"Resonant magneto-optic Kerr effect in the magnetic topological insulator Cr:(Sbx,Bi1−x)2Te3"

Shreyas Patankar: J. P. Hinton, Joel Griesmar, J. Orenstein, J. S. Dodge, Xufeng Kou, Lei Pan, Kang L. Wang, A. J. Bestwick, E. J. Fox, D. Goldhaber-Gordon, Jing Wang, and Shou-Cheng Zhang; Physical Review B, 12/31/15.

Additional Authors: J. P. Hinton, Joel Griesmar, J. Orenstein, J. S. Dodge, Xufeng Kou, Lei Pan, Kang L. Wang, A. J. Bestwick, E. J. Fox, D. Goldhaber-Gordon, Jing Wang, and Shou-Cheng Zhang

Abstract:

We report measurements of the polar Kerr effect, proportional to the out-of-plane component of the magnetization, in thin films of the magnetically doped topological insulator (Cr0.12Bi0.26Sb0.62)2Te3. Measurements of the complex Kerr angle ΘK were performed as a function of photon energy in the range 0.8eV<ℏω<3.0eV. We observed a peak in the real part of ΘK(ω) and zero crossing in the imaginary part that we attribute to a resonant interaction with a spin-orbit avoided crossing located ≈1.6 eV above the Fermi energy. The resonant enhancement allows measurement of the temperature and magnetic field dependence of ΘK in the ultrathin film limit, d≥2 quintuple layers (QL). We find a sharp transition to zero remanent magnetization at 6 K for d<8 QL, consistent with theories of the dependence of impurity spin interactions on film thickness and their location relative to topological insulator surfaces.