Penetration depth study of the type-I superconductor PdTe2.

Superconductivity in the topological non-trivial Dirac semimetal PdTe2 was recently shown to be type-I. We hereby report measurements of the relative magnetic penetration depth, [Formula: see text], on several single crystals using a high precision tunnel diode oscillator technique. The temperature variation [Formula: see text] follows an exponential function for [Formula: see text], consistent with a fully-gapped superconducting state and weak or moderately coupling superconductivity. By fitting the data we extract a [Formula: see text]-value of ∼500 nm. The normalized superfluid density is in good agreement with the computed curve for a type-I superconductor with nonlocal electrodynamics. Small steps are observed in [Formula: see text], which possibly relates to a locally lower [Formula: see text] due to defects in the single crystalline sample.

Macroscopic phase separation of superconductivity and ferromagnetism in Sr0.5Ce0.5FBiS2-x Se x revealed by µSR.

The compound Sr0.5Ce0.5FBiS2 belongs to the intensively studied family of layered BiS2 superconductors. It attracts special attention because superconductivity at T sc = 2.8 K was found to coexist with local-moment ferromagnetic order with a Curie temperature T C = 7.5 K. Recently it was reported that upon replacing S by Se T C drops and ferromagnetism becomes of an itinerant nature. At the same time T sc increases and it was argued superconductivity coexists with itinerant ferromagnetism. Here we report a muon spin rotation and relaxation study (µSR) conducted to investigate the coexistence of superconductivity and ferromagnetic order in Sr0.5Ce0.5FBiS2-x Se x with x = 0.5 and 1.0. By inspecting the muon asymmetry function we find that both phases do not coexist on the microscopic scale, but occupy different sample volumes. For x = 0.5 and x = 1.0 we find a ferromagnetic volume fraction of ~8 % and ~30 % at T = 0.25 K, well below T C = 3.4 K and T C = 3.3 K, respectively. For x = 1.0 (T sc = 2.9 K) the superconducting phase occupies most (~64 %) of the remaining sample volume, as shown by transverse field experiments that probe the Gaussian damping due to the vortex lattice. We conclude ferromagnetism and superconductivity are macroscopically phase separated.