Theoretical explorations on unconventional superconductivity: phenomenological & model studies

报告人

Dr. Yu Li (李宇)

Kavli Institute for Theoretical Sciences, 

University of Chinese Academy of Sciences

时间

2023年3月27日（星期一）上午10：00

地点

物质科学教研楼B902会议室

Yu Li, graduated from the Donghua University in 2012, and got the PhD from the Institute of Physics, Chinese Academy of Sciences in 2018. From 2019 to now, he works as a postdoctoral in Kavli Institute for Theoretical Sciences, University of Chinese Academy of Sciences (KITS, UCAS). His research interests mainly focused on the pairing mechanism on unconventional superconductivity (SC), such as: pairing symmetries in heavy-fermion SCs, Kerr effect in chiral SCs, and the exploration of the novel properties in the models of non-Fermi-liquid SC.

报告摘要

In many phase diagrams of unconventional superconductors (such as heavy fermions, cuprates, and iron-pnictides, etc.), superconductivity usually emerges out near the border of the magnetic ordering and involves a non-Fermi liquid normal state. My talk will show our studies from the spin-fluctuation approach and the non-Fermi liquid approach, separately. In the first part, based on the spin-fluctuation mechanism, I will introduce our phenomenological calculations to the typical heavy-fermion superconductors CeCu₂Si₂ [1], YbRh₂Si₂ [2], etc. [3]. In CeCu₂Si₂, our calculations first predict a (nodeless) s^±-wave pairing, which providing a new angle to understand the debated pairing symmetry in superconducting CeCu₂Si₂ on experiments. And in YbRh₂Si₂, a nearly degenerate d_x2-y2 and (p_x+ip_y) wave pairing is predicted, which can provide a reference to understand the observed two-SC phases in YbRh₂Si₂ recently. In the second part, we start from the exactly-solvable Hatsugai-Kohmoto model [4], which shows an unconventional metallic state beyond the Landau’s paradigm and the Green’s function has the similar form as the Yang-Rice-Zhang’s ansatz for cuprates. With the on-site Hubbard interaction in momentum space, we introduce an emergent “two-band” description, and show how the Cooper instability on the “two-Fermi surfaces” occur simultaneously. Under the attractive pairing interaction, our calculation shows a novel ”two-stage” superconductivity, which may provide a new hint to approach the strongly-correlated superconductivity in theory. And if time permits, in the final part of the talk, I will briefly introduce our two proposals to understand the Kerr effect in chiral superconductivity [5,6].

[Reference]:

[1] Y. Li, M. Liu, Z. Fu, X. Chen, F. Yang, Y.-F. Yang, Phys. Rev. Lett. 120, 217001 (2018).

[2] Y. Li, Q. Wang, Y. Xu, W. Xie, Y.-F. Yang, Phys. Rev. B 100, 085132 (2019).

[3] 李宇,盛玉韬,杨义峰, 物理学报 70, 017402 (2021).

[4] Y. Li, V. Mishra, Y. Zhou, F.-C. Zhang, New J. Phys. 24, 103019 (2022).

[5] Y. Li, Z. Wang, W. Huang, Phys. Rev. Research 2, 042027(R) (2020).

[6] J.-L. Zhang, Y. Li, W. Huang, F.-C. Zhang, Phys. Rev. B 102, 180509(R) (2020).