Berlin 2015 – scientific programme

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TT: Fachverband Tiefe Temperaturen

TT 43: Superconductivity: Fe-based Superconductors – 122

TT 43.6: Talk

Tuesday, March 17, 2015, 15:30–15:45, H 2053

Ultrafast structural dynamics of the Fe-pnictide parent compound BaFe₂As₂ — •L. Rettig¹, S.O. Mariager¹, A. Ferrer^1,2, S. Grübel¹, J.A. Johnson¹, J. Rittmann^1,3, T. Wolf⁴, S.L. Johnson², G. Ingold¹, P. Beaud¹, and U. Staub¹ — ¹Paul Scherrer Institut, CH-5232 Villigen PSI, Switzerland — ²ETH Zürich, CH-8093 Zürich, Switzerland — ³EPFL, CH-1015 Lausanne, Switzerland — ⁴KIT, D-76021 Karlsruhe, Germany

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 Fe pnictides, especially the strong sensitivity of the electronic and magnetic properties to the Fe-As tetrahedra angle plays a crucial role for superconductivity and demonstrates a strong magneto-structural coupling.

Here, we use femtosecond time-resolved x-ray diffraction to investigate the structural dynamics in the Fe-pnictide parent compound BaFe₂As₂. We observe fluence dependent intensity oscillations of two specific Bragg reflections. Their distinctly different sensitivity to the pnictogen height demonstrates the coherent excitation of the A_1g 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 an ultrafast increase of the Fe magnetic moments.