Observation of the sliding phason mode of the incommensurate magnetic texture in Fe/Ir(111)

The nanoscopic magnetic texture forming in a monolayer of iron on the (111) surface of iridium, Fe/Ir(111),
is spatially modulated and uniaxially incommensurate with respect to the crystallographic periodicities.
As a consequence, a low-energy magnetic excitation is expected that corresponds to the sliding of the
texture along the incommensurate direction, i.e., a phason mode, which we explicitly confirm with
atomistic spin simulations. Using scanning tunneling microscopy (STM), we succeed to observe this
phason mode experimentally. It can be excited by the STM tip, which leads to a random telegraph noise in
the tunneling current that we attribute to the presence of two minima in the phason potential due to the
presence of disorder in our sample. This provides the prospect of a floating phase in cleaner samples and,
potentially, a commensurate-incommensurate transition as a function of external control parameters.