Visualizing Critical Correlations Near the Metal-Insulator Transition in Ga₁₋xMnxAs

• Published in: Science (American Association for the Advancement of Science) Vol. 327; no. 5966; pp. 665 - 669
• Main Authors: Richardella, Anthony, Roushan, Pedram, Mack, Shawn, Zhou, Brian, Huse, David A, Awschalom, David D, Yazdani, Ali
• Format: Journal Article
• Language: English
• Published: Washington, DC American Association for the Advancement of Science 05.02.2010
• Subjects: Condensed matter: electronic structure, electrical, magnetic, and optical properties; Electron states; energy; Exact sciences and technology; lognormal distribution; Metal-insulator transitions and other electronic transitions; phase transition; Physics; scanning tunneling microscopy; spectroscopy; Gallium arsenides; Impurity density; Metal-insulator transition; Doping; Tunnel effect; Manganese additions; Multifractal system; Electronic density of states; Order disorder; Spatial variation; Electron-electron interactions; Scanning tunneling microscopy; Fermi level; III-V semiconductors
• ISSN: 0036-8075
• DOI: 10.1126/science.1183640

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 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.