Geometric frustration of particle motion in a kagome lattice causes the single-particle band structure to exhibit a dispersion-less, flat band. Generally, frustration can cause a vast degeneracy of low-energy states, and instabilities in the presence of atomic interactions may lead to the manifestation of exotic states of matter. The kagome lattice, a pattern of vertex-sharing triangular plaquettes, offers the highest degree of frustration among two-dimensional lattice geometries. We create an optical kagome lattice by superimposing two optical triangular lattices made from laser light with commensurate wavelengths. We probe the band structure of the kagome lattice by preparing a Bose-Einstein condensate in excited Bloch states of the lattice, and then measuring the atoms’ group velocity via the atomic momentum distribution. We find that atomic interactions renormalize the kagome lattice band structure, significantly increasing the dispersion of the third band, which, according to non-interacting band theory, should be nearly flat (dispersion-less). Measurements at various lattice depths and gas densities agree quantitatively with predictions from the lattice Gross-Pitaevskii equation, which indicates that the observed band structure distortion, onset by atomic interactions, is caused by the distortion of the overall lattice potential away from the kagome geometry.
Join Dr. Charles Brown, postdoctoral scholar and Ford Foundation fellow at the University of California - Berkeley, as our speaker at 5:30 PM EST on September 29th for NSBP Innovate Seminar Series: "Interacting Bosons in the Flat Band of an Optical Kagome Lattice".
The series is a forum for NSBP members to share their research ideas & projects in a non-specialist way with a wide audience. The 30-minute talk (followed by 15 minutes of Q&A) will be a Zoom Webinar, and recorded. It will be available to the whole world soon after the event at KITP Online.