Abstract:

　　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).

Introduction:

　　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.