Quantum electronics with beams of light
Researchers from the Institute of Molecular Engineering (IME) led by David Awschalom, have accidentally discovered a new way of using light to draw and erase quantum-mechanical circuits in a unique class of materials called topological insulators.
David Awschalom is a University of Chicago Professor, Deputy Director for Space, Infrastructure, and Facilities at the IME and is an Argonne Joint Appointment.
This observation came as a complete surprise.
It’s one of those rare moments in experimental science where a seemingly random event—turning on the room lights—generated unexpected effects with potentially important impacts in science and technology.
David D. Awschalom, Deputy Director, IME
In contrast to using advanced nanofabrication facilities based on chemical processing of materials, this flexible technique allows for rewritable “optical fabrication” of devices. This finding is likely to spawn new developments in emerging technologies such as low-power electronics based on the spin of electrons or ultrafast quantum computers.
The spin-polarized surface states of topological insulators (TIs) are attractive for applications in spintronics and quantum computing. 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. We demonstrate persistent, bidirectional optical control of the chemical potential of (Bi,Sb)2Te3 thin films grown on SrTiO3. By optically modulating a space-charge layer in the SrTiO3 substrates, we induce a persistent field effect in the TI films comparable to electrostatic gating techniques but without additional materials or processing.
This enables us to optically pattern arbitrarily shaped p– and n-type regions in a TI, which we subsequently image with scanning photocurrent microscopy. 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, suggesting that these phenomena could provide optical control of chemical potential in a wide range of ultrathin electronic systems.
David D. Awschalom, Andrew L. Yeats, Yu Pan, Anthony Richardella, Peter J. Mintun and Nitin Samarth, “Persistent Optical Gating of a Topological Insulator,” Science Advances, Vol. 1, no. 9, e1500640, DOI: 10.1126/sciadv.1500640, Published Online October 9, 2015.