  Evanescently coupled waveguides are a powerful platform to study and
visualize the wave dynamics in tight-binding systems. Here, we investigate the
propagation of surface plasmon polaritons in arrays of dielectric loaded
surface plasmon polariton waveguides with a propagation constant gradient
acting as an effective external potential. Using leakage radiation microscopy,
we observe in real-space for single site excitation a periodic breathing of the
wavepacket and an oscillatory motion in the case of Gaussian excitation of
multiple waveguides. The corresponding momentum resolved spectra are composed
of sets of equally spaced modes. We interpret these observation as the
plasmonic analogues of Bloch oscillations and the Wannier-Stark ladder,
respectively.
