Probing hot-electron dynamics at surfaces with a cold scanning tunneling microscope

We report on a novel approach to measure the phase relaxation length and fe mtosecond lifetime of hot quasiparticles on metal surfaces. A 4 K scanning tunneling microscope has been used to study the spatial decay of interferen ce patterns in the local density of states for surface state electrons on A g(111) and Cu(111). This decay is governed by inelastic; electron-electron scattering. We find a (E - E-F)(-2) energy dependence of the lifetimes for both Ag and Cu, and our values are comparable to the corresponding bulk ele ctron lifetimes. This indicates that electron-electron interaction of hot s urface state electrons with the Fermi sea is dominated by the underlying bu lk electrons. [S0031-9007(99)09260-1].