Spectroscopic perspective on the interplay between electronic and magnetic properties of magnetically doped topological insulators

Abstract

The quantum anomalous Hall (QAH) effect involves spin-polarized, dissipation-free chiral edge state transport in the absence of an external magnetic field. This effect has been realized in magnetically doped topological insulators, such as Cr- and V-doped (Bi,Sb)${}_{2}$Te${}_{3}$ thin films. To date, the observation of the QAH effect in these materials is limited to millikelvin temperatures deep below their ferromagnetic transition temperature. In this report, the authors provide complementary magnetic and electronic study of such systems using muon spin and photoemission spectroscopies. They show that the topological insulator layers become fully ferromagnetic only at much lower temperature than the onset temperature for ferromagnetism and demonstrate the presence of a magnetic impurity band with a finite density of states at the Fermi level. Both properties may be responsible for the low temperature needed for observing the QAH effect.