Nodal Superconducting gap structure in the quasi-one-dimensional Cs2Cr3As3 investigated using muSR measurements

The superconducting ground state of the newly discovered superconductor Cs2Cr3As3 [Tc ~ 2.1(1)K] with a quasi one-dimensional crystal structure has been investigated using magnetization and muon-spin relaxation and rotation (muSR), both zero-field (ZF) and transverse-field (TF), measurements. Our ZF muSR measurements reveal the presence of spin fluctuations below 4 K and the ZF relaxation rate (lambda) 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 muSR 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 muSR measurements. Furthermore, from our TF muSR study we have estimated the magnetic penetration depth of the polycrystalline sample lambda_L(0) = 954 nm, superconducting carrier density n_s = 4.98 10^26 m^-3, and carriers’ effective-mass enhancement m*= 1.61me