Spin Dynamics at the Mott Transition and in the Metallic State of the Cs_{3}C_{60} Superconducting Phases

TL;DR

This study investigates spin dynamics in Cs3C60 across the Mott transition using NMR relaxation data, revealing enhanced electronic correlations near the transition and temperature-dependent variations linked to a critical point.

Contribution

It provides new insights into the spin relaxation behavior and electronic correlations in Cs3C60 near the Mott transition, highlighting the role of a liquid-gas like critical point.

Findings

(T_{1}T)^{-1} matches metallic Korringa values above p_c

Enhanced (T_{1}T)^{-1} below the maximum T_c indicates strong correlations

Large temperature variation of p_c suggests a critical point in the Mott transition

Abstract

We present here ^{13}C and ^{133}Cs NMR spin lattice relaxation T_{1} data in the A15 and fcc-Cs_{3}C_{60} phases for increasing hydrostatic pressure through the transition at p_{c} from a Mott insulator to a superconductor. We evidence that for p>> p_{c} the (T_{1}T)^{-1} data above T_{c} display metallic like Korringa constant values which match quantitatively previous data taken on other A_{3}C_{60} compounds. However below the pressure for which T_{c} goes through a maximum, (T_{1}T)^{-1} is markedly increased with respect to the Korringa values expected in a simple BCS scenario. This points out the importance of electronic correlations near the Mott transition. For p > p_{c} singular T dependences of (T_{1}T)^{-1} are detected for T >> T_{c}. It will be shown that they can be ascribed to a large variation with temperature of the Mott transition pressure p_{c} towards a liquid-gas like critical point, as found at high T for usual Mott transitions.