応用物理学輪講 I
6月28日
[注意事項]
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
2024年6月28日（金）16：50～18：50

Aグループ

座長
姜　大模
指導
教員名
森本　高裕　准教授
発表者名 永濱　壮真
指導教員名 十倉　好紀　卓越教授
発表題目（英語） Topological materials and superconductors
要旨（英語） Topology is a pure mathematical concept to classify manifolds. However, this concept can also be applied to the condensed matter physics, and by using that, we can classify materials in topological ways.
There are a lot of topological materials and among them are topological superconductors. Although its existence is predicted a decade ago, understanding of its properties and its experimental observation are still in its infancy.
In this presentation, I will explain some of topological materials including topological superconductors, and then show you what I’m currently working on.
発表言語 日本語
発表者名 中田　勇宇
指導教員名 木村　隆志　准教授
発表題目（英語） Towards stimulated resonant inelastic X-ray scattering imaging using an X-ray free-electron laser
要旨（英語） Resonant inelastic X-ray scattering (RIXS) is a widely used spectroscopic technique for analyzing elementary excitations. The application of RIXS to imaging would allow for more detailed analysis of inhomogeneous materials. However, RIXS imaging is challenging because the extremely low scattering cross-section makes scanning X-ray microscopy difficult at conventional synchrotron X-ray facilities.

To overcome the low efficiency of RIXS, we propose to stimulate the RIXS process (SRIXS) with a soft X-ray free-electron laser (SXFEL), increasing the photon yield by up to 6 orders of magnitude. The stimulated process requires two-color X-rays for the excitation (pump) and stimulated emission (Stokes) steps. To focus both colors to high intensity, we plan to manufacture a new achromatic full-field twin Wolter mirror microscope capable of sub-micron focusing and large magnification. The resulting image will be spectrally dispersed at many spatial points using a multi-aperture grating (MAG) currently in development, enabling hyperspectral imaging with a sub-beam size spatial resolution and a sub-eV spectral resolution.

This presentation will show results of simulations using a three-level Maxwell-Bloch model to estimate the SRIXS signal strength given the beam parameters of the SACLA BL1 SXFEL. The design of the Wolter mirror optics and MAG are then discussed in accordance with the simulation results.
発表言語 日本語
発表者名 畠中　友也
指導教員名 森本　高裕　准教授
発表題目（英語） Dynamically Generated Logical Qubits
要旨（英語） Quantum error correction is essential for achieving error-free quantum computation. A simpler example is the Toric code (surface code), which defines a local stabilizer code on a two-dimensional surface. Unlike stabilizer codes such as the Toric code, which are mutually commuting, there are subsystem codes that are non-commuting. These codes increase the number of measurement operators but reduce the number of qubits used for measurement. Recently, a time-driven Floquet code (or honeycomb code) has been proposed as a type of subsystem code that does not have logical qubits but, through periodic measurements, has logical qubits that change over time, allowing for error correction. This review will discuss the Floquet code and compare it with other codes.
発表言語 英語

Bグループ

座長
BAEK　Gwangil
指導
教員名
平山　元昭　特任准教授
発表者名 中野　遼太
指導教員名 Max　Hirschberger　准教授
発表題目（英語） Anisotropic electrons in a short period helimagnet
要旨（英語） The mutual conversion between heat and charge (thermoelectric effect), represented by the Seebeck effect and the Peltier effect, is an extremely important concept from the perspective of energy harvesting. In particular, the Peltier effect, in which an electric current induces a heat flow, can be used to cool the junction surface of p-type and n-type semiconductors. Recently, by focusing on the anisotropy of the thermoelectric effect in ferromagnetic materials, Peltier cooling has been realized in a single material without a junction [1]. On the other hand, cooling devices based on ferromagnetic materials have problems such as small anisotropic thermoelectric response and complex device structures. In this presentation, we propose a novel local cooling technique using anisotropy generated by the magnetic propagation vector Q of helimagnet. We will discuss it together with the data of the target Gd-based intermetallic compound.
[1] K. Uchida et al., Nature (2018)
発表言語 英語
発表者名 服部　航平
指導教員名 有田　亮太郎　教授
発表題目（英語） Effect of collective spin excitation on electronic transport in topological spin texture
要旨（英語） We develop an efficient real-time simulation method for the spin-charge coupled system in the velocity gauge.
This method enables us to compute the real-time simulation for the two-dimensional system with the complex spin texture.
We focus on the effect of the collective excitation of the localized spins on the electronic transport properties of the non-trivial topological state in real space.
To investigate this effect, we calculate the linear optical conductivity by calculating the real-time evolution of the Kondo lattice model on the triangular lattice, which hosts an all-in/all-out magnetic structure.
In the linear conductivity spectra, we observe multiple peaks below the bandgap regime, attributed to the resonant contributions of collective modes similar to the skyrmionic system, alongside broadband modifications resulting from off-resonant spin dynamics.
The result shows that the collective excitation, similar to the skyrmionic system, influences the optical response of the electron systems based on symmetry analysis.
We elucidate the interference between the contributions from the different spin excitations to the optical conductivity in the multiple spin texture, pointing out the mode-dependent electrical activity.
We show the complex interplay between the complex spin texture and the itinerant electrons in the two-dimensional spin-charge coupled system.
発表言語 英語
発表者名 花田　達希
指導教員名 平山　元昭　特任准教授
発表題目（英語） Topological phase transition hidden in metal-semimetal transition of Sn
要旨（英語） α-Sn, a zero-gap semiconductor, exhibits unique topological characteristics. Conversely, the metastable trivial metal phase, β-Sn, emerges thorough compression of α-Sn along the (001) direction, showcasing superconductivity. These phases differ in chemical bond properties and topological features, raising the question of a topological phase transition during the structural shift between α-Sn and β-Sn. In this investigation, we delve into the structural phase transition from the aspect of topological physics to elucidate the origin of metastability. Our study presents the phase transition pathway between α-Sn and β-Sn, along with electronic structure changes calculated using the nudged-elastic-band (NEB) method, GW approximation, and crystal orbital bond index (COBI) analysis. In the presentation, we will discuss the application of the metastability between metal phase and nonmetal phase.
発表言語 日本語
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