143 research outputs found
Terahertz magneto-spectroscopy of transient plasmas in semiconductors
Using synchronized near-infrared (NIR) and terahertz (THz) lasers, we have
performed picosecond time-resolved THz spectroscopy of transient carriers in
semiconductors. Specifically, we measured the temporal evolution of THz
transmission and reflectivity after NIR excitation. We systematically
investigated transient carrier relaxation in GaAs and InSb with varying NIR
intensities and magnetic fields. Using this information, we were able to
determine the evolution of the THz absorption to study the dynamics of
photocreated carriers. We developed a theory based on a Drude conductivity with
time-dependent density and density-dependent scattering lifetime, which
successfully reproduced the observed plasma dynamics. Detailed comparison
between experimental and theoretical results revealed a linear dependence of
the scattering frequency on density, which suggests that electron-electron
scattering is the dominant scattering mechanism for determining the scattering
time. In InSb, plasma dynamics was dramatically modified by the application of
a magnetic field, showing rich magneto-reflection spectra, while GaAs did not
show any significant magnetic field dependence. We attribute this to the small
effective masses of the carriers in InSb compared to GaAs, which made the
plasma, cyclotron, and photon energies all comparable in the density, magnetic
field, and wavelength ranges of the current study.Comment: 8 pages, 9 figures, submitted to Phys. Rev.
A classical model for the negative dc conductivity of ac-driven 2D electrons near the cyclotron resonance
A classical model for {\em dc} transport of two dimensional electrons in a
perpendicular magnetic field and under strong irradiation is considered. We
demonstrate that, near the cyclotron resonance condition, and for {\em linear}
polarization of the {\em ac} field, a strong change of the diagonal component,
, of the {\em dc} conductivity occurs in the presence of a {\em weak}
nonparabolicity of the electron spectrum. Small change in the electron
effective mass due to irradiation can lead to negative , while the
Hall component of the {\em dc} conductivity remains practically unchanged.
Within the model considered, the sign of depends on the relative
orientation of the {\em dc} and {\em ac} fields, the sign of the detuning of
the {\em ac} frequency from the cyclotron resonance, and the sign of
nonparabolic term in the energy spectrum.Comment: 4 pages, 1 figur
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