  A simple surface band structure and a large bulk band gap have allowed Bi2Se3
to become a reference material for the newly discovered three-dimensional
topological insulators, which exhibit topologically-protected conducting
surface states that reside inside the bulk band gap. Studying topological
insulators such as Bi2Se3 in nanostructures is advantageous because of the high
surface-to-volume ratio, which enhances effects from the surface states;
recently reported Aharonov-Bohm oscillation in topological insulator
nanoribbons by some of us is a good example. Theoretically, introducing
magnetic impurities in topological insulators is predicted to open a small gap
in the surface states by breaking time-reversal symmetry. Here, we present
synthesis of magnetically-doped Bi2Se3 nanoribbons by vapor-liquid-solid growth
using magnetic metal thin films as catalysts. Although the doping concentration
is less than ~ 2%, low-temperature transport measurements of the Fe-doped
Bi2Se3 nanoribbon devices show a clear Kondo effect at temperatures below 30 K,
confirming the presence of magnetic impurities in the Bi2Se3 nanoribbons. The
capability to dope topological insulator nanostructures magnetically opens up
exciting opportunities for spintronics.
