Dresden 2014 – scientific programme

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O: Fachverband Oberflächenphysik

O 80: Surface Dynamics I

O 80.8: Talk

Thursday, April 3, 2014, 17:45–18:00, GER 38

2PPE measurement on Sb₂Te₂S with an angle-resolving time-of-flight spectrometer — •Thomas Kunze^{1, 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 k_x|| and k_y|| 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.