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Title: Strange metal at Lifshitz transition
Speaker: Xiao-Tian Zhang 张啸天
Affiliation: Kavli Institute for Theoretical Sciences, UCAS
†Email: zhangxiaotian@ucas.ac.cn
Abstract:
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[1], 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 due to the presence of boson thermal mass[2]. 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 encountered near antiferromagnetic quantum criticality. If time allows, we will briefly mention the ongoing studies on competition between non-Fermi liquid and superconductivity near a VHS.
About the speaker:
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 Department of Physics, 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 Assistant Researcher of UCAS.