Unconventional superconductivity in weakly correlated, non-centrosymmetric $\rm{Mo_3Al_2C}$

TL;DR

This study identifies unconventional superconductivity in non-centrosymmetric Mo3Al2C, characterized by nodal gaps and mixed pairing states, supported by experimental measurements and relativistic DFT calculations.

Contribution

It provides the first comprehensive experimental and theoretical analysis of superconductivity in Mo3Al2C, highlighting its unconventional nature and the role of spin-orbit coupling.

Findings

Strong-coupled superconductor with Tc = 9 K

Evidence of nodal superconducting gap structure

Band splitting due to spin-orbit coupling

Abstract

Electrical resistivity, specific heat and NMR measurements classify non-centrosymmetric $\rm Mo_3Al_2C$ ($\beta$-Mn type, space group $P4_132$) 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.