Magnetically doped semiconducting topological insulators

The time invariant behaviors of topological insulators are expected to be changed with magnetic doping, which motivate the present study. Here, we show that for Bi _2-xCr _xSe ₃ (0.01 ≤ x ≤ 0.3) thin films grown on Si, the non-trivial topological surface state is weakened by the Cr dopants. The band gap of surface is opened and monotonically increased with Cr concentration up to ∼100 meV at ∼ 10 K. Meanwhile, the semiconducting behavior is well-maintained in the bulk owing to the reduction of background doping by means of a modified growth strategy and an in situ passivation method. Besides, we also observe the existence of unconventional ferromagnetic ordering below 35 K, for which the Curie-Weiss Law and conventional/modified Arrott equations do not apply. These observations may further help us investigate extraordinary magneto-electric effect in topological insulators, and the result will also pave the way for realizing the quantized anomalous Hall effect.