  We use Angle Resolved Photoemission Spectroscopy (ARPES), Raman spectroscopy,
Low Energy Electron Diffraction (LEED) and x-ray scattering to reveal an
unusual electronically mediated charge density wave (CDW) in K0.9Mo6O17. Not
only does K0.9Mo6O17 lack signatures of electron-phonon coupling, but it also
hosts an extraordinary surface CDW, with TS CDW =220 K nearly twice that of the
bulk CDW, TB CDW =115 K. While the bulk CDW has a BCS-like gap of 12 meV, the
surface gap is ten times larger and well in the strong coupling regime. Strong
coupling behavior combined with the absence of signatures of strong
electron-phonon coupling indicates that the CDW is likely mediated by
electronic interactions enhanced by low dimensionality.
