70 research outputs found
Suppression of spin relaxation in an InAs nanowire double quantum dot
We investigate the triplet-singlet relaxation in a double quantum dot defined
by top-gates in an InAs nanowire. In the Pauli spin blockade regime, the
leakage current can be mainly attributed to spin relaxation. While at weak and
strong inter-dot coupling relaxation is dominated by two individual mechanisms,
the relaxation is strongly reduced at intermediate coupling and finite magnetic
field. In addition we observe a charateristic bistability of the spin-non
conserving current as a function of magnetic field. We propose a model where
these features are explained by the polarization of nuclear spins enabled by
the interplay between hyperfine and spin-orbit mediated relaxation.Comment: 5 pages, 4 figure
Measuring current by counting electrons in a nanowire quantum dot
We measure current by counting single electrons tunneling through an InAs
nanowire quantum dot. The charge detector is realized by fabricating a quantum
point contact in close vicinity to the nanowire. The results based on electron
counting compare well to a direct measurements of the quantum dot current, when
taking the finite bandwidth of the detector into account. The ability to detect
single electrons also opens up possibilities for manipulating and detecting
individual spins in nanowire quantum dots
Detecting THz current fluctuations in a quantum point contact using a nanowire quantum dot
We use a nanowire quantum dot to probe high-frequency current fluctuations in
a nearby quantum point contact. The fluctuations drive charge transitions in
the quantum dot, which are measured in real-time with single-electron detection
techniques. The quantum point contact (GaAs) and the quantum dot (InAs) are
fabricated in different material systems, which indicates that the interactions
are mediated by photons rather than phonons. The large energy scales of the
nanowire quantum dot allow radiation detection in the long-wavelength infrared
regime
Self-aligned charge read-out for InAs nanowire quantum dots
A highly sensitive charge detector is realized for a quantum dot in an InAs
nanowire. We have developed a self-aligned etching process to fabricate in a
single step a quantum point contact in a two-dimensional electron gas and a
quantum dot in an InAs nanowire. The quantum dot is strongly coupled to the
underlying point contact which is used as a charge detector. The addition of
one electron to the quantum dot leads to a change of the conductance of the
charge detector by typically 20%. The charge sensitivity of the detector is
used to measure Coulomb diamonds as well as charging events outside the dot.
Charge stability diagrams measured by transport through the quantum dot and
charge detection merge perfectly.Comment: 11 pages, 3 figure
Two-dimensional imaging of the spin-orbit effective magnetic field
We report on spatially resolved measurements of the spin-orbit effective
magnetic field in a GaAs/InGaAs quantum-well. Biased gate electrodes lead to an
electric-field distribution in which the quantum-well electrons move according
to the local orientation and magnitude of the electric field. This motion
induces Rashba and Dresselhaus effective magnetic fields. The projection of the
sum of these fields onto an external magnetic field is monitored locally by
measuring the electron spin-precession frequency using time-resolved Faraday
rotation. A comparison with simulations shows good agreement with the
experimental data.Comment: 6 pages, 4 figure
Dynamics of coupled spins in quantum dots with strong spin-orbit interaction
We investigated the time dependence of two-electron spin states in a double
quantum dot fabricated in an InAs nanowire. In this system, spin-orbit
interaction has substantial influence on the spin states of confined electrons.
Pumping single electrons through a Pauli spin-blockade configuration allowed to
probe the dynamics of the two coupled spins via their influence on the pumped
current. We observed spin-relaxation with a magnetic field dependence different
from GaAs dots, which can be explained by spin-orbit interaction. Oscillations
were detected for times shorter than the relaxation time, which we attribute to
coherent evolution of the spin states.Comment: 5 pages, 4 figure
Optimized stray-field-induced enhancement of the electron spin precession by buried Fe gates
The magnetic stray field from Fe gates is used to modify the spin precession
frequency of InGaAs/GaAs quantum-well electrons in an external magnetic field.
By using an etching process to position the gates directly in the plane of the
quantum well, the stray-field influence on the spin precession increases
significantly compared with results from previous studies with top-gated
structures. In line with numerical simulations, the stray-field-induced
precession frequency increases as the gap between the ferromagnetic gates is
reduced. The inhomogeneous stray field leads to additional spin dephasing.Comment: 4 pages, 2 figure
- …