  We investigate periodical oscillations in the conductance of suspended Au and
Pt atomic chains during elongation under mechanical stress. Analysis of
conductance and shot noise measurements reveals that the oscillations are
mainly related to variations in a specific conduction channel as the chain
undergoes transitions between zigzag and linear atomic configurations. The
calculated local electronic structure shows that the oscillations originate
from varying degrees of hybridization between the atomic orbitals along the
chain as a function of the zigzag angle. These variations are highly dependent
on the directionality and symmetry of the relevant orbitals, in agreement with
the order-of-magnitude difference between the Pt and Au oscillation amplitudes
observed in experiment. Our results demonstrate that the sensitivity of
conductance to structural variations can be controlled by designing
atomic-scale conductors in view of the directional interactions between atomic
orbitals.
