応用物理学輪講 I
11月19日
[注意事項]
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発表日
2021年11月19日(金)16:50〜

Aグループ

座長
西澤 葉
指導
教員名
賀川 史敬 准教授
座長
花村 文哉
指導
教員名
古澤 明 教授
発表者名 長吉 博成
指導教員名 古澤 明 教授
発表題目(英語) Programmable platform for optical Measurement-Based Quantum Computation
要旨(英語)  Measurement-Based Quantum Computation (MBQC) is a computational model that focuses on the effect of quantum measurement. This model is promising for realizing a continuous-variable optical quantum information processing. Particularly, we are engaged in a project to demonstrate experimental method to utilize a massive entangled state called cluster state in MBQC. In principle, universal quantum computation is accomplished by only applying a sequence of proper projective measurements onto the cluster state. Nevertheless, the actual framework for programmable MBQC that converts program codes into efficient measurement sequences on the cluster state has been scarcely investigated. Here we propose a primitive programming language scheme inspired by the conventional functional programming and how one can obtain desired measurement procedures based on it. Moreover, we also examine the compatibility of this programming language with a flexible MBQC protocol and the possible formulation of circuit optimization as an allocation problem.
発表言語 英語
発表者名 沼田 淳希
指導教員名 齊藤 英治 教授
発表題目(英語) Spin-orbit torque in a broken inversion symmetry system
要旨(英語)  Spintronics is the research field that utilizes both the charge and spin degrees of freedom of electrons. One of the hottest topics in the field is the spin-orbit torque (SOT), referring to magnetic torque acting on spins due to effective fields induced by spin-orbit interaction. In particular, in magnetic conductors with broken inversion symmetry, the SOT can be driven simply by applying a charge current and detected as an electric voltage via ferromagnetic resonance, through which rich information on the nature of spin-orbit interaction is obtained.
 In this presentation, I will talk about SOT in NiMnSb thin films epitaxially grown on GaAs. NiMnSb is a noncentrosymmetric magnetic conductor having a high Curie temperature of 730 K, and its epitaxial film has shown to exhibit moderate Rashba and Dresselhaus spin-orbit interactions. The SOT in this material has been reported at room temperature, but at low-temperatures a new aspect on SOT may appear reflecting the exotic spin excitations, which I will discuss during the talk.
発表言語 日本語
発表者名 野原 大和
指導教員名 中野 匡規 特任准教授
発表題目(英語) Nonreciprocal transport in MoTe2
要旨(英語)  I focus on transition metal dichalcogenide (TMD) with broken inversion symmetry, and investigate 2nd order nonlinear transport which is the characteristic phenomena reflecting the broken symmetry.
Target material is MoTe2. In Mote2, the polar structure appears at low temperatures due to the temperature-dependent stacking behavior.
In this study, nonreciprocal transport was observed in the orientation perpendicular to the magnetic field and polarity. In addition, by measuring the temperature dependence, it was found that the nonreciprocal transport was enhanced as the hole carrier density increased at low temperature.
Such a behavior has never been observed before in Rashba systems.
Therefore, this suggests the possibility that the nonreciprocal transport originating from a new mechanism unique to the electronic structure of MoTe2 is realized in this material.
発表言語 日本語

Bグループ

座長
中津 裕貴
指導
教員名
福谷 克之 教授
座長
二階堂 圭
指導
教員名
長谷川 達生 教授
発表者名 畑中 樹人
指導教員名 有田 亮太郎 教授
発表題目(英語) First Principles Study on the magnetic structure of TMDs with transition metal intercalations
要旨(英語)  Recently, various interesting properties have been observed by inserting metallic elements between the layers of transition metal dichalcogenides (TMDs), which are layered materials, and have been intensively studied. The various magnetic properties observed are of practical importance, as they have been suggested to be applied to spintronics devices. Although there have been many studies of experimentally synthesized individual materials, no systematic studies which include those that have not been synthesized have been performed.
 In my research, I performed first-principles calculations on a total of 96 materials with different composition ratios and intercalated transition metals, and investigated their magnetic properties. The results were used to calculate the energy dependence of the exchange constants by downfolding results into a tight binding model. In this presentation, in addition to the analytical method and the results, we will discuss the future prospects.
発表言語 日本語
発表者名 畠村 匠
指導教員名 鹿野田 一司 教授
発表題目(英語) NMR study of Dirac nodal line materials [Ni(dmdt)2].
要旨(英語)  The electron system in which electrons behave as if they have zero effective mass is called “Massless Dirac Fermions” (MDF), and is characterized by very high mobility and a special Landau level. A single molecular conductor [Ni(dmdt)2] is known as MDF, and first-principles calculations have shown that Dirac nodal line, where Dirac points of linear dispersion are distributed linearly in a 3D Brillouin zone, appears in it. Although the magnetic susceptibility has been measured in previous studies, no experiments have yet been conducted to observe the electronic state microscopically.
 In this presentation, I will present the results of 13C NMR experiments on polycrystalline samples of 13C substituted [Ni(dmdt)2]. Then, I will explain the electronic structure of [Ni(dmdt)2] based on the measured spectral shifts and the nuclear spin-lattice relaxation rate 1/.T.1. Finally, a summary and future perspectives will be given.
発表言語 日本語
発表者名 馬場 智大
指導教員名 鹿野田 一司 教授
発表題目(英語) Seebeck effect under pressure in the neutral-ionic transition material TTF-CA
要旨(英語)  The quasiーone-dimensional donor-acceptor mixed-stack complex tetrathiafulvalene-p-chloranil (TTF-CA) is a strongly coupled charge-spin-lattice system, which undergoes the neutral-ionic transition depending on the pressure and temperature. At ambient pressure, TTF-CA is in the neutral phase at room temperature, and exhibits a charge-transfer transition at 81 K, accompanied by a lattice dimerization due to the spin-Peierls mechanism. The charge transfer is decoupled from the lattice dimerization with applied pressure, and the non-dimerized ionic phase emerges in the high pressure and temperature region. In recent years, it has been experimentally shown that electrical conduction and magnetism at high temperature above the dimerization temperature TC are carried by the topological excitations, such as the neutral-ionic domain walls emerging between the neutral and the ionic domains, and the solitons which are left out of dimers [1,2]. These topological excitations are expected to provoke a novel thermoelectric effect. In the present study, we measured the Seebeck coefficient under various pressure and temperature to elucidate the mechanism of thermoelectric effect carried by the topological excitations.
 We found that the Seebeck coefficient is positive in the neutral phase and negative in the ionic phase, indicating that the mobility of carriers with positive charge is larger than that with negative one in the neutral phase, and vice versa in the ionic phase. In addition, the energy gap, estimated from the formula of Seebeck coefficient which holds for semiconductors, is close to the gap evaluated from the electrical conductivity below Tc, whereas those two gaps are quite different above Tc, where the topological excitations are dominant. This difference suggests that the thermoelectric effect above Tc cannot be explained by the simple semiconductor picture due to the emergence of topological excitations.

[1] K. Sunami, et al., Sci. Adv. 4, eaau7725 (2018).
[2] R. Takehara, et al., Sci. Adv. 5, eaax8720 (2019).
発表言語 日本語