Strong surface scattering in ultrahigh mobility Bi2Se3 topological insulator crystals

TL;DR

This study investigates ultrahigh mobility Bi2Se3 crystals and finds that surface states do not significantly contribute to electrical transport, as bulk states dominate even at very low temperatures and high magnetic fields.

Contribution

It provides comprehensive experimental evidence that surface states in ultrahigh mobility Bi2Se3 are overshadowed by bulk conduction, challenging assumptions about topological surface protection.

Findings

Bulk states dominate electrical transport even at 50 mK.

Surface mobility is lower than bulk mobility despite topological protection.

No significant surface contribution observed in transport measurements.

Abstract

While evidence of a topologically nontrivial surface state has been identified in surface-sensitive measurements of Bi2Se3, a significant experimental concern is that no signatures have been observed in bulk transport. In a search for such states, nominally undoped single crystals of Bi2Se3 with carrier densities approaching 10^16 cm^-3 and very high mobilities exceeding 2 m^2 V^-1 s^-1 have been studied. A comprehensive analysis of Shubnikov de Haas oscillations, Hall effect, and optical reflectivity indicates that the measured electrical transport can be attributed solely to bulk states, even at 50 mK at low Landau level filling factor, and in the quantum limit. The absence of a significant surface contribution to bulk conduction demonstrates that even in very clean samples, the surface mobility is lower than that of the bulk, despite its topological protection.