Unconventional superconducting phase in the weakly correlated noncentrosymmetric Mo₃Al₂C compound

Abstract

Electrical resistivity, specific-heat, and NMR measurements classify noncentrosymmetric Mo3Al2C (β-Mn type, space group P4132) as a strong-coupled superconductor with Tc=9 K deviating notably from BCS-type behavior. The absence of a Hebbel-Slichter peak, a power-law behavior of the spin-lattice relaxation rate (from 27Al NMR), an electronic specific heat strongly deviating from BCS model and a pressure enhanced Tc suggest unconventional superconductivity with possibly a nodal structure of the superconducting gap. Relativistic density-functional theory calculations reveal a splitting of degenerate electronic bands due to the asymmetric spin-orbit coupling, favoring a mix of spin-singlet and spin-triplet components in the superconducting condensate, in absence of strong correlations among electrons.