  We studied the noise spectra of molecule-free and molecule-containing
mechanically controllable break junctions. Both types of junctions revealed
typical 1/ f noise characteristics at different distances between the contacts
with square dependence of current noise power spectral density on current.
Additional Lorentzian-shape (1/ f 2) noise components were recorded only when
nanoelectrodes were bridged by individual 1,4 benzenediamine molecule. The
characteristic frequency of the revealed 1/ f 2 noise related to a single
bridging molecule correlates with the lock-in current amplitudes. The recorded
behavior of Lorentzian-shape noise component as a function of current is
interpreted as the manifestation of a dynamic reconfiguration of molecular
coupling to the metal electrodes. We propose a phenomenological model that
correlates the charge transport via a single molecule with the reconfiguration
of its coupling to the metal electrodes. Experimentally obtained results are in
good agreement with theoretical ones and indicate that coupling between the
molecule metal electrodes is important aspect that should be taken into
account.
