＼オープン形式で開催！どなたでも出入り自由／｜開催日時

2024.3.14(木) 13:00～17:45｜開催場所※セミナーは15:00～17:00

片平北門会館2階・エスパス

｜主催
｜共催
｜講師

UW-TU Academic Open Space (AOS)
材料科学国際共同大学院（GP-MS）
スピントロニクス国際共同大学院（GP-Spin）

Xiaodong Xu 教授
ワシントン大学材料工学科/物理学科

セミナー①15:00～16:00
分数量子異常ホール効果の観測
強い電子-電子相互作用下での分数量子異常ホール（FQAH）効果の実験的観測を報告。また、異常ホール状態の発見やその関連効果による電荷の分数化やanyon統計の研究への新たな展望について。

Di Xiao 教授
ワシントン大学材料工学科/物理学科

セミナー②16:00～17:00
ねじれ二層TMDsにおけるトポロジカル状態
零磁場での整数および分数の量子ホール効果に注目が集まる
ねじれ二層TMDsについて解説。機械学習や極化電荷の役割、さまざまな充填における相図などを議論。

全体のスケジュール：13:00-13:15 開会あいさつ等
13:15⁻13:40 東北大学の量子研究の概要（山下太郎教授）
13:40⁻14:40 研究紹介（佐藤宇史教授、好田誠教授、加藤俊顕准教授）
15:00-17:00 セミナー（Xiaodong Xu教授、Di Xiao教授）
17:10-17:40 ラウンドテーブルディスカッション｜お問い合わせ 国際企画課国際事業係： kokusai-r@grp.tohoku.ac.jp

OBSERVATION OF FRACTIONAL QUANTUM ANOMALOUS HALL EFFECT
Xiaodong Xu
xuxd@uw.edu, https://sites.google.com/uw.edu/xulab
Department of Physics, Department of Materials Science and Engineering
University of Washington, Seattle, WA
The interplay between spontaneous symmetry breaking and topology can result in exotic quantum
states of matter. A celebrated example is the quantum anomalous Hall (QAH) effect, whichexhibits an integer quantum Hall effect at zero magnetic field due to topologically nontrivial bands
and intrinsic magnetism. In the presence of strong electron-electron interactions, fractional-QAH(FQAH) effect at zero magnetic field can emerge, which is a lattice analog of fractional quantum
Hall effect without Landau level formation. In this talk, I will present experimental observation ofFQAH effect in twisted MoTe2 bilayer, using combined magneto-optical and -transportmeasurements. In addition, we find an anomalous Hall state near the filling factor -1/2, whose
behavior resembles that of the composite Fermi liquid phase in the half-filled lowest Landau levelof a two-dimensional electron gas at high magnetic field. Direct observation of the FQAH andassociated effects paves the way for researching charge fractionalization and anyonic statistics atzero magnetic field.
Reference

1. Observation of Fractionally Quantized Anomalous Hall Effect, Heonjoon Park et al., Nature,https://www.nature.com/articles/s41586-023-06536-0 (2023);
2. Signatures of Fractional Quantum Anomalous Hall States in Twisted MoTe2 Bilayer, Jiaqi Cai
et al., Nature, https://www.nature.com/articles/s41586-023-06289-w (2023);
3. Programming Correlated Magnetic States via Gate Controlled Moiré Geometry, Eric Anderson
et al., Science, https://www.science.org/doi/full/10.1126/science.adg4268 (2023).
Short Bio.
Xiaodong Xu is a Boeing Distinguished Professor in the Department of Physics, and Departmentof Materials Science and Engineering at the University of Washington. He obtained a PhD in
Physics from the University of Michigan in 2008. After postdoc research at Cornell University, hejoined the University of Washington in 2010. He is a Fellow of American Physical Society andOptical Society of America.

TOPOLOGICAL STATES IN TWISTED BILAYER TRANSITION METAL DICHALCOGENIDESDi Xiao
Department of Materials Science and Engineering, Department of Physics,
University of Washington, Seattle, WA
Recently, both the integer and fractional quantum Hall effect has been observed in twisted bilayertransition metal dichalcogenides (TMDs) at zero magnetic field, generating widespread interest in
this materials system. In this talk, I will first briefly review the route towards materials realizationof topological states, and then focus on the basic models describing twisted bilayer TMDs,including the origin of the nontrivial topology. I will then discuss how machine learning method
can be used to establish the microscopic Hamiltonian and the important role of polarization charges
in determining the band topology. Phase diagrams at various fillings as a function of twist angle
and gate voltage will be discussed as well.
Reference
1. Interface engineering of quantum Hall effects in digital transition metal oxide heterostructures,
Xiao et al, Nature Commun. 2, 596 (2011)
2. Fractional Chern insulator in twisted bilayer MoTe2, Wang et al, Phys. Rev. Lett. 132, 036501(2024)
3. Polarization-driven band topology evolution in twisted MoTe and WSe2, Zhang et al, arXiv:
2311.12776

Short Bio.
Di Xiao is the Robert J. Campbell Professor of Materials Science and Engineering, and Professorof Physics at the University of Washington. He obtained his PhD in Physics from the Universityof Texas at Austin in 2007. After a four year stint at Oak Ridge National Laboratory, he joined
Carnegie Mellon University in 2012, and moved to the University of Washington in 2021. He is aFellow of American Physical.