Quantum pathways of carrier and coherent phonon excitation in bismuth
Azıze Koç, Isabel Gonzalez-Vallejo, Matthias Runge, Ahmed Ghalgaoui, K. Reimann, Laurenz Kremeyer, Fabian Thiemann, M. Horn‐von Hoegen, K. Sokolowski-Tinten, M. Woerner, Thomas Elsaesser
Abstract
Ultrafast mid-infrared excitation of an electron-hole plasma breaks the crystal symmetry of bismuth transiently and opens alternative quantum pathways for the excitation of coherent lattice motions. Probing the transient crystal structure directly by femtosecond x-ray diffraction reveals oscillations of diffracted intensity at a frequency of 2.6 THz, which persist on a picosecond time scale. They reflect coherent wave packet motions along back-folded phonon coordinates in the crystal of reduced symmetry. Optically induced symmetry breaking thus allows for modifying phonon excitations.