1,068 research outputs found
-factor anisotropy in nanowire-based InAs quantum dots
The determination and control of the electron -factor in semiconductor
quantum dots (QDs) are fundamental prerequisites in modern concepts of
spintronics and spin-based quantum computation. We study the dependence of the
-factor on the orientation of an external magnetic field in quantum dots
(QDs) formed between two metallic contacts on stacking fault free InAs
nanowires. We extract the -factor from the splitting of Kondo resonances and
find that it varies continuously in the range between and 15.Comment: 2 pages, 2 figure
Non-local spectroscopy of Andreev bound states
We experimentally investigate Andreev bound states (ABSs) in a carbon
nanotube quantum dot (QD) connected to a superconducting Nb lead (S). A weakly
coupled normal metal contact acts as a tunnel probe that measures the energy
dispersion of the ABSs. Moreover we study the response of the ABS to non-local
transport processes, namely Cooper pair splitting and elastic co-tunnelling,
that are enabled by a second QD fabricated on the same nanotube on the opposite
side of S. We find an appreciable non-local conductance with a rich structure,
including a sign reversal at the ground state transition from the ABS singlet
to a degenerate magnetic doublet. We describe our device by a simple rate
equation model that captures the key features of our observations and
demonstrates that the sign of the non-local conductance is a measure for the
charge distribution of the ABS, given by the respective Bogoliubov-de Gennes
amplitudes and
Large-scale BN tunnel barriers for graphene spintronics
We have fabricated graphene spin-valve devices utilizing scalable materials
made from chemical vapor deposition (CVD). Both the spin-transporting graphene
and the tunnel barrier material are CVD-grown. The tunnel barrier is realized
by h-BN, used either as a monolayer or bilayer and placed over the graphene.
Spin transport experiments were performed using ferromagnetic contacts
deposited onto the barrier. We find that spin injection is still greatly
suppressed in devices with a monolayer tunneling barrier due to resistance
mismatch. This is, however, not the case for devices with bilayer barriers. For
those devices, a spin relaxation time of 260 ps intrinsic to the CVD graphene
material is deduced. This time scale is comparable to those reported for
exfoliated graphene, suggesting that this CVD approach is promising for
spintronic applications which require scalable materials.Comment: 13 pages, 3 figure
Role of hexagonal boron nitride in protecting ferromagnetic nanostructures from oxidation
Ferromagnetic contacts are widely used to inject spin polarized currents into
non-magnetic materials such as semiconductors or 2-dimensional materials like
graphene. In these systems, oxidation of the ferromagnetic materials poses an
intrinsic limitation on device performance. Here we investigate the role of
ex-situ transferred chemical vapour deposited hexagonal boron nitride (hBN) as
an oxidation barrier for nanostructured cobalt and permalloy electrodes. The
chemical state of the ferromagnets was investigated using X-ray photoemission
electron microscopy owing to its high sensitivity and lateral resolution. We
have compared the oxide thickness formed on ferromagnetic nanostructures
covered by hBN to uncovered reference structures. Our results show that hBN
reduces the oxidation rate of ferromagnetic nanostructures suggesting that it
could be used as an ultra-thin protection layer in future spintronic devices.Comment: 7 pages, 6 figure
Entanglement witnessing and quantum cryptography with non-ideal ferromagnetic detectors
We investigate theoretically the use of non-ideal ferromagnetic contacts as a
mean to detect quantum entanglement of electron spins in transport experiments.
We use a designated entanglement witness and find a minimal spin polarization
of required to demonstrate spin entanglement.
This is significantly less stringent than the ubiquitous tests of Bell's
inequality with . In addition, we discuss the
impact of decoherence and noise on entanglement detection and apply the
presented framework to a simple quantum cryptography protocol. Our results are
directly applicable to a large variety of experiments.Comment: 10 pages, 4 figure
Electrical conductance of molecular junctions by a robust statistical analysis
We propose an objective and robust method to extract the electrical
conductance of single molecules connected to metal electrodes from a set of
measured conductance data. Our method roots in the physics of tunneling and is
tested on octanedithiol using mechanically controllable break junctions. The
single molecule conductance values can be deduced without the need for data
selection.Comment: 4 figure
In-situ strain tuning in hBN-encapsulated graphene electronic devices
Using a simple setup to bend a flexible substrate, we demonstrate
deterministic and reproducible in-situ strain tuning of graphene electronic
devices. Central to this method is the full hBN encapsulation of graphene,
which preserves the exceptional quality of pristine graphene for transport
experiments. In addition, the on-substrate approach allows one to exploit
strain effects in the full range of possible sample geometries and at the same
time guarantees that changes in the gate capacitance remain negligible during
the deformation process. We use Raman spectroscopy to spatially map the strain
magnitude in devices with two different geometries and demonstrate the
possibility to engineer a strain gradient, which is relevant for accessing the
valley degree of freedom with pseudo-magnetic fields. Comparing the transport
characteristics of a suspended device with those of an on-substrate device, we
demonstrate that our new approach does not suffer from the ambiguities
encountered in suspended devices
Snake Trajectories in Ultraclean Graphene p-n Junctions
Snake states are trajectories of charge carriers curving back and forth along
an interface. There are two types of snake states, formed by either inverting
the magnetic field direction or the charge carrier type at an interface.
Whereas the former has been demonstrated in GaAs-AlGaAs heterostructures, the
latter has become conceivable only with the advance of ballistic graphene where
a gapless p-n interface governed by Klein tunneling can be formed. Such snake
states were hidden in previous experiments due to limited sample quality. Here
we report on magneto-conductance oscillations due to snake states in a
ballistic suspended graphene p-n-junction which occur already at a very small
magnetic field of 20mT. The visibility of 30% is enabled by Klein collimation.
Our finding is firmly supported by quantum transport simulations. We
demonstrate the high tunability of the device and operate it in different
magnetic field regimesComment: Accepted for publication in Nature Communication
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