Fractal defect states in the Hofstadter butterfly

We investigate the electronic properties in the Bloch electron on a two-dimensional lattice with vacancies in the uniform magnetic field. We show that a single vacancy site introduced to the system creates a defect energy level in every single innumerable fractal energy gap in the Hofstadter butterfly. The wave functions of different defect levels have all different localization lengths depending on their fractal generations, and they can be described by a single universal function after an appropriate fractal scaling. We also show that each defect state has its own characteristic orbital magnetic moment, which is exactly correlated to the gradient of the energy level in the Hofstadter diagram. Probing the spatial nature of the defect-localized states provides a powerful way to elucidate the fractal nature of the Hofstadter butterfly.

Automated summary

The study found that introducing a single defect site in a two-dimensional lattice of Bloch electrons in a uniform magnetic field creates a defect energy level in each energy gap of the Hofstadter butterfly. The wave functions of different defect levels have different localization lengths, but can be described by a single universal function after fractal scaling. Each defect state has its own characteristic orbital magnetic moment correlated to the energy level gradient in the Hofstadter diagram, providing insight into the fractal nature of the Hofstadter butterfly.