title: Sum-rule constraints on the surface state conductance of topological insulators.
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.
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, California 92093, USA.
authors.forename: K W
authors.initials: KW
authors.lastname: Post
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, California 92093, USA.
authors.forename: B C
authors.initials: BC
authors.lastname: Chapler
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, California 92093, USA.
authors.forename: M K
authors.initials: MK
authors.lastname: Liu
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, California 92093, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Wu
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, California 92093, USA.
authors.forename: H T
authors.initials: HT
authors.lastname: Stinson
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, California 92093, USA.
authors.forename: M D
authors.initials: MD
authors.lastname: Goldflam
authors.affiliation: Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: A R
authors.initials: AR
authors.lastname: Richardella
authors.affiliation: Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: J S
authors.initials: JS
authors.lastname: Lee
authors.affiliation: Department of Physics & Institute for Optical Sciences, University of Toronto, Toronto, Ontario M5S 1A7, Canada.
authors.forename: A A
authors.initials: AA
authors.lastname: Reijnders
authors.affiliation: Department of Physics, Boston College, Chestnut Hill, Massachusetts 02467, USA.
authors.forename: K S
authors.initials: KS
authors.lastname: Burch
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, California 92093, USA.
authors.forename: M M
authors.initials: MM
authors.lastname: Fogler
authors.affiliation: Department of Physics, The Pennsylvania State University, University Park, Pennsylvania 16802, USA.
authors.forename: N
authors.initials: N
authors.lastname: Samarth
authors.affiliation: Physics Department, University of California-San Diego, La Jolla, California 92093, USA.
authors.forename: D N
authors.initials: DN
authors.lastname: Basov