arXiv subjects

C. F. Destefani

Publications and source records attributed to C. F. Destefani.

8 recordsLinked to original sources

arXiv2005

Transport properties of nano-devices: One-dimensional model study

A 1D model study of charge transport in nano-devices is made by comparing multi-configuration time dependent Hartree-Fock and frozen core calculations. The influence of exchange and Coulomb correlation on the tunneling current is determined. We identify the shape of the tunneling barrier and the resonance structure of the nano-device as the two dominant parameters determining the electron transport. Whereas the barrier shape determines the size of the tunneling current, the resonances determine the structure of the current.

cond-mat.mes-hall↗

arXiv2004

Oscillatory spin relaxation rates in quantum dots

Phonon-induced spin relaxation rates in quantum dots are studied as function of in-plane and perpendicular magnetic fields, temperature and electric field, for different dot sizes. We consider Rashba and Dresselhaus spin-orbit mixing in diferent materials, and show how Zeeman sublevels can relax via piezoelectric and deformation potential coupling to acoustic phonons. We find that strong lateral and vertical confinements may induce minima in the rates at particular values of the magnetic field, where spin relaxation times can reach even seconds. We obtain good agreement with experimental findings in GaAs quantum dots.

cond-mat.mes-hall↗

arXiv2004

Anisotropic electron g-factor in quantum dots with spin-orbit interaction

g-factor tuning of electrons in quantum dots is studied as function of in-plane and perpendicular magnetic fields for different confinements. Rashba and Dresselhaus effects are considered, and comparison is made between wide- and narrow-gap materials. The interplay between magnetic fields and intrinsic spin-orbit coupling is analyzed, with two distinct phases found in the spectrum for GaAs in perpendicular field. The anisotropy of the g-factor is reported, and good agreement with available experimental findings is obtained.

cond-mat.mes-hall↗

arXiv2004

Multichannel field-effect spin barrier selector

We have studied spin carrier dynamics under full spin-orbit coupling. The anisotropy of dispersions for independent circular spinor polarizations is explored as a possible vertical multichannel voltage controlled spin-filter. Small voltage variations are found to select the current polarizations in a resonant tunneling geometry.

cond-mat.mes-hall↗

arXiv2004

Spin-orbit coupling and magnetic spin states in cylindrical quantum dots

We make detailed analysis of each possible spin-orbit coupling of zincblende narrow-gap cylindrical quantum dots built in two-dimensional electron gas. These couplings are related to both bulk (Dresselhaus) and structure (Rashba) inversion asymmetries. We study the competition between electron-electron and spin-orbit interactions on electronic properties of 2-electron quantum dots.

physics.atom-ph↗

arXiv2004

Restricted and unrestricted Hartree-Fock approaches for addition spectrum and Hund's rule of spherical quantum dots in a magnetic field

The Roothaan and Pople-Nesbet approaches for real atoms are adapted to quantum dots in the presence of a magnetic field. Single-particle Gaussian basis sets are constructed, for each dot radius, under the condition of maximum overlap with the exact functions. The chemical potential, the charging energy and the total spin expected values have been calculated, and we have verified the validity of the quantum dot energy shell structure as well as the Hund rule for electronic occupation at zero magnetic field. For finite field, we have observed the violation of Hund's rule and studied the influence of magnetic field on the closed and open energy shell configurations. We have also compared the present results with those obtained with LS-coupling scheme for low electronic occupation numbers. We focus only on ground state properties and consider quantum dots populated up to forty electrons, constructed by GaAs or InSb semiconductors.

physics.atom-ph↗

arXiv2004

The violation of the Hund's rule in semiconductor artificial atoms

The unrestricted Pople-Nesbet approach for real atoms is adapted to quantum dots, the man-made artificial atoms, under applied magnetic field. Gaussian basis sets are used instead of the exact single-particle orbitals in the construction of the appropriated Slater determinants. Both system chemical potential and charging energy are calculated, as also the expected values for total and z-component in spin states. We have verified the validity of the energy shell structure as well as the Hund's rule state population at zero magnetic field. Above given fields, we have observed a violation of the Hund's rule by the suppression of triplets and quartets states at the 1p energy shell, taken as an example. We also compare our present results with those obtained using the LS-coupling scheme for low electronic occupations. We have focused our attention to ground-state properties for GaAs quantum dots populated up to forty electrons.

cond-mat.mes-hall↗

arXiv2003

Spin-orbit coupling and intrinsic spin mixing in quantum dots

Spin-orbit coupling effects are studied in quantum dots in InSb, a narrow-gap material. Competition between different Rashba and Dresselhaus terms is shown to produce wholesale changes in the spectrum. The large (and negative) $g$-factor and the Rashba field produce states where spin is no longer a good quantum number and intrinsic flips occur at moderate magnetic fields. For dots with two electrons, a singlet-triplet mixing occurs in the ground state, with observable signatures in intraband FIR absorption, and possible importance in quantum computation.

cond-mat.mes-hall↗