Unconventional superconductivity in weakly correlated, non-centrosymmetric $\mathrm{M}{\mathrm{o}}_3\mathrm{A}{\mathrm{l}}_2\mathrm{C}$

Abstract

Electrical resistivity, specific heat and NMR measurements classify non-centrosymmetric $\mathrm{M}{\mathrm{o}}_3\mathrm{A}{\mathrm{l}}_2\mathrm{C}$ ($\beta$-Mn type, space group $P{4}_{1}32$) as a strong-coupled superconductor with $T_c=9$~K deviating notably from BCS-like behaviour. The absence of a Hebbel-Slichter peak, a power law behaviour of the spin-lattice relaxation rate (from ${}^{27}$Al NMR), a $T^3$ temperature dependence of the specific heat and a pressure enhanced $T_c$ suggest unconventional superconductivity with a nodal structure of the superconducting gap. Relativistic DFT calculations reveal a splitting of degenerate electronic bands due to the asymmetric spin-orbit coupling, favouring a mix of spin-singlet and spin triplet components in the superconducting condensate, in absence of strong correlations among electrons.

4 pages, 5 figures