Strong pressure dependence of the magnetic penetration depth in single crystals of the heavy-fermion superconductor CeCoIn5 studied by muon spin rotation.

In the tetragonal heavy fermion system CeCoIn(5) the unconventional superconducting state is probed by means of muon spin rotation. The pressure dependence (0-1 GPa) of the basal-plane magnetic penetration depth (λ(a)), the penetration depth anisotropy (γ = λ(c)/λ(a)) and the temperature dependence of 1/λ(i)(2) (i = a, c) were studied in single crystals. A strong decrease of λ(a) with pressure was observed, while γ and λ(i)(2)(0)/λ(i)(2)(T) are pressure independent. A linear relationship between 1/λ(a)(2)(270 mK) and T(c) was also found. The large decrease of λ(a) with pressure is the signature of an increase of the number of superconducting quasiparticles by a factor of about 2.