Anisotropic magnetoconductance in quench-condensed ultrathin beryllium films

Near the superconductor-insulator (S-I) transition, quench-condensed ultrathin Be films show a large magnetoconductance which is highly anisotropic in the direction of the applied field. Film conductance can drop as much as seven orders of magnitude in a weak perpendicular field (≤1 T), but is insensitive to a parallel field in the same field range. We believe that this negative magnetoconductance is due to the field dephasing of the superconducting pair wave function. This idea enables us to extract the finite superconducting phase coherence length, Lφ, in nearly superconducting films. Our data indicates that this phase coherence persists even in highly insulating films in the vicinity of the S-I transition. In nearly insulating films, we observe that at low temperatures Lφ decreases with decreasing temperature. This is rather counterintuitive since Lφ is expected to increase with decreasing temperature as inelastic phonon scattering is suppressed.