681 research outputs found
Plasma mechanisms of resonant terahertz detection in two-dimensional electron channel with split gates
We analyze the operation of a resonant detector of terahertz (THz) radiation
based on a two-dimensional electron gas (2DEG) channel with split gates. The
side gates are used for the excitation of plasma oscillations by incoming THz
radiation and control of the resonant plasma frequencies. The central gate
provides the potential barrier separating the source and drain portions of the
2DEG channel. Two possible mechanisms of the detection are considered: (1)
modulation of the ac potential drop across the barrier and (2) heating of the
2DEG due to the resonant plasma-assisted absorption of THz radiation followed
by an increase in thermionic dc current through the barrier. Using the device
model we calculate the frequency and temperature dependences of the detector
responsivity associated with both dynamic and heating (bolometric) mechanisms.
It is shown that the dynamic mechanisms dominates at elevated temperatures,
whereas the heating mechanism provides larger contribution at low temperatures,
T=35-40 K.Comment: 7 pages, 4 figure
Phase diagram of a frustrated mixed-spin ladder with diagonal exchange bonds
Using exact numerical diagonalization and the conformal field theory
approach, we study the effect of magnetic frustrations due to diagonal exchange
bonds in a system of two coupled mixed-spin Heisenberg chains. It
is established that relatively moderate frustrations are able to destroy the
ferrimagnetic state and to stabilize the critical spin-liquid phase typical for
half-integer-spin antiferromagnetic Heisenberg chains. Both phases are
separated by a narrow but finite region occupied by a critical
partially-polarized ferromagnetic phase.Comment: 5 PRB pages, 7 eps figures, to appear in Phys. Rev.
Double-Exchange Model on Triangle Chain
We study ground state properties of the double-exchange model on triangle
chain in the classical limit on spins. The ground state is determined
by a competition among the kinetic energy of the electron, the
antiferromagnetic exchange energy between the spins, and frustration
due to a geometric structure of the lattice. The phase diagrams are obtained
numerically for two kinds of the models which differ only in the transfer
integral being real or complex. The properties of the states are understood
from the viewpoint of the spin-induced Peierls instability. The results suggest
the existence of a chiral glass phase which is characterized by a local spin
chirality and a continuous degeneracy.Comment: 6 pages, 4 figure
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