207 research outputs found
Layer interdependence of transport in an undoped electron-hole bilayer
The layer interdependence of transport in an undoped electron-hole bilayer
(uEHBL) device was studied as a function of carrier density, interlayer
electric field, and temperature. The uEHBL device consisted of a density
tunable, independently contacted two-dimensional electron gas (2DEG) and
two-dimensional hole gas (2DHG) induced via field effect in distinct GaAs
quantum wells separated by a 30 nm AlGaAs barrier. Transport
measurements were made simultaneously on each layer using the van der Pauw
method. An increase in 2DHG mobility with increasing 2DEG density was observed,
while the 2DEG mobility showed negligible dependence on the 2DHG density.
Decreasing the interlayer electric-field and thereby increasing interlayer
separation also increased the 2DHG mobility with negligible effects on the 2DEG
mobility. The change in interlayer separation as interlayer electric-field
changed was estimated using 2DHG Coulomb drag measurements. The results were
consistent with mobility of each layer being only indirectly dependent on the
adjacent layer density and dominated by background impurity scattering.
Temperature dependencies were also determined for the resistivity of each
layer.Comment: 8 pages, 6 figures, submitted to Phys. Rev.
Superradiant Decay of Cyclotron Resonance of Two-Dimensional Electron Gases
We report on the observation of collective radiative decay, or superradiance,
of cyclotron resonance (CR) in high-mobility two-dimensional electron gases in
GaAs quantum wells using time-domain terahertz magnetospectroscopy. The decay
rate of coherent CR oscillations increases linearly with the electron density
in a wide range, which is a hallmark of superradiant damping. Our fully quantum
mechanical theory provides a universal formula for the decay rate, which
reproduces our experimental data without any adjustable parameter. These
results firmly establish the many-body nature of CR decoherence in this system,
despite the fact that the CR frequency is immune to electron-electron
interactions due to Kohn's theorem.Comment: 5 pages, 4 figure
Highly efficient terahertz photoconductive metasurface detectors operating at microwatt-level gate powers
Despite their wide use in terahertz (THz) research and technology, the application spectra of photoconductive antenna (PCA) THz detectors are severely limited due to the relatively high optical gating power requirement. This originates from poor conversion efficiency of optical gate beam photons to photocurrent in materials with subpicosecond carrier lifetimes. Here we show that using an ultra-thin (160 nm), perfectly absorbing low-temperature grown GaAs metasurface as the photoconductive channel drastically improves the efficiency of THz PCA detectors. This is achieved through perfect absorption of the gate beam in a significantly reduced photoconductive volume, enabled by the metasurface. This Letter demonstrates that sensitive THz PCA detection is possible using optical gate powers as low as 5 μW-three orders of magnitude lower than gating powers used for conventionalPCAdetectors.We show that significantly higher optical gate powers are not necessary for optimal operation, as they do not improve the sensitivity to the THz field. This class of efficient PCA THz detectors opens doors for THz applications with low gate power requirements
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