Spin dynamics at the Mott transition and in the metallic state of the Cs3C60 superconducting phases
Laboratoire de Physique des Solides, Université Paris-Sud 11, CNRS UMR 8502 - 91405 Orsay, France, EU
2 Dipartimento di Fisica, Università di Parma - Via G. P. Usberti 7/a, 43100 Parma, Italy, EU
Accepted: 22 March 2011
We present here 13C and 133Cs NMR spin lattice relaxation T1 data in the A15 and fcc-Cs3C60 phases for increasing hydrostatic pressure through the transition at pc from a Mott insulator to a superconductor. We evidence that for p ≫ pc the (T1T)− 1 data above Tc display metallic-like Korringa constant values which match quantitatively previous data taken on other A3C60 compounds. However below the pressure for which Tc goes through a maximum, (T1T)− 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 ≳ pc singular T-dependences of (T1T)− 1 are detected for T ≫ Tc. It will be shown that they can be ascribed to a large variation with temperature of the Mott transition pressure pc towards a liquid-gas-like critical point, as found at high T for usual Mott transitions.
PACS: 71.30.+h – Metal-insulator transitions and other electronic transitions / 74.70.Wz – Carbon-based superconductors / 74.25.nj – Nuclear magnetic resonance
© EPLA, 2011