Magneto-transport and Kondo effect in cobalt doped Bi_2Se_3 topological insulators

摘要

Weak magnetic perturbation on the surface of topological insulators breaks the time reversal symmetry and opens the energy gap. We report the effect of cobalt doping in Bi_2Se_3 single crystals grown by the modified Bridgeman technique. The magnetic susceptibility of the cobalt doped Bi_2Se_3 changes from diamagnetic to paramagnetic at room temperature and then to ferromagnetic at 2K. The Kondo effect was observed in bulk crystals for Bi_(1.8)Co_(0.2)Se_3 (i.e., 10% Co doped in Bi_2Se_3), whereas the lower doping of cobalt results in a simple metallic behavior. In order to study the surface properties, the devices were fabricated on mechanically exfoliated thin (～70 nm) flakes of Bi_(1.8)Co_(0.2)Se_3 obtained from the bulk crystal. Semiconducting behavior can be clearly seen in Bi_(1.8)Co_(0.2)Se_3 devices at T＞40K, and the Kondo effect was observed when the temperature was below 40 K. In the Bi_(1.8)Co_(0.2)Se_3 device, the weak antilocalization to weak localization transition observed in magnetoresistance behavior at T ～ 40 K indicates the band opening at the Dirac point.