Observation of the Wannier-Stark ladder in plasmonic waveguide arrays

TL;DR

This paper demonstrates the experimental observation of Wannier-Stark ladders and Bloch oscillations in plasmonic waveguide arrays, revealing wave dynamics analogous to electronic systems under external fields.

Contribution

It provides the first direct visualization of Wannier-Stark ladders and Bloch oscillations in plasmonic waveguides using leakage radiation microscopy.

Findings

Observation of periodic breathing of wavepackets.

Detection of oscillatory motion in waveguide arrays.

Identification of equally spaced modes in spectra.

Abstract

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.