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

Tracking electron dynamics in graphene and transition metal dichalcogenide

Date Do, 24.11.2016 - Do, 24.11.2016
Time 16:30
Speaker Dr. Céphise Cacho Artemis Central Laser Facility, Rutherford Appleton Laboratory, United Kingdom
Location EPFL CH G1 495, Lausanne
Program Abstract
Novel quantum materials such as graphene and transition metal dichalcogenides (TMDC) are attracting vast interest particularly for their application in spintronic and optoelectronic devices. Their properties are intrinsically governed by the large momentum electrons (at the Brillouin zone K-point). In order to eject such electrons in vacuum and observe their dynamics, a high energy (>20 eV) photon source is required as well as ultrashort pulse duration. High Harmonic Generation source [1] combined to an Angle-Resolved PhotoEmission Spectroscopy (ARPES) end-station is a powerful tool to observe such electron dynamics. After an introduction on ARPES and experimental concepts, I will present an overview of few recent time-resolved ARPES studies performed at the Artemis facility. A quasi-free-standing monolayer of graphene (MLG) is optically excited in a direct interband regime. The measurement of the electronic temperature reveals the role of the supercollisions during the cooling process of the electrons [2]. Over ~100 fs, a population inversion across the Dirac point is observed [3] supporting the potential of graphene for THz amplification applications. Single-layers of MoS2 [4-5], WS2 [6] and bulk WSe2 [7] were resonantly pumped across the band gap at the K point. Measurements of the valence and conduction bands populations give access to the direct quasiparticle band gap [4]. Depending on the screening effects a strong band gap renormalization can be induced [5] by optically excited free charge carriers.
Control of spin- and valley-quantum numbers in valence and conduction bands is achieved [6-7] by using circularly polarized optical excitation.
1. F. Frassetto et al., Optics Express 19, 19169 (2011)
2. J. Johannsen et al., Phys Rev Lett 111, 027403 (2013)
3. I. Gierz et al., Nature Materials 12, 1119 (2013)
4. A. Grubišić Čabo et al., Nano Lett. 15, 5883 (2015)
5. S. Ulstrup et al., ACS Nano 10, 6315 (2016)
6. S. Ulstrup et al., arXiv:1608.06023 (2016)
7. R. Bertoni et al., arXiv:1606.03218 (2016)
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