Realizing Giant Magneto-Optical Effects in 3D Topological Insulators Without Magnetic Fields

Topological insulators display unusual light-matter interactions due to the helical nature of surface electronic states. We study the near-field interaction of light propagating in an optical fiber with crystals of Sb2Te3, a 3D topological insulator (TI), and observe a large apparent Faraday rotation. The origin of this unexpected polarization rotation in the optical fiber is attributed to a magneto-optical Kerr effect at the TI-fiber interface. We show that the combined effects of time-reversal symmetry breaking, which arises from Zeeman coupling of the electromagnetic field with the surface electrons of the TI, and inversion symmetry breaking of optical excitations, which arises from the exponential decay of the evanescent light across the TI crystal, are central to realizing this giant polarization rotation. Our work demonstrates a facile approach for realizing large magneto-optical effects without any magnetic fields by exploiting the unique physics of light-matter interactions at TI surfaces.