Terahertz Kerr and reflectivity measurements on the topological insulator Bi2Se3

We report the first terahertz Kerr measurements on bulk crystals of the topological insulator Bi2Se3. At T = 10 K and fields up to 8 T, the real and imaginary Kerr angle and reflectance measurements utilizing both linearly and circularly polarized incident radiation were measured at a frequency of 5.24 meV. A single fluid free carrier bulk response cannot describe the line shape. Data from one sample is quantitatively described by a surface state with a small mass and surprisingly large associated spectral weight. However, an alternative interpretation in terms of bulk carrier-density variations remains a possibility