応用物理学輪講 I
10月8日
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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8日(金)16:50〜

Aグループ

座長
越智 友崇
指導
教員名
長田 俊人 教授
座長
加藤 啓輔
指導
教員名
中村 泰信 教授
発表者名 周 芝苑
指導教員名 中島 多朗 准教授
発表題目(英語) magnetic-field-induced phases in centrosymmetric skyrmion-host Gd compounds investigated by quantum beams
要旨(英語)  Magnetic skyrmions, topologically-protected vortex-like spin structures, had been considered to appear only in chiral magnetic materials such as MnSi. [1] But recently, skyrmions have also been discovered in centrosymmetric Gd-compounds, such as Gd2PdSi3, GdRu2Si2, and Gd3Ru4Al12.[2,3]
 We studied a Gd compound with a tetragonal crystal structure and it exhibits several magnetic phase transitions in a c-axis magnetic field at low temperature. Especially, Hall effect anomalies have been observed in several field-induced phases, suggesting the possibility of magnetic skyrmion phases. [4]
 In this study, we utilized quantum beams to clarify the magnetic structure of possible skyrmion phases in the Gd compound. Generally, Gd has an extremely large neutron absorption cross section, and therefore it is difficult to investigate by neutron scattering. But the neutron absorption of Gd decreases when the incident neutron energy exceeds approximately 100 meV. We thus performed neutron scattering experiments at the BL12 HRC spectrometer in J-PARC, at which the high energy incident neutron beam is available and found that the field-induced phases have incommensurate magnetic modulation wave vectors (q-vectors). In addition, in order to investigate the spin components corresponding to each magnetic modulation wave vector, we conducted a resonant X-ray magnetic scattering at BL-3A in KEK Photon Factory.

[1]Y.Tokura and N.Knazawa, Chem. Rev. *121*(5), 2857-2897(2021)
[2]T.Kurumaji *et al*. Science. *365*, 914-918(2020)
[3]N.D.Khanh *et al*. Nat. Nanotechnol. *15*, 444-449(2020)
[4]吉持遥人他 日本物理学会 第76回年次大会(2021年) 口頭発表 12aC1-3
発表言語 日本語
発表者名 吉持 遥人
指導教員名 関 真一郎 准教授
発表題目(英語) Realization of versatile spin textures in a centrosymmetric tetragonal skyrmion-hosting magnet
要旨(英語)  Magnetic skyrmions, topologically protected spin swirling structures, have attracted attention for next-generation magnetic memory applications.
Previously, extensive studies have successfully identified skyrmion-hosting materials with non-centrosymmetric systems. These asymmetries cause the relativistic Dzyaloshinskii-Moriya (DM) interaction, which inherently prefers twisted spin configurations and plays a crucial role in the skyrmion formation.
 Recently, however, skyrmions have been observed in centrosymmetric Gd compounds accompanied with the itinerant-electron-mediated spin interactions. In these skyrmion-hosting materials, the extremely small skyrmions are realized and thus they are anticipated for future applications.
 In this study, we focused on a Gd-based compound with tetragonal space group I4/mmm and measured its physical properties. As a result, steep peak structures of Hall resistivity are observed in accord with the step-like anomalies of magnetization, which strongly suggests the formation of skyrmions. In this presentation, detailed spin textures realized in this compound will be discussed based on the neutron and X-ray scattering measurement results.
発表言語 日本語
発表者名 張 灵飛
指導教員名 川﨑 雅司 教授
発表題目(英語) Exploration of novel properties in perovskite Ru(III) oxides LnRuO3 stabilized by thin film fabrication
要旨(英語)  Ruthenium oxide has attracted interests because of its itinerant 4d electrons. For example, RuO2 and Sr2RuO4 are superconductors, SrRuO3 is a ferromagnet with Weyl-fermion behavior, *A*-site substitution (Ca2+, Ba2+, Pb2+) of SrRuO3 is also extensively researched to clarify a relationship between the magnetism and RuO6 distortion.
 However, although Ru may take from 2+ to 8+, most of the studies are concentrating on Ru(IV) oxides. Here, we focus on perovskite LnRuO3, which contains Ru3+ ion in B-site. Ru3+ has the same t2g5 electron configuration as Rh4+ and Ir4+ in perovskite rhodate ARhO3 and iridate AIrO3. In those t2g5 system, an unusual insulator behavior which origins from J = 1/2 ground state and a Dirac semimetal state was observed in iridates. In Ru(III) perovskite, besides the effect of t2g5 electrons, magnetic moment from Ln3+, which is absent in ARhO3 and AIrO3, may correlate with Ru3+ and therefore influence the magnetic properties. Additionally, a (111) bilayer structure of LaRuO3 on LaAlO3 substrate is theoretically predicted to be a topological metal. From these reasons, the exploration of LnRuO3 series may open a new playground for 4d perovskite materials.
 From several previous reports, high pressure (over 10GPa) is needed to synthesize most of polycrystalline bulk LnRuO3 except for LaRuO3, indicating single crystals are challenging to obtain. Therefore, properties of LnRuO3 are still unclear.
 In our study, we aim to fabricate single crystalline thin films of LnRuO3 by epitaxial stabilization using pulsed laser deposition and reveal their magnetotransport properties.
発表言語 英語

Bグループ

座長
鎌谷 拓実
指導
教員名
森本 高裕 准教授
座長
上島 卓也
指導
教員名
沙川 貴大 教授
発表者名 渡辺 柊
指導教員名 中村 泰信 教授
発表題目(英語) Implementation of ZZ-robust single-qubit gate in integrated superconducting quantum circuits
要旨(英語)  Superconducting qubits are a promising physical system for realizing quantum computers, and have been the subject of research worldwide. In fixed-frequency, fixed-coupling superconducting qubit integrated circuits, unwanted couplings to neighboring qubits called residual ZZ interactions are an obstacle to improving quantum gate fidelity. In this talk, I will describe a method for designing quantum gates that are resistant to gate errors caused by ZZ interactions by optimizing pulse waveforms, and demonstrate the effectiveness of this method through experiments using multiple superconducting qubits.
発表言語 日本語
発表者名 廉 東奇
指導教員名 長谷川 幸雄 教授
発表題目(英語) Low-temperature STM measurement of Pb atomic-layer on Si(001)2x1 surfaces
要旨(英語)  Superconducting thin films show unique characteristics because of their thickness smaller than the coherence length. One of the ultimate thin superconducting films is the mono-atomic layer superconductor formed on semiconductor substrates. For monolayer superconductors, since over-layers do not connect continuously across a step, steps can affect superconducting properties. For example, the behavior of vortices at steps are different depending on the strength of coupling of electrical states between upper and lower terraces across a step, as demonstrated on Pb monoatomic-layers on Si(111), which is known to form various superconducting phases. In the case of Si(111)- striped incommensurate -Pb phase, the step works as a pinning center for vortices because the coupling is rather strong. On the other hand, the vortices are apparently repelled by the steps on and Si(111)-√3×√43-Pb because the coupling is rather weak. However, it is still unclear what factor makes the difference in coupling of electrical states.
 Here, we focused on the different substrates, Si(001), which have different symmetry. On Si(001), it is known that the 2x1 dimer reconstructed structures are formed on the surface with the 90°rotated dimer lines across a step. This may make the difference with the influence of the steps. On the other hand, it has not been reported if Pb atomic layers formed on Si(001) show superconductivity. By analogy from the fact that more than 1.2 ML Pb on Si(111) surfaces show superconductivity, we expect that more than 1.4 ML of Pb on Si(001) substrates show superconductivity. Therefore, we studied the Si(001)-c(4x4)-Pb (1.875 ML), one of the atomic layer structures formed on Si(001) substrates, using a 3He-cooled ultrahigh vacuum low-temperature scanning tunneling microscope (STM). We found the 0.4 meV energy gap around Fermi level, which is the same order as that of common atomic layer superconductors. However, vortices are not observed due to the presence of many structural defects disturbing superconductivity.
発表言語 日本語
発表者名 楊 暁達
指導教員名 香取 秀俊 教授
発表題目(英語) Spectroscopy of 87Sr clock transition in the small-sized atom trapping system
要旨(英語)  Optical lattice clocks have realized 10^(-18) level of systematic uncertainty with about a few hours of integration time. Various usage of the clocks are expected, such as redefinition of the second, relativistic geodesy and search for new physics. Improving the clock's transportability is inevitable for wide applications. In the introduction part, I will briefly explain the fundamentals of optical lattice clocks: the principles of operation and the directions of development.
 In the apparatus part, I will explain the outline of small-sized atom trapping system: the configurations of magnetic field and laser path for laser cooling and trapping.
 In the experiment part, I will show the processes and the results achieved so far with the system under development: trapping strontium atoms in optical lattices and spectroscopy of clock transition.
 Summary and future prospects will follow in the end.
発表言語 英語