応用物理学輪講 I
5月21日
[注意事項]
発表の10日前までに宛てに「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5月11日(火)14:55〜16:55

Aグループ

座長
松前 拓実
指導
教員名
為ヶ井 強 准教授
座長
松山 直史
指導
教員名
小濱 芳允 准教授
発表者名 天野 元揮
指導教員名 求 幸年 教授
発表題目(英語) Concavity in quantum heat engines with effective negative-temperature heat bath
要旨(英語) Quantum thermodynamics is a research field that bridges thermodynamics and quantum mechanics. For example, this field includes studies of the second law of thermodynamics in quantum systems and quantum heat engines.
Recently, a new criterion of the second law of thermodynamics is proposed, which is called concavity [1]. An energy eigenstate that meets the criterion indeed obeys the principle of maximum work for adiabatic processes, which is an expression of the second law. The concavity also can be used to judge whether a mixed state obeys the second law or not and would be useful to study quantum heat engines.
 In quantum heat engines [2], there are several examples that show higher efficiency than the Carnot efficiency [3]. However, the reason why these quantum engines show high efficiency has not been clarified yet.
In this presentation, I will introduce the concept of concavity for a single energy eigenstate and a mixed state, and show a numerical estimate of the efficiency of a single qubit heat engine.
[1] C. Itoi and M. Amano, J. Phys. Soc. Jpn. 89, 104001 (2020)
[2] J. Goold et al., J. Phys. A: Math. Theor. 49 143001 (2016)
[3] J. Roßnagel et al., PRL 112, 030602 (2014)
発表言語 日本語
発表者名 伊藤 宏陽
指導教員名 川﨑 雅司 教授
発表題目(英語) Synthesis of thin films of pyrochlore oxide with possible flat band structure by pulsed laser deposition method.
要旨(英語) Flat band structure is one of the strongly correlated electron systems, which leads to some unusual physical properties such as emergence of ferromagnetism without magnetic elements. In spite of such fascinating properties, only theoretical studies have been reported have been reported due to the lack of actual materials possessing the flat band structure. However, since the first experimental realization in a twisted bilayer graphene in 2018, materials with the flat band structure have been of great interest in the field of condensed matter physics.
 Here, we focus on pyrochlore oxides (A2B2O7) which are theoretically predicted to be another candidate of the host of flat band structure. Among them, Sn2Nb2O7 and Sn2Ta2O7 are specifically expected to be promising compounds according to some first principle calculations. We aim to synthesize high-quality single crystalline thin films of them by pulsed laser deposition method in order to materialize the flat band structure.
 In this presentation, I will explain why ferromagnetism emerges in the flat band system, and why pyrochlore oxides can be candidates of it.
 Besides, I will introduce my experimental results of synthesizing and evaluating thin films of these pyrochlore oxides and discuss difficulties in inducing ferromagnetism in them.
発表言語 日本語
発表者名 海老原 豪
指導教員名 吉岡 孝高 准教授
発表題目(英語) Progress and Prospects of Ultra-low Temperature Research for Realization of BEC in Cuprous Oxide Excitons
要旨(英語) Excitons are hydrogen-like bound states consisting of electrons and holes, which are generated by photoexcitation in semiconductors. In order to realize Bose-Einstein condensation(BEC) in excitons, various techniques have been developed for cooling down to liquid He temperature. The development of ultra-low temperature technology will allow direct observation of BEC and make it possible to clarify the details of exciton BEC. As an example of such research, we will introduce our research plan to explain the dynamics of ortho-para conversion in the exciton 1s state.
発表言語 日本語

Bグループ

座長
宮田 稜
指導
教員名
長谷川 達生 教授・中嶋
座長
武藏 摩紀
指導
教員名
中野 匡規 特任准教授
発表者名 石塚 悠也
指導教員名 小林 洋平 教授
発表題目(英語) Mid-infrared spectroscopy system in the 8-12 um band
要旨(英語) The mid-infrared region has many absorption lines derived from molecular vibrations, and various spectroscopic methods are studied for applications in various fields such as breath diagnosis and fuel analysis. Especially in breath diagnosis, a high-speed, high-resolution and high-band mid-infrared spectroscopic system is required to identify multiple molecular species instantly.
 We have constructed a mid-infrared spectroscopy system using a mid-infrared comb and an extremely-high-order dispersion element and a two-dimensional array type detector. Our laboratory has constructed highly sensitive, high-resolution and real-time mid-infrared spectroscopic system in the 3-5 um band. The 3-5 um band has sharp absorption lines of light molecules, and a high-resolution spectroscopic system is required. On the other hand, the 8-12 um band has wide and complex absorption lines of heavy molecules such as aromatic compounds. So wider spectral system is required in the 8-12 um band.
 In this presentation, I will introduce the setup of mid-infrared spectroscopy system in the 8-12 um band .
発表言語 日本語
発表者名 上野 祥広
指導教員名 鹿野田 一司 教授
発表題目(英語) NMR study of doped spin liquid material κ-(ET)4Hg2.89Br8
要旨(英語) κ-(ET)4Hg2.89Br8 is a layered material, in which conducting ET layers and insulating Hg2.89Br8 layers are alternately stacked. Due to incommensurability between the ET and Hg sublattices, the ET layer with a half-filled band is 11% hole-doped and is metallic. In the conduction layer, the ET molecules form dimers, which constitute a triangular lattice. Since the spin susceptibility of κ-(ET)4Hg2.89Br8 is similar to that of the spin-liquid Mott insulator, κ-(ET)2Cu2(CN)3, with a triangular lattice, κ-(ET)4Hg2.89Br8 is considered to be a "doped spin liquid" in which the spin degree of freedom is in a spin-liquid state even though it is a metal.  In the present study, I have performed 13C NMR measurements to investigate the magnetism of this material in detail and obtained the following results.
 First, I confirmed that the NMR spectral shift (Knight shift), which measures the magnitude of the local magnetic field created by the electron spins, is scaled to the spin susceptibility and found that the spectrum is widened with decreasing temperature, suggesting an increasing inhomogeneity of the local spin susceptibility upon cooling.
 Second, the nuclear spin-lattice relaxation rate 1/T1, which measures the intensity of electron spin fluctuations, showed a temperature dependence similar to in the spin-liquid compound κ-(ET)2Cu2(CN)3. A previous study found both materials to behave similar in spin susceptibility; thus, κ-(ET)4Hg2.89Br8 is regarded as a doped spin liquid hosting both mobile carriers and a quantum spin liquid.
 Furthermore, a decreases in the Knight shift and a cubic temperature dependence of 1/T1 below 10 K suggest that superconductivity emerging in this material has spin-singlet d-wave symmetry with highly enhanced fluctuations above Tc.
発表言語 日本語