Nodal superconducting gap structure in the quasi-one-dimensional Cs₂Cr₃As₃ investigated using μsR measurements

The superconducting ground state of the newly discovered superconductor Cs₂Cr₃As₃ [Tc ∼ 2.1(1) K] with a quasione-dimensional crystal structure has been investigated using magnetization and muon-spin relaxation and rotation (μSR), both zero-field (ZF) and transverse-field (TF), measurements. Our ZF μSR measurements reveal the presence of spin fluctuations below 4K and the ZF relaxation rate (λ) shows an enhancement below Tc ∼2.1 K, which might indicate that the superconducting state is unconventional. This observation suggests that the electrons are paired via unconventional channels such as spin fluctuations, as proposed on the basis of theoretical models. Our analysis of the TF μSR results shows that the temperature dependence of the superfluid density is fitted better with a nodal gap structure than an isotropic s-wave model for the superconducting gap. The observation of a nodal gap in Cs₂Cr₃As₃ is consistent with that observed in the isostructural K2Cr3As3 compound through TF μSR measurements. Furthermore, from our TF μSR study we have estimated the magnetic penetration depth of the polycrystalline sample λL(0) = 954 nm, superconducting carrier density ns = 4.98 × 1026m-3, and carriers' effective-mass enhancement m∗ = 1.61me.