Unified understanding of superconductivity and Mott transition in alkali-doped fullerides from first principles

TL;DR

This paper uses first-principles calculations to accurately model alkali-doped fullerides, successfully reproducing their complex phase diagram and high critical temperatures, revealing the interplay of electronic correlations and phonons.

Contribution

It introduces a comprehensive first-principles approach that captures both superconductivity and Mott physics in fullerides without prior assumptions.

Findings

Reproduces the experimental phase diagram including Mott insulator and superconductor phases.

Quantitatively matches the critical temperatures of superconductivity.

Identifies the competition between Hund's coupling and Jahn-Teller phonons as key to the phase behavior.

Abstract

Alkali-doped fullerides A3C60 (A=K, Rb, Cs) are surprising materials where conventional phonon-mediated superconductivity and unconventional Mott physics meet, leading to a remarkable phase diagram as a function of the volume per C60 molecule. Here we address these materials with a state-of-the-art calculation, where we construct a realistic low-energy model from first principles without using a priori information other than the crystal structure and solve it with an accurate many-body theory. Remarkably our scheme comprehensively reproduces the experimental phase diagram including the low-spin Mott-insulating phase next to the superconducting phase. Most remarkably, the critical temperature Tc's calculated from first principles quantitatively reproduce the experimental values. The driving force behind the surprising phase diagram of A3C60 is a subtle competition between Hund's coupling and Jahn-Teller phonons, which leads to an effectively inverted Hund's coupling. Our results establish that the fullerides are the first members of a novel class of molecular superconductors in which the multiorbital electronic correlations and phonons cooperate to reach high-Tc s-wave superconductivity.