応用物理学輪講 I
10月15日
[注意事項]
発表の10日前までに office[at]ap.t.u-tokyo.ac.jp 宛てに「氏名」「指導教員」「発表題目(英語)」「要旨(英語)」「発表言語(英語または日本語)」を送付して下さい。
発表日
2021年10月15日(金)16:50〜

Aグループ

座長
川﨑 彬斗
指導
教員名
古澤 明 教授
座長
熊崎 紘介
指導
教員名
沙川 貴大 教授
発表者名 王 佳晨
指導教員名 為ヶ井 強 准教授
発表題目(英語) Pinning Properties and Critical Current Densities in 90 K-phase and 60 K-phase YBa2Cu3O7 with Splayed Columnar Defects
要旨(英語)  Enhancement of critical current density (Jc) was observed in cuprate superconductors with columnar defects (CDs) introduced by heavy-ion irradiation [1], and further enhancement was reported by splaying the direction of CDs [2]. In the case of 90 K-phase YBa2Cu3O7 with splayed CDs, the enhanced Jc drops suddenly at around 40 K, which is interpreted to be caused by the excitation of double kinks traversing neighboring CDs [2]. Besides the optimal 90 K-phase, where the superconductivity dominates, there is another stable 60 K-phase, where the charge-density wave competes with the superconductivity. In this study, we irradiated the 90 K-phase crystals by both 800 MeV Xe and 2.6 GeV U ions, while the 60 K-phase crystals were irradiated by 800 MeV Xe ions. After introducing the splayed CDs by the irradiation, Jc was evaluated magnetically using a SQUID magnetometer with the help of the Bean model.
 Temperature dependences of Jc at H = 10 kOe in 90 K-phase YBa2Cu3O7 introduced with splayed CDs at various angles by 2.6 GeV U irradiations (B_Φ=2 T+2 T) are shown in Fig. 1(a). Consistent with the previous study [2], Jc shows a step-like decrease at around 35 K in all samples. The Jc value at 5 K as a function of splay angle (θ_CD) is shown in Fig. 1 (b). Also, a sharp increase of Jc at θ_CD = 5˚ is reproduced like that reported in Ref. [2]. We will also characterize the Jc behavior of 60 K-phase YBa2Cu3O7 with splayed CDs, and compare the results with those in 90 K-phase YBa2Cu3O7.

1. L. Civale et al., Phys. Rev. Lett. 67, 648 (1991).
2. L. Krusin-Elbaum et al., Phys. Rev. Lett. 76, 2563 (1996).
発表言語 英語
発表者名 赤塚 駿
指導教員名 マクシミリアン・ヒルシュベルガー 准教授
発表題目(英語) noncoplanar van-der-Waals magnets
要旨(英語) There are noncoplanar magnetism like skyrmion. I want to find noncoplanar magnets in van-der-Waals materials. It hasn't been found so far. Van-der-Waals materials have a structure like 2D, so it is good for 2D magnetic reaserch. I'm reaserching DyTe3 and HoTe3 which have the possibility of noncoplanar magnet.
発表言語 日本語
発表者名 池田 侑哉
指導教員名 森本 高裕 准教授
発表題目(英語) Floquet engineering of electric polarization with two-frequency drive
要旨(英語) Electric polarization is a geometric phenomenon in solids and has a close relationship to the symmetry of the system. Here we propose a mechanism to dynamically induce and manipulate electric polarization by using an external light field. Specifically, we show that application of bicircular lights (BCLs) control the rotational symmetry of the system and can generate electric polarization. To this end, we use Floquet theory to study a system subjected to a two-frequency drive. We derive an effective Hamiltonian with high frequency expansions, for which the electric polarization is computed with the Berry phase formula. We demonstrate the dynamical control of polarization for a one-dimensional SSH chain, a square lattice model, and a honeycomb lattice model.
発表言語 日本語

Bグループ

座長
古賀 淳平
指導
教員名
石坂 香子 教授
座長
小林 拓豊
指導
教員名
吉岡 孝高 准教授
発表者名 荒木 那巨
指導教員名 関 真一郎 准教授
発表題目(英語) Magnon Shift Current
要旨(英語)  The nonlinear response of quantum materials has both fundamental and technological importance. “Shift current” is an example of such a phenomenon in materials with broken inversion symmetry. The shift current is explained by the quantum geometrical phase (Berry phase) and is attractive as a new mechanism of power generation. The shift current is expected to be generated not only through general band transitions but also through various elementary excitation processes. Among them, it has been theoretically proposed that the shift current is generated through the magnetic resonance (magnon excitation). [1]
 In my presentation, I will explain the background of these studies and describe the magnetic materials that break the inversion symmetry, especially Cu2OSeO3, which is mainly used in the experiments. Next, the method and conditions of the experiments for observing shift currents will be explained, and the results of the present observations will be presented. Finally, as a future prospect, other candidate materials and experimental approaches are discussed.

[1]: T.Morimoto and N.Nagaosa, Phys. Rev B 100, 235138 (2019).
発表言語 日本語
発表者名 飯塚 太一
指導教員名 吉岡 孝高 准教授
発表題目(英語) Design of an enhancement cavity for the second harmonic generation in the DUV towards laser cooling and precision spectroscopy of carbon atoms
要旨(英語)  Laser cooling and trapping are techniques to cool atoms to low temperature and trap them in a narrow space. These techniques have led to great advances in quantum statistics and precision spectroscopy.
Laser cooling and trapping have never been applied to carbon, whose electronic transitions from the ground state lie in the deep ultraviolet (DUV) region, although they are mature for atomic species such as alkali and alkaline earth atoms. One of the obstacles is that a sufficiently powerful and stable light source in the DUV region has become available only recently. With such a sophisticated light source, precision science of carbon can be pioneered, which will contribute to a wide range of fields not only in physics but also in chemistry and biology, in which carbon plays fundamental roles.
In this presentation, I will explain a design of an enhancement cavity for the second harmonic generation in the DUV for exciting carbon atoms. To realize the maximum conversion efficiency, it is indispensable to optimize parameters of the cavity. I will also introduce a computational framework to perform this optimization.
発表言語 日本語
発表者名 池田 直樹
指導教員名 関 真一郎 准教授
発表題目(英語) Study of magnetic skyrmion and non-reciprocal transport in polar room temperature ferromagnetic metals
要旨(英語)  Recently, magnetic materials with broken inversion symmetry have been actively studied because they are expected to display various non-trivial physics. One example is the appearance of magnetic skyrmion [1], i.e., a vortex-like swirling magnetic structure with particle nature, which is recently attracting much attention as a potential information carrier.
 Another example is the emergence of non-reciprocal transport [2], which can lead to the realization of diode for various quasi-particle flow such as conduction current, photon, magnon and phonon etc.
 In this study, we newly investigate room temperature ferromagnetic metals with polar structure. I will talk about their physical properties and possible observation of skyrmion formation and non-reciprocal transport phenomena.

[1] I. Kezsmarki, et al., Nature mat. 14, 1116 (2015).
[2] Y. Tokura, et al., Nature Comm. 9, 3740 (2018).
発表言語 日本語