Superconductivity in Chevrel phases.

Profeta G.

II - Fisica della materia
GSSI Ex ISEF - Aula C - Mercoledì 25 h 16:30 - 19:00
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Chevrel phases constitute a class of interesting materials discovered more than 40 years ago including more than 100 examples. They are ternary compounds of general stoichiometry $M_{x}Mo_{6}X_{8}$ (X = chalcogen and M = metal) and many of them show interesting superconducting properties with critical temperatures as high as 15 K and high critical magnetic fields (arount 50 Tesla). We present the results of the prediction of the superconducting phase in a Chevrel compound, $PbMo_{6}S_{8}$, within the SuperConducting Density Functional Theory (SCDFT), a first-principles theory of the superconducting phase which does not rely on any semi-empirical parameter. We succesfully predict the critical temperature of $PbMo_{6}S_{8}$ at ambient conditions highlighting the role of phase instability, electron-phonon coupling with different intra-molecular and inter-molecular phonon modes and the fundamental role of repulsive electron-electron interaction, treated from first-principles. The evolution of the superconducting critical temperature as a function of the external pressure results in excellent agreement with available experiments. Despite the interesting physical and chemical properties of Chevrel phases their fundamental explanation was still lacking: SCDFT opens the way to the systematic investigation of this large class of compounds.

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