14 research outputs found
Excitonic condensation in quasi-two-dimensional systems
We present a low energy model for the Bose-Einstein condensation in a
quasi-two-dimensional excitonic gas. Using the flow equations of the
Renormalization group and a model with the dynamical critical exponent
we calculate the temperature dependence of the critical density,
coherence length, magnetic susceptibility, and specific heat. The model can be
relevant for the macroscopic coherence observed in GaAs/AlGaAs coupled quantum
wells.Comment: 4 Revtex page
Ginzburg-Landau Expansion in Non-Fermi Liquid Superconductors: Effect of the Mass Renormalization Factor
We reconsider the Ginzburg-Landau expansion for the case of a non-Fermi
liquid superconductor. We obtain analytical results for the Ginzburg-Landau
functional in the critical region around the superconducting phase transition,
T <= T_c, in two special limits of the model, i.e., the spin-charge separation
case and the anomalous Fermi liquid case. For both cases, in the presence of a
mass renormalization factor, we derived the form and the specific dependence of
the coherence length, penetration depth, specific heat jump at the critical
point, and the magnetic upper critical field. For both limits the obtained
results reduce to the usual BCS results for a two dimensional s-wave
superconductor. We compare our results with recent and relevant theoretical
work. The results for a d--wave symmetry order parameter do not change
qualitatively the results presented in this paper. Only numerical factors
appear additionally in our expressions.Comment: accepted for publication in Physical Review
Electronic Green's functions in a T-shaped multi-quantum dot system
We developed a set of equations to calculate the electronic Green's functions
in a T-shaped multi-quantum dot system using the equation of motion method. We
model the system using a generalized Anderson Hamiltonian which accounts for
{\em finite} intradot on-site Coulomb interaction in all component dots as well
as for the interdot electron tunneling between adjacent quantum dots. Our
results are obtained within and beyond the Hartree-Fock approximation and
provide a path to evaluate all the electronic correlations in the multi-quantum
dot system in the Coulomb blockade regime. Both approximations provide
information on the physical effects related to the finite intradot on-site
Coulomb interaction. As a particular example for our generalized results, we
considered the simplest T-shaped system consisting of two dots and proved that
our approximation introduces important corrections in the detector and side
dots Green's functions, and implicitly in the evaluation of the system's
transport properties. The multi-quantum dot T-shaped setup may be of interest
for the practical realization of qubit states in quantum dots systems.Comment: 13 pages, 2 figure
Evidence of quantum interference in transport properties of a triple quantum dot T-shape system
We consider the transport and the noise characteristic in the case of a triple quantum dots T-shape system where two of the dots form a two-level system and the other works in a detector-like setup. Our theoretical results are obtained using the equation of motion method for the case of zero and finite on-site Coulomb interaction in the detector dot. We present analytic results for the electronic Green's functions in the system's component quantum dots, and we used numerical calculations to evaluate the system's transport properties. The transport trough the T-shaped system can be controlled by varying the coupling between the two-level system dots or the coupling between the detector dot and the exterior electrodes. The system's conductance presents Fano dips for both strong (fast detector) and weak coupling (slow detector) between the detector dot and the external electrodes. Due to stronger electronic correlations the noise characteristics in the case of a slow detector are much higher. This setup may be of interest for the practical realization of qubit states in quantum dots systems
Manipulating Quantum Coherence in Solid State Systems
The NATO Advanced Study Institute "Manipulating Quantum Coherence in Solid State Systems", in Cluj-Napoca, Romania, August 29-September 9, 2005, presented a fundamental introduction to solid-state approaches to achieving quantum computation. This proceedings volume describes the properties of quantum coherence in semiconductor spin-based systems and the behavior of quantum coherence in superconducting systems. Semiconductor spin-based approaches to quantum computation have made tremendous advances in the past several years. Coherent populations of spins can be oriented, manipulated and detected experimentally. Rapid progress has been made towards performing the same tasks on individual spins (nuclear, ionic, or electronic) with all-electrical means. Superconducting approaches to quantum computation have demonstrated single qubits based on charge eigenstates as well as flux eigenstates. These topics have been presented in a pedagogical fashion by leading researchers in the fields of semiconductor-spin-based quantum coherence and of superconducting quantum coherence
Evidence for a metallic–like state in the T=0 K phase diagram of a high temperature superconductor
We examine the effects of a phenomenological pseudogap on the T=0 K phase diagram of a high temperature superconductor within a self-consistent model which exhibits a d-wave pairing symmetry. At the mean-field level the presence of a pseudogap in the normal phase of the high temperature superconductor is proved to be essential for the existence of a metallic–like state in the density versus interaction phase diagram. In the small density limit, at high attractive interaction, bosonic–like degrees of freedom are likely to emerge. Our result should be relevant for underdoped high temperature superconductors, where there is a strong evidence for the presence of a pseudogap in the excitation spectrum of the normal state quasiparticles. Copyright EDP Sciences/Società Italiana di Fisica/Springer-Verlag 2005