Forthcoming Events

07.06.2022 - 10.06.2022, Grindelwald, Switzerland
20.06.2022 - 23.06.2022, SLAC National Accelerator Laboratory
27.06.2022 - 29.06.2022, University College London, UK

News

New scientific highlight- by MUST PI 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
Kick-Off dynaMENT Mentoring for Women in Natural Sciences- with Ursula Keller as plenary speaker
Four new scientific highlights- by MUST PIs Chergui / Milne / Beaud / Staub, by Wolf / Röthlisberger, by Wörner, and Keller

Understanding the interplay of electrons, spins and lattice is essential for many complex materials, including the high-temperature superconductors

February 13, 2015
 

Ultrafast Structural Dynamics of the Fe-Pnictide Parent Compound BaFe2As2


Understanding the interplay of the various degrees of freedom such as the electrons, spins and lattice is essential for many complex materials, including the high-temperature superconductors. In the case of the Fe pnictides, especially the strong sensitivity of the electronic and magnetic properties to the exact shape and size of the Fe-As tetrahedra (Fig. 1, left) plays a crucial role for superconductivity and demonstrates a strong magneto-structural coupling. In addition, antiferromagnetic phases are closely linked to structural distortions in these materials.
Here, we use femtosecond time-resolved x-ray diffraction at FEMTO to investigate the structural dynamics in the Fe-pnictide parent compound BaFe2As2. We observe fluence dependent intensity oscillations of two specific Bragg reflections with a period of ~200 fs (Fig. 1, right). Their distinctly different sensitivity to the pnictogen height h demonstrates the coherent excitation of the A1𝑔 phonon mode and allows us to quantify the coherent modifications of the Fe-As tetrahedra. By a comparison with time-resolved photoemission data we derive the electron-phonon deformation potential for this particular mode, which is comparable to theoretical predictions. Our results demonstrate the importance of this structural degree of freedom for the electron-phonon coupling in the Fe pnictides and indicate a transient increase of the Fe magnetic moments on an ultrafast timescale.
In addition, in the spin-density wave ground state we investigate the reduction of the orthorhombic distortion by the laser excitation. The orthorhombic splitting of the Bragg reduces on a timescale of several tens of picoseconds, compatible with domain motion. This contrasts with the ultrafast quench of the magnetic ordering in <200 fs and provides further information about the coupling of magnetic and structural degrees of freedom.



Figure 1. Top: Pump-induced change of diffraction intensity of the (1 0 5) reflection. Bottom: Structure of BaFe2As2 with the motion pattern of the A1g phonon mode (red arrows).

Reference: Rettig, L, S O Mariager, A Ferrer, S Grübel, J A Johnson, J Rittmann, T Wolf, S L Johnson, G Ingold, P Beaud, and U Staub, Ultrafast Structural Dynamics of the Fe- Pnictide Parent Compound BaFe2As2. Phys. Rev. Lett., (2015) 114: 067402 (10.1103/PhysRevLett.114.067402) Rettig-2015

back <<
NCCR MUST Office : ETHZ IQE/ULP-HPT H3 | Auguste-Piccard-Hof 1 | 8093 Zurich | E-Mail | +41 44 633 36 02
The National Centres of Competence in Research (NCCR) are a research instrument of the Swiss National Science Foundation
FNSNF