Regensburg 2025 – scientific programme

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HL: Fachverband Halbleiterphysik

HL 61: THz and MIR physics in semiconductors

HL 61.4: Talk

Friday, March 21, 2025, 11:30–11:45, H14

Unraveling the Microscopic Mechanism of Displacive Excitation of Coherent Phonons in a Bulk Rashba Semiconductor — •Peter Fischer¹, Julian Bär¹, Moritz Cimander¹, Volker Wiechert¹, Oleg Tereshchenko², and Davide Bossini¹ — ¹Department of Physics and Center for Applied Photonics, University of Konstanz, D-78457 Konstanz, Germany — ²Nowosibirsk, Russia

Optically driven lattice excitations have recently been intensively investigated as a means to manipulate the macroscopic properties of quantum materials. In solids with an electronic band gap, it is well-established that coherent phonons can be excited by laser pulses with photon energies exceeding the band-gap energy. However, the dominant microscopic mechanism has still not been pinpointed: Neither experimentally nor theoretically has it been possible to disentangle the effect of a photo-induced change in the charge-carrier density from an increase of the carrier temperature. We perform time-resolved pump-probe spectroscopy on the Rashba semiconductor BiTeI. Tuning the pump-photon energy from the visible to the mid-infrared allows us to excite both interband and barely accessible intraband transitions. As a result, we determine that the lattice modes are mainly driven by the increased carrier temperature. In addition, the phonon coherence time in the intraband regime proves robust against an increase in laser fluence. These findings provide new insights for the development of schemes addressing the coherent structural manipulation of solids.

Keywords: Coherent Phononics; Time-resolved Pump-Probe Experiment; Time-Domain Spectroscpy; Rashba Effect