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Topological insulators (TI) are bulk insulators with topologically protected, electrically conducting surface states. Unfortunately, “practical” topological protection is observed rarely. Interactions between bulk and surface electrons result in surface electrons having short lifetimes and experiencing strong dephasing that impedes possible applications, e.g., in quantum computing.¹ We exploit resonant doping to reduce the bulk carrier concentration to meet the Mott criterion for the metal-insulator transition: the number of electrons due to unintentional doping, n_D, must be less than the critical carrier concentration, n_c; . Se vacancies make Bi₂Se₃ heavily n-type, and the Mott criterion is not reached. By adding resonant dopant Sn to Bi₂Se₃, the density of states is widened at the top of the valence band, decreasing n_c by an order of magnitude, allowing for the Mott criterion to be satisfied.² Seebeck measurements show a sign change for Sn-doped Bi₂Se₃ as temperature is reduced, hinting that this approach works. Further, we plan to add magnetic dopant, Mn, and perform in-field transport measurements.
1. J. Heremans et al., Nat. Rev. Mater. 2 (2017)
2. C. Jaworski et al. PRB 80, 233201 (2009); Wiendlocha, J. Electron. Mater. 45, 3515 (2016)