An inter-MRSEC collaboration between the University of Chicago and the Pennsylvania State University led to the discovery of a new technique that enables bidirectional control of the chemical potential in a topological insulator (TI). A central challenge with these materials is to reliably tune the chemical potential of their electrons with respect to the Dirac point and the bulk bands, thereby hindering research and potential applications. This all-optical effect is persistent and allows for direct patterning and imaging of p-n junctions . The ability to optically write and erase mesoscopic electronic structures in a TI may aid in the investigation of the unique properties of the topological insulating phase. The gating effect also generalizes to other thin-film materials, implying that these phenomena could provide optical control of chemical potential in a wide range of ultrathin electronic systems. The persistence and bidirectionality of the optical gating effect also suggest its potential relevance as a platform for optically defined reconfigurable electronics. The results were highlighted in the Science section of the New York Times, and discussed on National Public Radio. It recently was selected as a finalist for the NPR Golden Mole Award.
Schematic of measurement setup, showing Van der Pauw indices of the electrical contacts
Schematic of the band structure of (Bi,Sb)2Te3, showing the effect of optical illumination on the chemical potential μ of the TI layer (dotted line and arrows)
Photocurrent images showing the longitudinal component of chemical potential gradients due to p-n junctions patterned with the optical gating technique. The field of view was first initialized to p-type by exposure to red light from a HeNe laser.
 “Persistent optical gating of a topological insulator,” Andrew L. Yeats, Yu Pan, Anthony Richardella, Peter J. Mintun, Nitin Samarth, and David D. Awschalom, Science Advances 1, e1500640 (2015); "An Error Leads to a New Way to Draw, and Erase, Computing Circuits," John Markoff, New York Times, October 9 (2015); "5 Brilliant Scientific Accidents," Skunk Bear: Science from NPR, March 1 (2016).