Fig. S7.

NMR T₁ and Knight shift study of metallic surface states in (Bi₂Te₃)_x(Sb₂Te₃)_1-x. (A) ¹²¹Sb and ¹²⁵Te NMR spin-lattice relaxation rates (1/T₁) of bulk and nanoscale (Bi₂Te₃)_x(Sb₂Te₃)_1-x as a function of temperature. The Korringa relation holds over the entire temperature range for nanoscale samples of (Bi₂Te₃)_x(Sb₂Te₃)_1-x, as shown by the red thick lines. (B) A typical relaxation curve is shown (¹²¹Sb nuclear spin magnetization at 160 K and 7.05 T versus time). (C) In the bulk of these materials, the Korringa law does not hold. Instead, a thermally activated process related to their semiconducting behavior is apparent.