Electron spin resonance of GD3+ in three dimensional topological insulator BI2SE3

Abstract

Bi2Se3 has been claimed to be a three dimensional topological insulator (TI) with topologically protected metallic surface states with exotic properties. We have performed electron spin resonance (ESR) measurements on Gd3+ doped (x approximate to 0.01) Bi2Se3 single crystal grown from stoichiometric melt. For the studied crystals, our preliminary results revealed a partly resolved Gd3+ fine structure spectrum with Dysonian (metallic character) lines. At room temperature, the central line has a g approximate to 1.98, a linewidth Delta H approximate to 95 G and the spectra have a overall splitting of roughly 1300 Oe. As the temperature is decreased, the Gd3+ ESR Delta H of the central line presents a very small Korringa-like behavior b = Delta H/Delta T approximate to 0.013 Oe/K and nearly T-independent g-value. However, for T less than or similar to 40 K, Delta H shows a stronger narrowing effect evolving to Korringa-like behavior (b approximate to 0.15 Oe/K) for T less than or similar to 30 K. Concomitantly with the change in Delta H behavior, the Gd3+ central line g value starts to decrease reaching a value of 1.976 at T less than or similar to 4.2 K. The ESR results are discussed in terms of possible effects of protected topological surface states enlightened by complementary data from macroscopic measurements