Forthcoming Events

05.09.2022 - 09.09.2022, Iseolago hotel, Iseo, Italy.


MUST2022 Conference- a great success!
New scientific highlights- by MUST PIs Wörner, Chergui, and Richardson
FELs of Europe prize for Jeremy Rouxel- “Development or innovative use of advanced instrumentation in the field of FELs”
Ruth Signorell wins Doron prizefor pioneering contributions to the field of fundamental aerosol science
New FAST-Fellow Uwe Thumm at ETH- lectures on Topics in Femto- and Attosecond Science
International Day of Women and Girls in Science- SSPh asked female scientists about their experiences
New scientific highlight- by MUST PIs Milne, Standfuss and Schertler
EU XFEL Young Scientist Award for Camila Bacellar,beamline scientist and group leader of the Alvra endstation at SwissFEL
Prizes for Giulia Mancini and Rebeca Gomez CastilloICO/IUPAP Young Scientist Prize in Optics & Ernst Haber 2021
Nobel Prize in Chemistry awarded to RESOLV Member Benjamin List- for the development of asymmetric organocatalysis
NCCR MUST at Scientifica 2021- Lightning, organic solar cells, and virtual molecules
#NCCRWomen- NCCR MUST celebrates 50 years women’s right to vote in Switzerland

LACUS Event: Ultrafast electronic band gap control and inhibition of the photoinduced structural phase transition in an excitonic insulator

Date Fr, 15.06.2018 - Fr, 15.06.2018
Time 11.00
Speaker Selen Mor, Fritz-Haber-Institut der Max-Planck-Gesellschaft, Germany
Location EPFL, Building CH G1495
Program Abstract:
Ultrafast control of matter phases is of both fundamental and technological interest. Here, we study the ultrafast dynamics of Ta 2 NiSe 5 by means of time- and angle-resolved photoelectron spectroscopy (trARPES) [1] and transient reflectivity measurements [2]. Ta 2 NiSe 5 is proposed to support an excitonic insulator (EI) phase below T C ≈ 328 K, combined with a structural change from orthorombic to monoclinic symmetry. 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. Below T C, trARPES around  shows a strong fluence-dependent valence band depopulation, until absorption saturates at a critical fluence F sat = 0.2 mJ cm −2 . This is reflected in a saturation of the mid-IR optical response at F sat . A coherent phonon at 4 THz, marker of the EI/monoclinic phase, persists above T C , indicating that the photoinduced structural transition is hindered by pump absorption saturation. trARPES shows that below F sat the band gap shrinks transiently due to photoenhanced screening of the Coulomb interaction, while above F sat it widens and recovers to its equilibrium value after ~1.5 ps. Hartree-Fock calculations reveal that the band gap widening is due to photoenhancement of the exciton condensate, persisting until the system undergoes interband relaxation. Our results prove it is possible to manipulate exciton condensates optically and gain ultrafast control of semiconductor band gaps.

[1] Mor et al., Phys. Rev. Lett. 119, 086401 (2017).
Download (75 KB)
(75 KB)
NCCR MUST Office : ETHZ IQE/ULP-HPT H3 | Auguste-Piccard-Hof 1 | 8093 Zurich | E-Mail
The National Centres of Competence in Research (NCCR) are a research instrument of the Swiss National Science Foundation