Ghalgaoui Ahmed, Reimann Klaus, Woerner Michael, Elsaesser Thomas, Flytzanis Christos, Biermann Klaus
Max-Born-Institut für Nichtlineare Optik und Kurzzeitspektroskopie, 12489 Berlin, Germany.
Laboratoire de Physique, École Normale Supérieure, Université PSL, 75231 Paris, France.
Phys Rev Lett. 2020 Jul 10;125(2):027401. doi: 10.1103/PhysRevLett.125.027401.
The impact of transient electric currents on the transverse optical (TO) phonon resonance is studied after excitation by two femtosecond near-infrared pulses via the fourth-order nonlinear terahertz emission. Nonlinear signals due to interband shift currents and heavy-hole-light-hole polarizations are separated from Raman-induced TO phonon coherences. The latter display a frequency upshift by some 100 GHz upon interband excitation of an electron-hole plasma. The frequency shift is caused by transverse electronic shift currents, which modify the dielectric function. A local-field model based on microscopic current densities reproduces the observed frequency upshift.
