Superconducting intermediate state of white tin studied by muon-spin-rotation spectroscopy

The local magnetic field in the bulk of superconducting single crystal β tin was measured near and across the transition between the normal (N) and intermediate (I) state at T=0.08 K. With varying applied field Hₐ, the data indicate a reversible phase transition within the I state at Hₜ≈295 Oe, interpreted as a transition from the laminar to a tubular structure. Near the →IN transition, occurring at HcI=0.98Hc0=300 Oe, the field B in the N domains is strongly inhomogeneous with B̄<Hc0, it grows with the decrease of Hₐ towards the value Hc0=305.5±0.5 Oe. On lowering Hₐ in the N state, a large ``field supercooling'' (δH/Hc≈6%) of this state was observed.