140 research outputs found
Many-body excitations in tunneling current spectra of a few-electron quantum dot
Inherent asymmetry in the tunneling barriers of few-electron quantum dots
induces intrinsically different tunneling currents for forward and reverse
source-drain biases in the non-linear transport regime. Here we show that in
addition to spin selection rules, overlap matrix elements between many-body
states are crucial for the correct description of tunneling transmission
through quantum dots at large magnetic fields. Signatures of excited
(N-1)-electron states in the transport process through the N-electron system
are clearly identified in the measured transconductances. Our analysis clearly
confirms the validity of single-electron quantum transport theory in quantum
dots.Comment: 5 pages, 2 figure
Localization and entanglement of two interacting electrons in a quantum-dot molecule
The localization of two interacting electrons in a coupled-quantum-dots
semiconductor structure is demonstrated through numerical calculations of the
time evolution of the two-electron wave function including the Coulomb
interaction between the electrons. The transition from the ground state to a
localized state is induced by an external, time-dependent, uniform electric
field. It is found that while an appropriate constant field can localize both
electrons in one of the wells, oscillatory fields can induce roughly equal
probabilities for both electrons to be localized in either well, generating an
interesting type of localized and entangled state. We also show that shifting
the field suddenly to an appropriate constant value can maintain in time both
types of localization.Comment: 4 pages, 4 figure
Experimental Phonon Band Structure of Graphene using C^{13}$ Isotopes
Using very uniform large scale chemical vapor deposition grown graphene
transferred onto silicon, we were able to identify 15 distinct Raman lines
associated with graphene monolayers. This was possible thanks to a combination
of different carbon isotopes and different Raman laser energies and extensive
averaging without increasing the laser power. This allowed us to obtain a
detailed experimental phonon dispersion relation for many points in the
Brillouin zone. We further identified a D+D' peak corresponding to a double
phonon process involving both an inter- and intra-valley phonon.Comment: 5 pages, 4 figures, 1 tabl
Direct Coulomb and Exchange Interaction in Artificial Atoms
We determine the contributions from the direct Coulomb and exchange
interactions to the total interaction in semiconductor artificial atoms. We
tune the relative strengths of the two interactions and measure them as a
function of the number of confined electrons. We find that electrons tend to
have parallel spins when they occupy nearly degenerate single-particle states.
We use a magnetic field to adjust the single-particle state degeneracy, and
find that the spin-configurations in an arbitrary magnetic field are well
explained in terms of two-electron singlet and triplet states.Comment: 4 pages, 5 figure
Tuning the electrically evaluated electron Lande g factor in GaAs quantum dots and quantum wells of different well widths
We evaluate the Lande g factor of electrons in quantum dots (QDs) fabricated
from GaAs quantum well (QW) structures of different well width. We first
determine the Lande electron g factor of the QWs through resistive detection of
electron spin resonance and compare it to the enhanced electron g factor
determined from analysis of the magneto-transport. Next, we form laterally
defined quantum dots using these quantum wells and extract the electron g
factor from analysis of the cotunneling and Kondo effect within the quantum
dots. We conclude that the Lande electron g factor of the quantum dot is
primarily governed by the electron g factor of the quantum well suggesting that
well width is an ideal design parameter for g-factor engineering QDs
Dissociation of vertical semiconductor diatomic artificial molecules
We investigate the dissociation of few-electron circular vertical
semiconductor double quantum dot artificial molecules at 0 T as a function of
interdot distance. Slight mismatch introduced in the fabrication of the
artificial molecules from nominally identical constituent quantum wells induces
localization by offsetting the energy levels in the quantum dots by up to 2
meV, and this plays a crucial role in the appearance of the addition energy
spectra as a function of coupling strength particularly in the weak coupling
limit.Comment: Accepted for publication in Phys. Rev. Let
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