We report a detailed scanning tunneling microscopy study of a superconductor in a strong vortex confinement regime. This is achieved in a thin nano-island of Pb having a size d about 2-3 times the effective coherence length, and a thickness h such that h << d << λ , where λ is the effective London penetration depth. In this geometry the magnetic field evolution of local tunneling spectra reveals only two superconducting configurations to exist: zero and single vorticity. The normal state is reached at HC ≈ 0.46 T, about 6 times the critical field of bulk Pb, with no higher order vorticity observed [1]. The comparison of the acquired Scanning Tunneling Spectroscopy data with the numerically resolved Usadel equations allowed us to reveal the fundamental role played in both configurations by the circulating supercurrents.
[1] T. Cren et al., Phys. Rev. Lett. 102, 127005 (2009).
Institut des Nanosciences de Paris