Spin dynamics at the Mott transition and in the metallic state of the Cs₃C₆₀ superconducting phases

Author： Ihara Y. Alloul H. Wzietek P. Pontiroli D. Mazzani M. Riccò M.

E-ISSN： 1286-4854|94|3|37007-37007

ISSN： 0295-5075

Source： EPL (EUROPHYSICS LETTERS), Vol.94, Iss.3, 2011-04, pp. : 37007-37007

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Abstract

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 p_c from a Mott insulator to a superconductor. We evidence that for p ≫ p_c the (T₁T)^{− 1} data above T_c display metallic-like Korringa constant values which match quantitatively previous data taken on other A₃C₆₀ compounds. However below the pressure for which T_c 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 ≳ p_c singular T-dependences of (T₁T)^{− 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.