Photoemission experiments have shown that ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ is a topological insulator. By controlled doping, we have obtained crystals of ${\mathrm{Bi}}_2{\mathrm{Se}}_3$ with nonmetallic conduction. At low temperatures, we uncover a novel type of magnetofingerprint signal which involves the spin degrees of freedom. Given the mm-sized crystals, the observed amplitude is $200–500\times$ larger than expected from universal conductance fluctuations. The results point to very long phase-breaking lengths in an unusual conductance channel in these nonmetallic samples. We discuss the nature of the in-gap conducting states and their relation to the topological surface states.

• Received 9 September 2009

DOI:https://doi.org/10.1103/PhysRevLett.103.246601