Surface state band mobility and thermopower in semiconducting bismuth nanowires

TL;DR

This study investigates the surface state band mobility and thermopower in semiconducting bismuth nanowires, revealing high surface electron mobilities and their significant contribution to thermopower, with implications for nanoscale thermoelectric applications.

Contribution

It provides experimental evidence of high surface electron mobilities and thermopower in bismuth nanowires, highlighting the role of surface states in thermoelectric performance.

Findings

Surface electrons have mobilities exceeding 2 m^2/(V·s).

Surface thermopower is approximately -1.2 T μV/K^2.

Surface states dominate thermopower below 100 K.

Abstract

Many thermoelectrics like Bi exhibit Rashba spin-orbit surface bands for which topological insulator behavior consisting of ultrahigh mobilities and enhanced thermopower has been predicted. Bi nanowires realize surface-only electronic transport since they become bulk insulators when they undergo the bulk semimetal-semiconductor transition as a result of quantum confinement for diameters close to 50 nm. We studied 20-, 30-, 50- and 200-nm trigonal Bi wires. Shubnikov-de Haas magnetoresistance oscillations caused by surface electrons and bulklike holes enable the determination of their densities and mobilities. Surface electrons have high mobilities exceeding 2(m^2)/(Vsec) and contribute strongly to the thermopower, dominating for temperatures T< 100 K. The surface thermopower is - 1.2 T microvolt/(K^2), a value that is consistent with theory, raising the prospect of developing nanoscale thermoelectrics based on surface bands.