Real-Space Vortex Glass Imaging and the Vortex Phase Diagram of SnMo6S8

Using scanning tunneling microscopy at 400 mK, we have obtained maps of around 100 vortices in SnMo6S8 from 2-9 T. The orientational and positional disorder at 5 and 9 T show that these are the first large-scale images of a vortex glass. At higher temperature a magnetization peak effect is observed, whose upper boundary coincides with a lambda anomaly in the specific heat. Our data favor a kinetic glass description of the vortex melting transition, indicating that vortex topological disorder persists at fields and temperatures far below the peak effect in low-T-c superconductors.