Bi Nanowires as Topological Insulators

1. Bi Nanowires as Topological Insulators Joshua B. Halpern, Howard University, DMR 0611595 For topological insulators (TI) conduction only occurs on the surface, but not inside of the material. A group lead by Tito Huber of Howard University and the PREM, has demonstrated that Bi nanowires become topological insulators after undergoing a semimetal-semiconductor transition driven by quantum confinement for diameters close to 50 nm. Topological insulator behavior consisting of ultrahigh mobilities and enhanced thermopower has been predicted. For Bi nanowires, the surface electrons have high mobilities, exceeding 2(m2)/(V sec), two thirds of that for graphene, and contribute strongly to the thermopower, dominating for temperatures T< 100 K. The surface thermopower is - 1.2 T microvolt/(K2), a value consistent with theory, raising the prospect of developing nanoscalethermoelectrics based on surface bands. Surface state band mobility and thermopower in semiconducting bismuth nanowires”, T. E. Huber, A. Adeyeye, A. Nikolaeva, L. Konopko, R. C. Johnson, and M. Graf. Physical Review B83, 235414 (2011). “Thermoelectric prospects of nanomaterials with spin-orbit surface bands”, T. E. Huber, K. Owusu, S. Johnson, A. Nikolaeva, L. Konopko, R. C. Johnson, and M. J. Graf. Journal of Applied Physics111, 043709 (2012). Charge density as a function of the nanowireinverse diameter, showing how quantum confinement turns Bi wires into a bulk insulator Bi nanowire thermopowera as a function of temperature T.

2. Joshua B. Halpern, Howard University, DMR 0611595 Bi Nanowires as Topological Insulators A group lead by Tito Huber of Howard University and the Howard/Hopkins/PGCC PREM, has demonstrated that Bi nanowires become topological insulators after undergoing a semimetal-semiconductor transition driven by quantum confinement for diameters close to 50 nm. In the Bi nanowires, the researchers have measured high mobilities, exceeding 2(m2)/(V sec), two thirds of that for graphene, and very high surface thermopowers of the order of - 1.2 T microvolt/(K2), a value consistent with theory, raising the prospect of developing nanoscalethermoelectrics based on surface bands See “Surface state band mobility and thermopower in semiconducting bismuth nanowires”, T. E. Huber, A. Adeyeye, A. Nikolaeva, L. Konopko, R. C. Johnson, and M. Graf. Physical Review B83, 235414 (2011). “Thermoelectric prospects of nanomaterials with spin-orbit surface bands”, T. E. Huber, K. Owusu, S. Johnson, A. Nikolaeva, L. Konopko, R. C. Johnson, and M. J. Graf. Journal of Applied Physics111, 043709 (2012). For more information contact: Prof. Tito Huber thuber@howard.eduDepartment of Chemistry Howard UniversityWashington, DC 20050