14,397 research outputs found
Spin Hot Spots in vertically-coupled Few-electron Quantum Dots
The effects of spin-orbit (SO) coupling arising from the confinement
potential in single and two vertically-coupled quantum dots have been
investigated. Our work indicates that a dot containing a single electron shows
the lifting of the degeneracy of dipole-allowed transitions at B=0 due to the
SO coupling which disappears for a dot containing two electrons. For coupled
dots with one electron in each dot, the optical spectra is not affected by the
coupling and is the same as the dot containing one electron. However, for the
case of two coupled dots where one partner dot has two interacting electrons
while the other dot has only one electron, a remarkable effect is observed
where the oscillator strength of two out of four dipole-allowed transition
lines disappears as the distance between the dots is decreased
The Fractional Quantum Hall States of Dirac Electrons in Graphene
We have investigated the fractional quantum Hall states for the Dirac
electrons in a graphene layer in different Landau levels. The relativistic
nature of the energy dispersion relation of the electrons in the graphene
significantly modifies the inter-electron interactions. This results in a
specific dependence of the ground state energy and the energy gaps for
electrons on the Landau level index. For the valley-polarized states, i.e. at
\nu =1/m, m being an odd integer, the energy gaps have the largest values in
the n=1 Landau level. For the valley-unpolarized states, e.g., for the 2/3
state, the energy gaps are suppressed for the n=1 Landau level as compared to
the n=0 level. For both the n=1 and n=0 Landau levels the ground state of the
2/3 system is fully valley-unpolarized.Comment: accepted for publication in Phys. Rev. Let
Hamiltonian Formulation of Quantum Hall Skyrmions with Hopf Term
We study the nonrelativistic nonlinear sigma model with Hopf term in this
paper. This is an important issue beacuse of its relation to the currently
interesting studies in skyrmions in quantum Hall systems. We perform the
Hamiltonian analysis of this system in variables. When the coefficient
of the Hopf term becomes zero we get the Landau-Lifshitz description of the
ferromagnets. The addition of Hopf term dramatically alters the Hamiltonian
analysis. The spin algebra is modified giving a new structure and
interpretation to the system. We point out momentum and angular momentum
generators and new features they bring in to the system.Comment: 16pages, Latex file, typos correcte
Magnetic field induced luminescence spectra in a quantum cascade laser
We report on our study of the luminescence spectra of a quantum cascade laser
in the presence of an external magnetic field tilted from the direction
perpendicular to the electron plane. The effect of the tilted field is to allow
novel optical transitions because of the coupling of intersubband-cyclotron
energies. We find that by tuning the applied field, one can get optical
transitions at different energies that are as sharp as the zero-field
transitions.Comment: 4 pages (LaTex format), 3 figures (postscript
Thermalization of hot electrons via interfacial electron-magnon interaction
Recent work on layered structures of superconductors (S) or normal metals (N)
in contact with ferromagnetic insulators (FI) has shown how the properties of
the previous can be strongly affected by the magnetic proximity effect due to
the static FI magnetization. Here we show that such structures can also exhibit
a new electron thermalization mechanism due to the coupling of electrons with
the dynamic magnetization, i.e., magnons in FI. We here study the heat flow
between the two systems and find that in thin films the heat conductance due to
the interfacial electron-magnon collisions can dominate over the well-known
electron-phonon coupling below a certain characteristic temperature that can be
straightforwardly reached with present-day experiments. We also study the role
of the magnon band gap and the induced spin-splitting field induced in S on the
resulting heat conductance and show that heat balance experiments can reveal
information about such quantities in a way quite different from typical magnon
spectroscopy experiments
Temperature dependence of spin polarizations at higher Landau Levels
We report our results on temperature dependence of spin polarizations at
in the lowest as well as in the next higher Landau level that compare
well with recent experimental results. At , except having a much smaller
magnitude the behavior of spin polarization is not much influenced by higher
Landau levels. In sharp contrast, for filling factor we predict
that unlike the case of the system remains fully spin polarized
even at vanishingly small Zeeman energies.Comment: 4 pages, REVTEX, and 3 .ps files, To be published in Physical Review
Letter
Optical Signatures of Spin-Orbit Interaction Effects in a Parabolic Quantum Dot
We demonstrate here that the dipole-allowed optical absorption spectrum of a
parabolic quantum dot subjected to an external magnetic field reflects the
inter-electron interaction effects when the spin-orbit interaction is also
taken into account. We have investigated the energy spectra and the
dipole-allowed transition energies for up to four interacting electrons
parabolically confined, and have uncovered several novel features in those
spectra that are solely due to the SO interaction.Comment: 4 pages, 3 figure
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