Unconventional superconductivity in quasi-one-dimensionalRb2Cr3As3

Abstract

Following the discovery of superconductivity in quasi-one-dimensional ${\mathrm{K}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ containing ${\left[{\left({\text{Cr}}_3{\mathrm{As}}_3\right)}^{2-}\right]}_{\infty }$ chains (J. K. Bao et al., arXiv:1412.0067), we succeeded in synthesizing an analogous compound, ${\mathrm{Rb}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$, which also crystallizes in a hexagonal lattice. The replacement of K by Rb results in an expansion of the $a$ axis by 3%, indicating a weaker interchain coupling in ${\mathrm{Rb}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$. Bulk superconductivity emerges at 4.8 K, above which the normal-state resistivity shows a linear temperature dependence up to 35 K. The estimated upper critical field at zero temperature exceeds the Pauli paramagnetic limit by a factor of 2. Furthermore, the electronic specific-heat coefficient extrapolated to zero temperature in the mixed state increases with $\sqrt{H}$, suggesting the existence of nodes in the superconducting energy gap. Hence ${\mathrm{Rb}}_2{\mathrm{Cr}}_3{\mathrm{As}}_3$ manifests itself as another example of an unconventional superconductor in the ${\mathrm{Cr}}_3{\mathrm{As}}_3$-chain based system.