41 research outputs found
Absolute negative conductivity in two-dimensional electron systems under microwave radiation
We overview mechanisms of absolute negative conductivity in two-dimensional
electron systems in a magnetic field irradiated with microwaves and provide
plausible explanations of the features observed in recent experiments related
to the so-called zero-resistance (zero-conductance) states.Comment: 4 pages, 7 figures, presented at Internat. Symp. on Functional
Semiconductor Nanosystems, Atsugi, Japan, Nov. 12-14, 2003, be published in
Physica
Pseudo-gap and spin polarization in a two-dimensional electron gas
Tunnelling density of states in the vicinity of Fermi level of a
two-dimensional electron gas subjected to an external parallel and zeroth
magnetic field is calculated. It reveals a pseudo-gap recently observed in the
experiments. The gap originates in spin polarization of 2DEG. Non-monotonic
dependence of energy on a Landau level filling factor (density) was obtained.
It implies the tunneling current peculiarities at filling factors 1/2 and 1.
The Ising-like model of the exchange interaction in 2DEG was exploited instead
of the conventional one. It was crucial to achieve even a qualitative agreement
with experimental data.Comment: 6 pages, 3 figure; corrected typos, improved figure
Effect of heating and cooling of photogenerated electron-hole plasma in optically pumped graphene on population inversion
We study the characteristics of photogenerated electron-hole plasma in
optically pumped graphene layers at elevated (room) temperatures when the
interband and intraband processes of emission and absorption of optical phonons
play a crucial role. The electron-hole plasma heating and cooling as well as
the effect of nonequilibrium optical phonons are taken into account. % The
dependences of the quasi-Fermi energy and effective temperature of optically
pumped graphene layers on the intensity of pumping radiation are calculated.
The variation of the frequency dependences dynamic conductivity with increasing
pumping intensity as well as the conditions when this conductivity becomes
negative in a certain range of frequencies are considered. %
The effects under consideration can markedly influence the achievement of the
negative dynamic conductivity in optically pumped graphene layers associated
with the population inversion and, hence, the realization graphene-based
terahertz and infrared lasers operating at room temperatures.Comment: 12 pages, 7 figure
Current-voltage characteristics of a graphene nanoribbon field-effect transistor
We present an analytical device model for a field-effect transistor based on
a heterostructure which consists of an array of nanoribbons clad between the
highly conducting substrate (the back gate) and the top gate controlling the
source-drain current. The equations of the model of a graphene nanoribbon
field-effect transistor (GNR-FET) include the Poisson equation in the weak
nonlocality approximation. Using this model, we find explicit analytical
formulas for the spatial distributions of the electric potential along the
channel and for the GNR-FET current-voltage characteristics (the dependences of
the source-drain current on the drain voltages as well as on the back gate and
top gate voltages) for different geometric parameters of the device. It is
shown that the shortening of the top gate can result in a substantial
modification of the GNR-FET current-voltage characteristics.Comment: 8 pages, 8 figure