Dresden 2017 – scientific programme
Parts | Days | Selection | Search | Updates | Downloads | Help
O: Fachverband Oberflächenphysik
O 75: Ultrafast Electron and Spin Dynamics
O 75.1: Talk
Wednesday, March 22, 2017, 15:00–15:15, TRE Phy
Ultrafast electronic band gap control in an excitonic insulator — •Selene Mor1, Marc Herzog2, Denis Golez3, Philipp Werner3, Martin Eckstein4, Claude Monney5, and Julia Stähler1 — 1Fritz-Haber-Institut, Berlin, Germany — 2Potsdam Univ., Potsdam, Germany — 3Fribourg Univ., Fribourg, Switzerland — 4MPG for Structural Dynamics, Hamburg, Germany — 5Zurich Univ., Zurich, Switzerland
Ultrafast control of material properties is of both fundamental and technological interest. Here, we investigated the sub-picosecond dynamics of the electronic structure of Ta2NiSe5 by means of time- and angle-resolved photoelectron spectroscopy (trARPES). The system was proposed to support an excitonic insulator (EI) phase below Tc≈ 328 K. Such an EI phase is expected to occur in small gap semiconductors with strong electron-hole interaction as excitons can form spontaneously and condense into a ground state with a larger gap. trARPES below Tc reveals a strong excitation-density-dependent valence band depopulation, until absorption saturates at a critical fluence FC = 0.2 mJ cm−2. Below FC the band gap shrinks transiently due to photoenhanced screening of Coulomb interaction, while it widens above FC for and relaxes after ≈ 1.5 ps. Hartree-Fock calculations reveal that the band gap widening can be explained by photoenhancement of the density of the exciton condensate, an effect that persists until the system undergoes interband relaxation. These results prove the possibility to manipulate condensates of excitons with light and to gain ultrafast control of the size of semiconductor band gaps.