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Strong Correlation and Unconventional Superconductivity in Bulk and Trilayer Alkali-Doped Fullerides

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The alkali-doped fullerides A3C60 (A = K, Rb, Cs) exhibit strong correlation and unconventional superconductivity (SC) in both bulk and thin films. In the first part of the seminar [1], the speaker will investigate the unconventional pairing mechanism in bulk A3C60 using dynamical mean-field theory (DMFT) in the Nambu formalism. He will show that the local orbital fluctuations are substantially enhanced in the superconducting state and provide the pairing glue in A3C60 . A lock-in phenomenon between the SC gap (fermionic) and the local orbital fluctuation energy (bosonic) is found, which is consistent with an experimentally observed universal linear relationship.

Epitaxially grown K3+xC60 thin films exhibit a Mott insulating state in the monolayer and a strong electron-hole doping asymmetry in the superconducting state in the trilayer [2], which asymmetry is absent in the three-dimensional bulk limit. In the second part of the seminar [3], using DFT +DMFT, the speaker will show that this doping asymmetry results from a substantial charge reshuffling from the top layer to the middle layer. The interlayer charge transfer and layer-selective metal-insulator transition result from the interplay between crystal field splittings, strong Coulomb interactions, and an effectively negative Hund coupling.

If time is allowed, the speaker would like to report our recent progress in the analytic continuation of anomalous self-energy and its application in K3C60 , which paves the way for the theoretical study of momentum resolved spectra in the SC phase using quantum Monte-Carlo method [4].

[1] C. Yue, S. Hoshino, A. Koga and P. Werner, Phys. Rev. B 104 , 075107 (2021)

[2] Ming-qiang Ren, et. al., Phys. Rev. Lett. 124, 187001 (2020)

[3] C. Yue, Y. Nomura, and P. Werner, Phys. Rev. Lett. 129, 066403 (2022)

[4] C. Yue. And P. Werner, arXiv: 2303.16888 (2023)

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