Absolute Penetration Depth in MgB$_{2}$

Absolute penetration depth measurements were carried out on single crystals of MgB$_{2}$. $\lambda $(0) was determined by sputtering an Al film onto the sample crystal and measuring the change in Meissner screening as the Al film expels flux. The change in screening was measured with a tunnel diode oscillator [1]. Several samples were sputtered with films of different thicknesses and measured. Thickness dependent changes in Hc and Tc of the thin Al films provided a self-consistency check on properties of the films. Subsequent analysis using FIB/SEM and AFM independently measured the film thickness and roughness. Work at UIUC supported by NSF DMR-05-03882. Work at the Ames Laboratory was supported by the Department of Energy, Basic Energy Sciences under Contract No. DE-AC02-07CH11358. [1] R. Prozorov, et al, Appl. Phys. Lett. 77, 4202 (2000)