STM/STS studies of a topological insulator

Tetsuo Hanaguri

We have investigated the surface massless Dirac electrons in a topological insulator Bi2Se3 using STM/STS. Under magnetic field perpendicular to the cleaved surface, a series of Landau levels (LLs) has been observed in the tunneling spectra. Remarkably, there is a field-independent LL at the Dirac point, which is a hallmark of Dirac fermions. We developed a scaling analysis scheme of LLs based on the Bohr-Sommerfeld quantization condition which allowed us to determine the energy-momentum dispersion of the surface state. In addition to the LLs, complicated fine peaks appear in the tunneling spectra only in the narrow (+- 20meV) energy window around the Fermi energy. Electronic state becomes spatially inhomogeneous in the same energy range. We speculate that the observed fine peaks are related to the anomalously large amplitude magneto-fingerprint effect.