The link between Hundsness and superconductivity

Aalto Quantum Physics Seminars (Hybrid). Speaker: Prof. Kristjan Haule (Rutgers University)
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The numerically exact solutions of the uniform electron gas problem by variational diagrammatic Monte Carlo method at metallic densities [1,2] gave us new insights into the screening in solids and show that in metallic solids the short-range interaction point of view is most appropriate for fast convergence towards the exact solution. This gives us a new understanding of why embedding through Dynamical Mean Field Theory (DMFT) has been so successful in describing numerous correlated solids. In this talk, I will highlight a few examples of DFT+embedded DMFT functional predictions verified experimentally, including prediction of electron-phonon coupling in FeSe[3,4], strong incoherence of the normal state in Fe superconductors and its Hund's coupling origin. I will show that the Hundsness in these superconductors has huge effect on both the normal and the superconducting state properties [3-6] as well as the lattice dynamics and electron-phonon coupling.

[1] A combined variational and diagrammatic quantum Monte Carlo approach to the many-electron problem, Kun Chen and Kristjan Haule, Nature Communications, 10(1):3725, 2019.

[2] Single-particle excitations in the uniform electron gas by diagrammatic Monte Carlo, Kristjan Haule and Kun Chen, Scientific Reports, 12(1):2294, 2022.

[3] Strong pressure-dependent electron-phonon coupling in FeSe, Subhasish Mandal, R. E. Cohen, and K. Haule, Phys. Rev. B 89, 220502(R) (2014).

[4] Femtosecond electron-phonon lock-in by photoemission and x-ray free-electron laser, Gerber S, Z.X.Shen,, Science 357, 6346 (July 2017).

[5] Spin dynamics and orbital-antiphase pairing symmetry in iron-based superconductors, Z. P. Yin, K. Haule, and G. Kotliar, Nature Physics 10, 845–850 (2014).

[6] Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides, Z. P. Yin, K. Haule, G. Kotliar, Nature Materials 10, 932-935 (2011).

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