NMR study of the Mott transitions to superconductivity in the two Cs_3C_60 phases

TL;DR

This study uses NMR and magnetometry to investigate the Mott transition to superconductivity in Cs_3C_60, revealing that inter-ball distance governs electronic phases despite different magnetic ground states.

Contribution

It provides the first comparative NMR analysis of A15 and FCC Cs_3C_60, showing similar phase diagrams driven by inter-ball distance despite different magnetic ground states.

Findings

Both phases exhibit a first-order Mott transition to superconductivity.

The phase diagrams are superimposed when plotted against unit volume per C_60.

Inter-ball distance is the key parameter controlling electronic behavior.

Abstract

We report an NMR and magnetometry study on the expanded intercalated fulleride Cs_3C_60 in both its A15 and face centered cubic structures. NMR allowed us to evidence that both exhibit a first-order Mott transition to a superconducting (SC) state, occuring at distinct critical pressures p_c and temperatures T_c. Though the ground state magnetism of the Mott phases differs, their high $T$ paramagnetic and SC properties are found similar, and the phase diagrams versus unit volume per C_60 are superimposed. Thus, as expected for a strongly correlated system, the inter-ball distance is the relvevant parameter driving the electronic behavior and quantum transitions of these systems.