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Sum-rule constraints on the surface state conductance of topological insulators.

  • Author(s): Post, KW
  • Chapler, BC
  • Liu, MK
  • Wu, JS
  • Stinson, HT
  • Goldflam, MD
  • Richardella, AR
  • Lee, JS
  • Reijnders, AA
  • Burch, KS
  • Fogler, MM
  • Samarth, N
  • Basov, DN
  • et al.
Abstract

We report the Drude oscillator strength D and the magnitude of the bulk band gap E_{g} of the epitaxially grown, topological insulator (Bi,Sb)_{2}Te_{3}. The magnitude of E_{g}, in conjunction with the model independent f-sum rule, allows us to establish an upper bound for the magnitude of D expected in a typical Dirac-like system composed of linear bands. The experimentally observed D is found to be at or below this theoretical upper bound, demonstrating the effectiveness of alloying in eliminating bulk charge carriers. Moreover, direct comparison of the measured D to magnetoresistance measurements of the same sample supports assignment of the observed low-energy conduction to topological surface states.

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