Effect of spin-polarized electrons on terahertz emission from photoexcited GaAs

Abstract

The influence of elliptically and circularly polarized excitation on terahertz emission from unbiased bulk GaAs at normal incidence and room temperature is reported. Illumination of GaAs above the bandgap produces both spin-polarized electrons and shift currents. The induced currents are monitored via terahertz emission spectroscopy. The terahertz emission amplitude is compared to theoretical calculations as a function of excitation beam ellipticity. Exciting slightly above the bandgap ͑800 nm at room temperature͒ with elliptical polarization generates shift currents that deviate substantially from theoretical predictions. On the other hand, exciting either below the bandgap ͑835 nm at 77 K͒ to produce optical rectification or far above the bandgap ͑400 nm at room temperature͒ to produce shift currents generates emission in agreement with theoretical calculations. Spin-polarized electrons created by elliptically polarized excitation are the source of the observed discrepancy.

Coherent ultrafast spin-dynamics probed in three dimensional topological insulators

“…By relating these transitions to the element projected band structure (see Supplementary Materials ), we can interpret them as rectification and shift currents 34 35 . While the first one results in a diffusive current with different velocities of the spin-polarized excited carriers, the other results in a replacement of charge (spin polarized) in the unit cell and a short polarization.…”

Influence of free-carrier absorption on terahertz generation from ZnTe(110)

“…When detecting in the far-field, 17 terahertz radiation due to shift currents has a waveform that follows the first time-derivative of the time-varying excitation pulse intensity, while rectification currents produce terahertz radiation having a waveform that is the second time derivative. Experiments carried out by Cote et al 22 and more recently by Schleicher et al 19 have experimentally verified this time-derivative relationship between terahertz radiation generated by shift currents and optical rectification in GaAs.…”

“…At excitation fluences below 17 J / cm 2 , the time-dependence of the terahertz waveform resembles the second derivative of the Gaussian excitation pulse, which is the shape expected for optical rectification with detection in the far field. [17][18][19] At higher fluences, however, the waveform is noticeably attenuated at later times and more closely resembles the first derivative of the Gaussian excitation pulse. The filled circles in part ͑b͒ show that the terahertz amplitude varies linearly with excitation fluences below 17 J / cm 2 as expected for optical rectification but is sublinear above 33 J / cm 2 .…”

Spin‐Polarized Electrons Impact on Terahertz Emission by High‐Order Shift Current in CsPbBr3

“…When it is excited by LPL, the densities of spin-polarized electrons for both spin-up and spin-down electrons are equal. [44] The density of the spin-up electrons (n ↑ ) and spindown (n ↓ ) are in direct proportion to the TPA coefficients β + and β − , respectively. Therefore, the electron densities under RCPL and LCPL are lower than the free electron density under LPL excitation (n l ∝β l ) because of the different twophoton selection rules.…”