Structure and physical properties of the noncentrosymmetric superconductorMo3Al2C

Abstract

We have synthesized polycrystalline samples of the noncentrosymmetric superconductor ${\text{Mo}}_{3}{\text{Al}}_{2}\text{C}$ by arc and RF melting, measured its transport, magnetic and thermodynamic properties, and computed its band structure. Experimental results indicate a bulk superconducting transition at ${T}_{c}\ensuremath{\sim}9.2\text{ }\text{K}$ while the density of states at the Fermi surface is found to be dominated by $\text{Mo}\text{ }d$ orbitals. Using the measured values for the lower critical field ${H}_{c1}$, upper critical field ${H}_{c2}$, and the specific heat $C$, we estimated the thermodynamic critical field ${H}_{c}(0)$, coherence length $\ensuremath{\xi}(0)$, penetration depth $\ensuremath{\lambda}(0)$, and the Ginzburg-Landau parameter $\ensuremath{\kappa}(0)$. The specific-heat jump at ${T}_{c}$, $\ensuremath{\Delta}C/\ensuremath{\gamma}{T}_{c}=2.14$, suggests that ${\text{Mo}}_{3}{\text{Al}}_{2}\text{C}$ is moderately to strongly coupled, consistent with the fast opening of the gap, as evidenced by the rapid release of entropy below ${T}_{c}$ from our electronic specific-heat measurements. Above 2 K the electronic specific heat exhibits the power-law behavior, suggesting that synthesis of single crystals and measurements at lower temperature are needed to establish whether the gap is anisotropic. The estimated value of the upper critical field ${H}_{c2}(0)$ is close to the calculated Pauli limit, therefore further studies are needed to determine whether the absence of an inversion center results in a significant admixture of the triplet component of the order parameter.