»ã±¨±êÌâ (Title)£ºHow to predict the critical temperature of superconductors: an ab-initio perspective (»ùÓÚµÚÒ»ÐÔµÀÀíµÄ³¬µ¼ÁÙ½çζÈÔ¤²â)

»ã±¨ÈË (Speaker)£ºE. K. U. Gross (Fritz-Haber Center for Molecular Dynamics, The Hebrew University of Jerusalem)

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A prominent challenge of modern condensed-matter theory is to predict material-specific properties of superconductors, such as thecritical temperature. The traditional model of Bardeen, Cooper and Schrieffer (BCS) properly describes the universal features which all conventional superconductors have in common, but it is not able to make predictions of acceptable accuracy for material-specific properties. To tackle this problem, a density-functional-type theory will be presented. In this approach, the electron-phonon interaction and the electron-electron repulsion are treated on the same footing. There are no adjustable parameters suchas the ¦Ì^*of Eliashberg theory. Approximations of the universal exchange-correlation functional are derived on the basis of many-body perturbation theory [1]. The predictive power of the method is demonstrated for a variety of phonon-mediated superconductors, including elemental hydrogen and hydrides under extreme pressure, as well as multigap superconductors like MgB₂and Pb. Materials such as NbSe₂, featuring a complicated competition between superconductivity and a charge density wave at low temperature,can be fully understood [2]. The superconducting order parameter in real space is an output of our ab-initio theory. It turns out that the order parameter essentially ¡°lives¡± in the chemical bonds, i.e., is largest within the bonds [3]. For the class of MgB₂¨Ctype superconductors, we demonstrate that the degree of localization of the sigma bonds correlates with the critical temperature of the material.Routes to locally tailoring [4] the order parameter will be discussed.

[1] A Sanna, C Pellegrini, EKU Gross, PRL125, 057001 (2020).

[2] A Sanna, C Pellegrini, E Liebhaber, K Rossnagel, KJ Franke, EKU Gross, npj Quant Materials7:6(2022)

[3] A Linscheid, A Sanna, A Floris, EKU Gross, PRL115, 097002 (2015).

[4] M Schackert, T M?rkl, J Jandke, M H?lzer, S Ostanin, EKU Gross, A Ernst, W Wulfhekel, PRL114, 047002 (2015).

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