Electronic states in disordered conductors on the verge of localization are predicted to exhibit critical spatial characteristics indicative of the proximity to a metal‑insulator phase transition. We have used scanning tunneling microscopy to visualize electronic states in Ga1‑xMnxAs samples close to this transition. Our measurements show that doping-induced disorder produces strong spatial variations in the local tunneling conductance across a wide range of energies. Near the Fermi energy, where spectroscopic signatures of electron-electron interaction are the most prominent, the electronic states exhibit a diverging spatial correlation length. Power-law decay of the spatial correlations is accompanied by log-normal distributions of the local density of states and multifractal spatial characteristics. Our method can be used to explore critical correlations in other materials close to a quantum critical point.
Published in Science:
Visualizing Critical Correlations near the Metal-Insulator Transition in Ga1‑xMnxAs, Anthony Richardella, Pedram Roushan, Shawn Mack, Brian Zhou, David A. Huse, David D. Awschalom, Ali Yazdani, Science 327, 665 (2010). (Article)