座長：杉本 宜陽、角崎 正典
|氏名： 小山 奏汰
指導教員名： 長谷川 達生 教授
発表題目（英語）： Crystal structure prediction of layered organic semiconductors based on symmetry
要旨（英語）： Although the greatest advantage of organic semiconductors is the flexibility of molecular design, the quality of their properties can only be determined by knowing the arrangement of molecules, or their crystal structure. For example, if a layered herringbone structure, which is said to be suitable for TFT structures, can be predicted at the molecular design stage, the development of new organic semiconductors can be made more efficient. However, it is difficult to predict the crystal structure of molecular materials because of the myriad of candidate structures in the vast parameter space, although many attempts have been made to search for energetically stable structures. Based on the empirical assumption that only structures with relatively high symmetry can be realized at room temperature among the innumerable candidate structures that are stable below absolute zero, we believe that a stepwise method to predict the crystal structure of polyacene semiconductors under the two assumptions of symmetry and stratification is effective. In this study, we report the results of similar attempts to apply the same approach to pentacene and anthracene, which are typical organic semiconductors with at least three polymorphs and a smaller number of fused rings, respectively. In the case of pentacene, we have succeeded in reproducing the actual crystal structure of pentacene by clarifying the mechanism of the structural polymorphism through a stepwise structure search. On the other hand, for anthracene, the molecular long axis is shorter than that of pentacene, and the parallelism of the long axis between neighboring molecules is expected to be broken, so that the prediction of the structure with the introduction of the torsion of the long axis can be extended to the system with slightly broken stratification.
|氏名： 阪本 天志
指導教員名： 吉岡 孝高 准教授
発表題目（英語）： Laser cooling of atoms using frequency comb
要旨（英語）： Laser cooling and trapping of atoms at very low temperatures are techniques of great value in a wide range of applications, such as high-precision measurements, quantum information, and chemical reaction studies.
However, traditional cooling methods with a single-frequency laser can be applied only to limited atomic species, such as alkali and alkali-earth metals which have convenient energy levels suited to current laser technology.
In particular, many atomic species of chemical and biological interest, including carbon and hydrogen, are currently out of reach due to the lack of sufficiently powerful single-frequency lasers in deep ultraviolet which are required for cooling.
In this presentation, I will introduce a new method of cooling with a frequency comb to realize laser cooling of these atomic species.
|氏名： 財津 英明
指導教員名： 岩佐 義宏 教授
発表題目（英語）： Gate-induced superconductivity and its phase diagram
要旨（英語）： The BCS・BEC limit, which is the limit of quantum condensation of the fermionic gas, has recently attracted much attention for its crossover region. In a previous study, LixZrNCl was proposed as a material that can reach the BEC limit by passing through this crossover region. The high transition temperature and the increase of the crossover temperature in the low-carrier region are advantageous to this fact.
In this study, we focus on a semiconductor, as a candidate material to reach the BCS-BEC crossover region. Because it has a simpler crystal and band structure than ZrNCl, if it is possible to reach the BCS-BEC crossover region with this material, it should be possible to obtain a hint of universal mechanism. Previous studies were limited to polycrystalline ones and no carrier density dependence was reported.
Based on this background, we have designed a gate-induced device that, for the first time, induces superconductivity in a single crystal of the material and shows that, like LixZrNCl, the transition temperature increases in the low-carrier region. This result is non-trivial and suggests that this material has a phase diagram suitable for studying the BCS-BEC crossover.
In addition, we have evaluated the anisotropy of superconductivity in this material, which is the first time to be achieved with single crystal, and its properties as an unconventional superconductor and its relation to the BCS-BEC crossover will also be of interest.
|氏名： 澤田 太郎
指導教員名： 沙川 貴大 准教授
発表題目（英語）： Several anomalous phenomena derived from exceptional points
要旨（英語）： In these days, the physics of non-hermitian systems attracts much attention. Because it is revealed that unusual phenomena which cannot be observed in hermitian systems can appear in non-hermitian systems. In particular, new band structure called "exceptional point" which emerges in non-hermitian systems predicts singular, that is divergent behavior of characteristic quantity. Non-hermitian nature of physical systems typically originates from non-equilibrium property such as gain-loss structure.
In this presentation, I am going to quickly introduce the concept of exceptional point, and review the known phenomena such as "enhanced sensitivity" and "unidirectional invisibility". And then, I will remark theoretical observations which suggests that these singular behavior can generalize and become much more radical by means of "simultaneous exceptional point" band structure. If possible, I will show the numerical results related to the above generalized phenomena to be more concrete.
|氏名： 清水 龍之介
指導教員名： 岩佐 義宏 教授
発表題目（英語）： Interfacial effect by 2D magnets in van der waals heterostructures
要旨（英語）： Two-dimensional van der Waals crystals and van der Waals heterostructures are characteristic material platforms of unique functionalities and novel physics. The recent emergence of 2D van der Waals magnets opens new possibilities for exploring new exotic physical phenomena and application for spintronics. For example, emergent phenomena have been observed in heterostructures formed by monolayer WSe2 and magnetic insulator CrI3.
To further study exotic physical properties originated from van der Waals heterostructures using 2D magnets, we designed heterostructures formed by CrI3/CrBr3. Photoluminescence probing of magnetism in these systems are presented. I will also discuss the future experiment about the van der Waals heterostructure formed by WSe2/CrBr3.
|氏名： 清水 祐樹
指導教員名： 齊藤 英治 教授
発表題目（英語）： Simulation of the dynamics of parametric excitation using the quantum Langevin equation
要旨（英語）： Parametric excitation has been actively studied in quantum optics, including squeezing of light and generation of entanglement. In magnon, Parametric excitation that has the same shape of Hamiltonian also has been studied. However, for reasons including the difficulty of the experiment, there is not as much debate about parametric excitation as there is in
In quantum optics, the dynamics of this phenomenon have been simulated, using the quantum Langevin equation. However, this method limits the domain of dynamics to real number. For this reason, simulation of magnon dynamics of parametric excitation is not enough.
In this research, by using the quantum Langevin equation extended to complex numbers, it has become possible to compute the time evolution from various initial distributions with parametric excitation. As a result, it is found that the dynamics of the parametric excitation is significantly changed when the parameter region and initial distribution are changed via
the quantum state.
|氏名： 住谷 大志
指導教員名： 小林 洋平 教授
発表題目（英語）： The development of laser in glass using direct laser writing
要旨（英語）： The femtosecond laser plays an important role in the industry of micromachining, for its ability to produce minuscule structure with smooth morphology. Recently, its usage had been limited to simple processing methods such as drilling and cutting, but complex processing methods that add functionality to materials such as superhydrophobic surfaces and waveguides are now attracting attention.
“Direct laser writing”, the technology which makes waveguides by giving refractive index change to transparent materials like glass, is one of these complex methods. This method can help produce micro optical circuits of arbitrary structure, more easily than any other method. Applying this method to gain media doped glass, one can even build a compact laser. However, this technology is still in development, because it is difficult to accurately predict refractive index change from processing parameters and material properties, and is laborious to search the vast parameter space for the optimal condition that can generate the desired refractive index
In this presentation, I will discuss my plans on developing a laser based on laser-induced waveguides, and introduce the processing and measurement system under construction.