Measurement of two-state energy landscapes on amorphous hafnium diboride surface by direct observation of dynamics

Direct visualization of free energy landscape for individual Cooperatively Rearranging Regions (CRRs) is important in glassy dynamics, both for the bulk and the surface. We used scanning tunneling microscopy to track individual CRRs on amorphous hafnium diboride surface, temporally from microseconds to hours with sub-nanometer spatial resolution. CRRs have a diameter of $\sim$5 atoms and mostly relax in a two-state fashion. From single cluster tunneling current traces, we can reconstruct local free energy landscapes, complete with energy difference, barrier height, a numerically defined reaction corrdinate and shape of the free energy minima.