TUD

The dynamics of electrons in materials plays a fundamental role for electrical conductance, electronic excitations as well as for adsorbate interactions which are mediated by the electronic states of the substrate. Here, we investigate for the first time the quantum coherence of bulk state electrons with scanning tunneling microscopy. As a model system we use Ag(100) as no surface state is reported at the -point providing direct access to the bulk states. By measuring conductance maps above a threshold voltage, we observe standing wave patterns. These originate from electrons in a bulk band edge at the -point, which are scattered at step edges and defects. From the spatially decaying waves, the wave vector and the quantum coherence parameters - coherence length, lifetime, and line width - are determined as a function of energy. The energy of the band edge is extracted from the dispersion relation and agrees with the peak measured in scanning tunneling spectra at 1.9 eV above the Fermi energy. Theoretical calculations confirm the nature of the state elucidating the experimental findings.