69 research outputs found
Symmetry breaking as the origin of zero-differential resistance states of a 2DEG in strong magnetic fields
Zero resistance differential states have been observed in two-dimensional
electron gases (2DEG) subject to a magnetic field and a strong dc current. In a
recent work we presented a model to describe the nonlinear transport regime of
this phenomenon. From the analysis of the differential resistivity and the
longitudinal voltage we predicted the formation of negative differential
resistivity states, although these states are known to be unstable. Based on
our model, we derive an analytical approximated expression for the
Voltage-Current characteristics, that captures the main elements of the
problem. The result allow us to construct an energy functional for the system.
In the zero temperature limit, the system presents a quantum phase transition,
with the control parameter given by the magnetic field. It is noted that above
a threshold value (), the symmetry is spontaneously broken. At
sufficiently high magnetic field and low temperature the model predicts a phase
with a non-vanishing permanent current; this is a novel phase that has not been
observed so far.Comment: 6 pages, 2 figure
Giant spin-dependent photo-conductivity in GaAsN dilute nitride semiconductor
A theoretical and experimental study of the spin-dependent photoconductivity
in dilute Nitride GaAsN is presented. The non linear transport model we develop
here is based on the rate equations for electrons, holes, deep paramagnetic and
non paramagnetic centers both under CW and pulsed optical excitation. Emphasis
is given to the effect of the competition between paramagnetic centers and non
paramagnetic centers which allows us to reproduce the measured characteristics
of the spin-dependent recombination power dependence. Particular attention is
paid to the role of an external magnetic field in Voigt geometry. The
photoconductivity exhibits a Hanle-type curve whereas the spin polarization of
electrons shows two superimposed Lorentzian curves with different widths,
respectively related to the recombination of free and trapped electrons. The
model is capable of reproducing qualitatively and quantitatively the most
important features of photoluminescence and photocurrent experiments and is
helpful in providing insight on the various mechanisms involved in the electron
spin polarization and filtering in GaAsN semiconductors.Comment: 10 pages, 5 figure
Room temperature Giant Spin-dependent Photoconductivity in dilute nitride semiconductors
By combining optical spin injection techniques with transport spectroscopy
tools, we demonstrate a spin-photodetector allowing for the electrical
measurement and active filtering of conduction band electron spin at room
temperature in a non-magnetic GaAsN semiconductor structure. By switching the
polarization of the incident light from linear to circular, we observe a Giant
Spin-dependent Photoconductivity (GSP) reaching up to 40 % without the need of
an external magnetic field. We show that the GSP is due to a very efficient
spin filtering effect of conduction band electrons on Nitrogen-induced Ga
self-interstitial deep paramagnetic centers.Comment: 4 pages, 3 figure
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