Orbital selective dynamics in Fe-pnictides triggered by polarized pump pulse excitations

¹ Laboratory of Quantum Optics, University of Nova Gorica - 5001 Nova Gorica, Slovenia
² Elettra-Sincrotrone Trieste, Area Science Park - 34149 Trieste, Italy
³ Department of Condensed Matter Physics and Materials Science, Tata Institute of Fundamental Research Homi Bhabha Road, Colaba, Mumbai-400005, India

^(a) ganesh.adhikary@gmail.com
^(b) giovanni.de.ninno@ung.si
^(c) kbmaiti@tifr.res.in (corresponding author)

Received: 23 May 2021
Accepted: 7 October 2021

Abstract

Quantum materials display exotic behaviours related to the interplay between temperature-driven phase transitions. Here, we study the electron dynamics in one such material, CaFe₂As₂, a parent Fe-based superconductor, employing time- and angle-resolved photoemission spectroscopy. CaFe₂As₂ exhibits concomitant transition to spin density wave state and tetragonal to orthorhombic structure below 170 K. The Fermi surface of this material consists of three hole pockets ?, β and ? around the Γ-point and two electron pockets around the X-point. The hole pockets have d_xy, d_yz and d_zx orbital symmetries. The β band constituted by d_xz/d_yz orbitals exhibits a gap across the magnetic phase transition. We discover that polarized pump pulses can induce excitations of electrons of a selected symmetry. More specifically, while s-polarized light (polarization vector perpendicular to the xz plane) excites electrons corresponding to all the three hole bands, p-polarized light excites electrons essentially from ?,β bands which are responsible for magnetic order. Interestingly, within the magnetically ordered phase, the excitation due to the p-polarized pump pulses occur at a time scale of 50 fs, which is significantly faster than the excitation induced by s-polarized light (∼200 fs). These results suggest that the relaxation of different ordered phases occurs at different time scales and this method can be used to achieve selective excitations to disentangle complexity in the study of quantum materials.