New research reveals graphene's unusual phonon spectrum with remarkable completeness.
During crystallization, atoms are separated into broad energy bands. The electrical properties of the crystal are determined by this level spread, but it is not the only one. How atoms are arranged in space is also important, and in some rare cases a crystal may have certain symmetries that give the bands “topological” properties.
phonons Its movement within a crystal is controlled by its band structure, which can also have topological properties like those of electrons. To detect that graphene, which has already been shown to have topological electrons, also has topological phonons, Jiade Li of the China Institute of Physics and colleagues used a special type of electron spectroscopy.
Topological materials have a number of remarkable properties, including the ability to accommodate Majorana quasiparticles and nondispersive surface currents without being affected by defects or other local perturbations. This is because they arise from the global topology of the band structure rather than its local topography. To map graphene's full phonon band structure, Li and colleagues used a method that analyzes the energy electrons lose as an indicator of momentum when they bounce off a surface. A resonant phonon causes electrons to lose more energy.
Dirac points and node rings, two types of topological features that emerge when phonon bands intersect, can be found in the team's detailed map. The existence of topological phonons is not always implied by the coincidence of intersections and topological properties. But Li and his colleagues are confident that they have seen them because their map is very similar to the one obtained from theory. To create phonon diodes and other “phononic” devices, researchers' next goal is to find topological phononic edge states.
Source: physics.aps.org/articles/v16/s126
📩 15/09/2023 09:19