminated and there is a limit to how much it can be ameliorated, and secondly, we can confidently predict that any yet-to-be-discovered HTS will have fast creep. On the other hand, many SC exhibit S values higher, sometimes orders of magnitude higher, than the lower limit. The reason is that Gi only sets the lowest limit for S, but in order to achieve it the pinning landscape must be optimized. I will show that S can be reduced by appropriate engineering of the pinning landscape, in some cases (such as in irradiated Ba(Fe1-xCox)2A2 single crystals) dramatically so and all the way down to the lower limit imposed by Gi. Finally I will discuss some of our studies of creep outside the A-K limit and in very clean (weak pinning) samples, where collective effects are relevant and different glassy and plastic dynamic regimes can be observed and tuned by methods such as irradiation and film thinning.

    紹介教員: 鹿野田 教授、為ヶ井 准教授

  • もっと詳しく
  • 第16回 物理工学科教室談話会(講師:Prof. Dr. Friedhelm Bechstedt)
    2017.12.07
  •  
  • 日時:平成30年1月9日(火)15:00~16:30
    場所:工学部6号館3階 372 (セミナー室C)
    講師:Prof. Dr. Friedhelm Bechstedt
    所属:University of Jena, Germany
    題目:Topological surface and interface states from first principles
    概要:
    Topological insulators (TIs) have opened a new fascinating field for solid-state physicists. They are based on small-gap semiconductors with large spin-orbit interaction (SOI). At their surfaces and interfaces metallic edge states with linear bands (Dirac cones) and spin polarization are formed. Two classes of TIs are investigated, (i) the three-dimensional (3D) zero-gap semiconductors -Sn and HgTe with inverted bands, and (ii) two-dimensional (2D) graphene-like honeycomb crystals such as germanene, their chemically functionalized derivatives, and their one-dimensional (1D) nanoribbons. Topological invariants are computed ab initio. Thereby, quasiparticle effects are important for the correct band ordering. The boundary states of -Sn surfaces [1a] and -Sn or HgTe quantum well interfaces formed with CdTe (see Fig. 1) [1b, c, d] are investigated with respect to the appearance of topological states, their localization and spin polarization. We demonstrate that the graphene-like, buckled group-IV-derived crystals with small gap and strong SOI realize the quantum spin Hall (QSH) phase [2a, b, c]. Their ribbons indeed show topological edge states [2b], which however influence the quantization of the spin Hall conductivity [2c]. The conservation of the topological character of the 2D systems is discussed after deposition on passivated or graphene-covered SiC substates [3a, b].
    [1] S. Küfner, F.B., et al., Phys. Rev. B 90, 125312 (2014); 89, 195312 (2014); 91, 035311 (2015); 93, 045304 (2016).
    [2] L. Matthes, F.B., et al., Phys. Rev. B 93, 121106(R) (2016); 90, 165431 (2014); 94, 085410 (2016).
    [3] F. Matusalem, F.B., et al., Phys. Rev. B 94, 241403(R) (2016); Scientific Reports 7, 15700 (2017).

    紹介教員:押山 淳 教授、今田 正俊 教授

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