Dresden 2014 – wissenschaftliches Programm
O 80.8: Vortrag
Donnerstag, 3. April 2014, 17:45–18:00, GER 38
2PPE measurement on Sb2Te2S with an angle-resolving time-of-flight spectrometer — •Thomas Kunze1, 2, Sophia Ketterl1, Thorsten U. Kampen2, Evgeny Chulkov3, and Martin Weinelt1 — 1FU Berlin, Germany — 2SPECS GmbH, Germany — 3UPV/EHU San Sebastián, Spain
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 kx|| and ky|| 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 n3 dependence. The Dirac cone is populated by indirect filling via the conduction band. The relaxation of the Dirac cone happens on a picosecond timescale.