Observation of vortex structure in MgB${}_2$ single crystals by Bitter decoration technique

Abstract

We report the observation of superconducting vortices in pure and lightly Al doped MgB${}_2$ single crystals. Low field experiments allow for the estimation of the London penetration depth, lambda ~ 1900 $\tilde{A}$ for T$\sim$6 K. Experiments in higher fields (e.g. 200 Oe) clearly show a triangular vortex lattice in both real space (13 $\hat{I}¼$m by 13 $\hat{I}¼$m Bitter decoration image of over 1000 vortices) and reciprocal space.