中国科学院大学卡弗里理论科学研究所

报告摘要：

Strange metals are ubiquitously observed in a variety of strongly correlated materials, among which high temperature cuprates, ruthenate oxides, and twisted bilayer graphene are the most prominent examples. In these materials, the critical quantum fluctuations are often accompanied by the Lifshitz transition of the Fermi surface where the Fermi surface exhibits van Hove singularity (VHS) and its geometry changes from convex to concave. In this talk, we address the nature of such an extreme correlated matter when both the VHS and wild quantum critical fluctuations are entangled. We adopt the Yukawa-SYK model with a spatially uniform Yukawa interaction and self-consistently solve for the low-energy effect theory which yields non-Fermi liquid states at distinct energy scales. Furthermore, we clarify the electron scattering mechanism at the Lifshitz transition and evaluate the optical conductivity and dc-resistivity by means of diagrammatic expansion. We demonstrate a linear-in-ω optical conductivity at T=0 and, more importantly, the strange metal behavior with a linear-in-T dc-resistivity in the entire quantum critical regime extending down to T→0. At higher temperatures, it eventually gives in to a non-universal scaling. In addition, we also consider the spatially random Yukawa interaction which gives rise to linear-in-T resistivity extending even into the non-universal high-T regime. Finally, we argue that our theoretical scheme for the strange metal is free from the severe short-circuit issue.

If time allows, we will briefly mention another line of development which forges an emerging interdisciplinary field between spintronics and strongly correlated matters. To set an example, we study the spin pumping effect without well-defined quasiparticles.

References:

1. Yi-Hui Xing, W. Liu, and Xiao-Tian Zhang†, Nat. Commun. under review (2025);

2. Xiao-Tian Zhang† and Yi-Hui Xing et al., Commun. Phys. 8 103 (2025).

报告人简介:

Xiao-Tian Zhang earned his bachelor’s degree from the College for Gifted Youngs at the University of Science and Technology of China in 2013. He then pursued his PhD at the International Center for Quantum Materials, Peking University, under the supervision of Prof. Ryuichi Shindou, graduating in 2019. From 2019 to 2022, he worked as a postdoc in Prof. Gang Chen’s group at the University of Hong Kong. In 2022, he joined the Kavli Institute for Theoretical Sciences as a Postdoctoral Fellow in collaboration with Prof. Fu-Chun Zhang and Special Research Assistant of UCAS (a.k.a. Assistant Researcher).

邀请人：孙培杰 研究员

联系人：王慧颖 why@iphy.ac.cn

报告地点：怀柔园区X1南楼101会议室

腾讯会议：226-676-255

会议密码：2025

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