The photoconductive control of excited electrons in topologically protected states open new perspectives for the transmission of of spin polarized currents. Our data show that the interplay of surface and bulk carrier dynamics in photoexcited Bi2.2Te3 determines an essential parameter for photoconductivity - the balance between excess electrons and holes in the Dirac cone. If correctly mastered, the band lineup can be advantageously used to confine photoexicted electrons in the Dirac cones while the photoexcited holes diffuse in bulk-like states. As shown in the picture, this charge separation at the interface results in a transient shift of the chemical potential by as much as 100 meV. The surprisingly long lifetime of the Dirac cone filling can be viewed as the metastable tuning of a Schottky barrier and suggests interesting optoelectronic applications.
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 Unraveling the Dirac fermion dynamics of the bulk-insulating topological system Bi2Te2Se, E. Papalazarou, L. Khalil, M. Caputo, L. Perfetti, N. Nilforoushan, H. Deng, Z. Chen, S. Zhao, A. Taleb-Ibrahimi, M. Konczykowski, A. Hruban, A. Wolos, A. Materna, L. Krusin-Elbaum, and M. Marsi, Physical Review Materials 2, 104202 (2018).