Quantum Fractal 'Hofstadter's Butterfly' Observed in Real Material

Princeton University scientists have directly observed the quantum fractal pattern known as "Hofstadter's butterfly" in a real material for the first time. This discovery, made possible by stacking and twisting carbon atom sheets to create a moiré pattern, confirms a 1976 prediction about electron energy levels in two-dimensional crystals under a magnetic field. The "butterfly" moniker arises from the pattern's resemblance to butterfly wings when plotted against energy and magnetic field. The team, led by Ali Yazdani, used a scanning tunneling microscope (STM) to image the moiré crystals and examine electron energy levels. While initially an accidental finding during superconductivity research, the observation offers new insights into electron interactions within quantum fractals. Kevin Nuckolls, co-lead author, noted the STM's crucial role as a direct energy probe. Although immediate practical applications are not apparent, the research enhances understanding of fundamental physics and could influence future quantum material studies.