Unconventional superconductivity in quasi-one-dimensional Rb${}_2$Cr${}_3$As${}_3$

Abstract

Following the discovery of superconductivity in quasi-one-dimensional K${}_2$Cr${}_3$As${}_3$ containing [(Cr${}_3$As${}_3$)${}^{2-}$]${}_{\infty }$ chains [J. K. Bao et al., arXiv: 1412.0067 (2014)], we succeeded in synthesizing an analogous compound, Rb${}_2$Cr${}_3$As${}_3$, which also crystallizes in a hexagonal lattice. The replacement of K by Rb results in an expansion of $a$ axis by 3\%, indicating a weaker interchain coupling in Rb${}_2$Cr${}_3$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 two. Furthermore, the electronic specific-heat coefficient extrapolated to zero temperature in the mixed state increases with $\sqrt{H}$, suggesting existence of nodes in the superconducting energy gap. Hence Rb${}_2$Cr${}_3$As${}_3$ manifests itself as another example of unconventional superconductor in the Cr${}_3$As${}_3$-chain based system.

5 pages, 4 figures, crystal structure data updated