Speaker
Description
We present two-photon photoemission measurements on the p-doped
topological insulator Sb2Te2S. The Dirac cone of this system lies
above the Fermi energy and is therefore only accessible using
two-photon photoemission.
We detect the photoemitted electrons with an angle-resolving
time-of-flight spectrometer. This instrument allows us to measure
the kinetic energy E as a function of both k directions without
rotating the sample. Our laser system with two OPAs gives us the
opportunity to tune the photon energy of the infrared and
ultraviolet pulse independently. This allows us to create a
resonant population and efficient probing of the Dirac cone.
Sb2Te2S shows a Dirac cone with direction-dependent linear
dispersion close above the Fermi level and hexagonal warping at
higher energies. Polarization-dependent measurements manifest the
spin texture of the Dirac cone.
The population dynamics of Sb2Te2S have been analyzed. The femtosecond lifetimes of the first and second image-potential states show an n^3 dependence. The Dirac cone is populated by indirect filling via the conduction band. Therelaxation of the Dirac cone happens on a picosecond timescale.
