4,489 research outputs found
Kondo and Dicke effect in quantum-dots side coupled to a quantum wire
Electron tunneling through quantum-dots side coupled to a quantum wire, in
equilibrium and nonequilibrium Kondo regime, is studied. The mean-field
finite- slave-boson formalism is used to obtain the solution of the problem.
We have found that the transmission spectrum shows a structure with two
anti-resonances localized at the renormalized energies of the quantum dots. The
DOS of the system shows that when the Kondo correlations are dominant there are
two Kondo regimes with its own Kondo temperature. The above behavior of the DOS
can be explained by quantum interference in the transmission through the two
different resonance states of the quantum dots coupled to common leads. This
result is analogous to the Dicke effect in optics. We investigate the many body
Kondo states as a function of the parameters of the system.Comment: 5 figures. To appear in Phys. Rev.
Self-compensation in phosphorus-doped CdTe
We investigate the self-compensation mechanism in phosphorus-doped CdTe. The
formation energies, charge transition levels, and defects states of several
P-related point defects susceptible to cause self-compensation are addressed by
first-principles calculations. Moreover, we assess the in uence of the
spin-orbit coupling and supercell-size effects on the stability of AX centers
donors, which are believed to be responsible for most of the self-compensation.
We report an improved result for the lowest-energy configuration of the P
interstitial (P) and find that the self-compensation mechanism is
not due to the formation of AX centers. Under Te-rich growth conditions,
(P) exhibits a formation energy lower than the substitutional
acceptor (P) when the Fermi level is near the valence band, acting
as compensating donor. While, for Cd-rich growth conditions, our results
suggest that p-type doping is limited by the formation of
(P-V) complexes.Comment: 5 page
Dynamic instability in resonant tunneling
We show that an instability may be present in resonant tunneling through a
quantum well in one, two and three dimensions, when the resonance lies near the
emitter Fermi level. A simple semiclassical model which simulates the resonance
and the projected density of states by a nonlinear conductor, the Coulomb
barrier by a capacitance, and the time evolution by an iterated map, is used.
The model reproduces the observed hysteresis in such devices, and exhibits a
series of bifurcations leading to fast chaotic current fluctuations.Comment: 7 pages, 2 figure
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