APS -APS March Meeting 2017 - Event - Enhancing superconductivity of A$_{mathrm{3}}$C$_{mathrm{60}}$ fullerides : mechanism and its relation to optically stimulated superconductivity

摘要

Recently, there was a remarkable observation of the nonequilibrium superconductivity (SC) up to extasciitilde 100 K in K$_{mathrm{3}}$C$_{mathrm{60}}$ fullerides by terahertz (THz) optical pump prove experiment.[Ref.[1]] This temperature (T) of nonequilibrium SC is much higher than T$_{mathrm{c}}$ of equilibrium (20K). Motivated by the experiment, we investigate how perturbation effects on SC of A$_{mathrm{3}}$C$_{mathrm{60}}$ by using the strong-coupling model. We have shown that the perturbation such that smaller Coulomb interaction in two of three LUMO of C$_{mathrm{60}}$ enhances T$_{mathrm{c}}$ of fullerides, potentially up to factor of 1.8. We have shown that this type of perturbation could be realized in the pump prove experiment by T$_{mathrm{1u}}$(4) phonon excitation which is suggested to be pumped from the THz light. Other types of perturbations are detrimental to the SC of fullerides. The mecha perturbation could be realized in the pump prove experiment by T$_{mathrm{1u}}$(4) phonon excitation which is suggested to be pumped from the THz light. Other types of perturbations are detrimental to the SC of fullerides. The mechanism of T$_{mathrm{c}}$ of fullerides is that (i) stabilization of spin-singlet states, and (ii) preservation orbital fluctuation. This finding provides guideline for experiment to observe an enhancement of T$_{mathrm{c}}$ and basis for theoretical investigation of nonequilibrium phenomena of fullerides. [1] M. Mitrano et al., Nature 530, 461 (2016).