座長：大原 健悟、大森 遼
| 氏名： 青木
指導教員名： 嶽山 正二郎 教授
発表題目（英語）： Solid state physics of CuCrO2 under ultra-high magnetic fields
要旨（英語）： Triangular lattice antiferromagnets are widely studied the field of magnetism. Complex orderings (spin, lattice, and orbit) and rich phase diagrams arise because three antiferromagnetic interactions within a triangle cannot be simultaneously satisfied. In CuCrO2, Cr3+ ions s = 3/2 form the slightly deformed triangular lattice. Therefore, the geometrical frustration will induce the various magnetic phases up to the magnetic saturation phase. Magnetic field that can saturate with the magnetization of CuCrO2 is about 300T. So using destructive generation of magnetic field is only way to measure the saturated magnetization of CuCrO2. I investigated the high-field properties of CuCrO2 up to 160 T, generated by the destructive single-turn coil pulsed magnet. The magnetization is measured by magneto-optical Faraday rotation method. I found a tiny jump in magnetization with a hysteresis at 75 T, indicating the first order phase transition takes place. Above 75 T, the magnetization monotonically increases with the magnetic field. This is inconsistent with a result of Monte Carlo simulation, which predicts a robust 1/3 plateau phase above 75 T. A comparison with a different model will be discussed.
| 氏名： 石黒
指導教員名： 渡辺 悠樹 講師
発表題目（英語）： generalization of LSM-HO theorem to the φ-flux systems
要旨（英語）： There are three types of the energy structures in the many body systems, which have one of following. Gapped ground state, degenerate gapped ground state or gapless ground state.
Lieb-Shultz-Mattis (LSM) theorem claims a particular conditions to realize gapped non-degenerated ground state, where the condition is the filling of the system.
However, the original LSM theorem cannot distinguish Symmetry Protected Topological (SPT) phase from the trivial phase. For example, both the topological insulator and the trivial band insulator have a unique gapped state.
In case of the systems containing φ-flux, LSM theorem can be generalized to distinguish SPT from trivial phases by filling. In the present study, in addition to the φ-flux assumption we introduce rotational symmetry Cn. By using this we derived classification of SPT phases.
| 氏名： 足立
指導教員名： 長田 俊人 准教授
発表題目（英語）： Dimensional crossover effects of topological insulators and techniques of atomic layer stacking
要旨（英語）： In recent years, topological insulators (TI) have attracted a great deal of attention and intensively studied as a new class of quantum matters. TI has metallic surface states on the boundaries while having a bulk insulator gap. Depending on topological invariant Z2 indices, three-dimensional TIs are classified into two types: strong topological insulator (STI) in which surface states appear on all surfaces and weak topological insulator (WTI) in which the surface states appear only on specific surfaces. As a bulk of STI is made thinner, it changes to WTI or ordinary insulator. The topological phase transition accompanying dimensional crossover has not been investigated experimentally from the viewpoint of quantum transport, and we attempt to elucidate this.
Inevitably doped bulk carrier is an obstacle when trying to examine the surface states of the three-dimensional TI from transport properties. In the case of Bi2Se3, it is strongly n-doped with Se defects, and the surface states are located deep under the Fermi level. In order to remove bulk carriers, methods of solid solution, surface doping, gate tuning by FET structure, and thinning have been attempted. In this study, we will thin the bulk crystal by mechanical cleavage method, create an FET structure using techniques of atomic layer stacking, and try to observe the surface states.
| 氏名： 板橋
指導教員名： 岩佐義宏 教授
発表題目（英語）： Nonreciprocal Transport in 2D superconducting MoS2
要旨（英語）： Transition metal dichalcogenide (TMD) crystals are becoming a platform for investigating intrinsic physical properties owing to its high-crystallinity. One of the most important characteristic of two-dimensional (2D) TMDs is threefold symmetry in its single layer form. In this poster, we report the intrinsic vortex ratchet effect, i.e. vortex rectification effect, without artificial asymmetric structure.
While it has been reported that the transverse resistance depends on the current direction parallel to the armchair edge , we found that similar behavior is observed even in the Hall resistance in the current direction parallel to the zigzag edge with no signals in transverse resistance. These anisotropic behavior is explained in light of three fold symmetry, indicating the signal comes from its intrinsic crystal structure. The present results suggest that 2D superconducting TMDs with threefold symmetry have a great potential for becoming a key tool such as vortex rectifier toward future superconducting nanoelectronics.
| 氏名： 池田
指導教員名： 吉岡 孝高 准教授
発表題目（英語）： Stabilization of a Ti:Sapphire frequency comb using the optical fiber link of UT
要旨（英語）： An optical frequency comb is a laser whose spectrum consists of a series of evenly spaced longitudinal modes in the optical frequency domain realized by a highly stabilized mode-locked laser. It is utilized in various fields, mainly on high-precision optical frequency metrology, and longitudinal modes need to be accurate and stabilized for high-precision metrology. Longitudinal modes are locked to external references, such as a RF frequency standard and a laser having extremely precise frequency, and accuracy and stability of a frequency comb depend on those of the external references. Today, researches on an optical frequency standard have been developed and optical atomic clocks having stability beyond the Cs atomic clock are realized. It is expected that the redefinition of a second by an optical frequency standard such as an optical lattice clock will be done in the near future. Therefore, the development of next generation precision spectroscopic technology utilizing an optical clock is required. We have developed an ultra precise optical frequency comb locked to a laser for a Sr optical lattice clock in Katori Laboratory. First, an optical frequency comb was made from a mode-locked Ti:Sapphire laser whose spectrum can be easily expanded to a broad wavelength range including ultraviolet. To stabilize the optical frequency comb, a clock laser, whose frequency is extremely stabilized, was transmitted from Katori Laboratory to our laboratory through the optical fiber link of UT. To compensate phase noises arising in optical fibers, a technique called “fiber noise cancelling” was done. Finally, using the transmitted clock laser as a reference, the longitudinal modes of the frequency comb were locked. In this presentation, I will explain the detailed techniques and the results.
| 氏名： 井出 元
指導教員名： 川﨑 雅司 教授
発表題目（英語）： Growth and transport properties of superconducting Sr2RuO4 thin films
要旨（英語）： BCS theory is known as a fundamental theory of describing superconducting phenomena. This theory meets well for spin-singlet s-wave superconductors. On the other hand, there are other types of superconducting materials like high-Tc cuprates, and it is impossible to explain other types of superconducting phenomenon.
Sr2RuO4 is one of the materials which is not included within the BCS theory. Its superconducting symmetry is categorized to spin-triplet, especially two-dimensional chiral p-wave superconductor, classified into a topological superconductor.
We have worked on fabrications of high quality Sr2RuO4 superconducting thin films and its Josephson devices. In this talk, first, I will explain the Sr2RuO4’s characteristic superconducting states comparing to s-wave superconductors. Next, I will explain the importance and difficulty of fabricating Sr2RuO4 in the state of thin films. Finally, I will talk about the details of the growth of Sr2RuO4 thin films and its transport properties.