15 research outputs found
Quantum transport through MoS constrictions defined by photodoping
We present a device scheme to explore mesoscopic transport through molybdenum
disulfide (MoS) constrictions using photodoping. The devices are based on
van-der-Waals heterostructures where few-layer MoS flakes are partially
encapsulated by hexagonal boron nitride (hBN) and covered by a few-layer
graphene flake to fabricate electrical contacts. Since the as-fabricated
devices are insulating at low temperatures, we use photo-induced remote doping
in the hBN substrate to create free charge carriers in the MoS layer. On
top of the device, we place additional metal structures, which define the shape
of the constriction and act as shadow masks during photodoping of the
underlying MoS/hBN heterostructure. Low temperature two- and four-terminal
transport measurements show evidence of quantum confinement effects.Comment: 9 pages, 6 figure
Transport through a strongly coupled graphene quantum dot in perpendicular magnetic field
We present transport measurements on a strongly coupled graphene quantum dot
in a perpendicular magnetic field. The device consists of an etched
single-layer graphene flake with two narrow constrictions separating a 140 nm
diameter island from source and drain graphene contacts. Lateral graphene gates
are used to electrostatically tune the device. Measurements of Coulomb
resonances, including constriction resonances and Coulomb diamonds prove the
functionality of the graphene quantum dot with a charging energy of around 4.5
meV. We show the evolution of Coulomb resonances as a function of perpendicular
magnetic field, which provides indications of the formation of the graphene
specific 0th Landau level. Finally, we demonstrate that the complex pattern
superimposing the quantum dot energy spectra is due to the formation of
additional localized states with increasing magnetic field.Comment: 6 pages, 4 figure
Single device offset-free magnetic field sensing principle with tunable sensitivity and linear range based on spin-orbit-torques
We propose a novel device concept using spin-orbit-torques to realize a
magnetic field sensor, where we eliminate the sensor offset using a
differential measurement concept. We derive a simple analytical formulation for
the sensor signal and demonstrate its validity with numerical investigations
using macrospin simulations. The sensitivity and the measurable linear sensing
range in the proposed concept can be tuned by either varying the effective
magnetic anisotropy or by varying the magnitude of the injected currents. We
show that undesired perturbation fields normal to the sensitive direction
preserve the zero-offset property and only slightly modulate the sensitivity of
the proposed sensor. Higher-harmonics voltage analysis on a Hall cross
experimentally confirms the linearity and tunability via current strength.
Additionally, the sensor exhibits a non-vanishing offset in the experiment
which we attribute to the anomalous Nernst effect.Comment: 12 Pages, 7 Figure
00 [Material gráfico]
Copia digital. Madrid : Ministerio de Educación, Cultura y Deporte, 201
The relevance of electrostatics for scanning-gate microscopy
Scanning-probe techniques have been developed to extract local information from a given physical system. In particular, conductance maps obtained by means of scanning-gate microscopy (SGM), where a conducting tip of an atomic-force microscope is used as a local and movable gate, seem to present an intuitive picture of the underlying physical processes. Here, we argue that the interpretation of such images is complex and not very intuitive under certain circumstances: scanning a graphene quantum dot (QD) in the Coulomb-blockaded regime, we observe an apparent shift of features in scanning-gate images as a function of gate voltages, which cannot be a real shift of the physical system. Furthermore, we demonstrate the appearance of more than one set of Coulomb rings arising from the graphene QD. We attribute these effects to screening between the metallic tip and the gates. Our results are relevant for SGM on any kind of nanostructure, but are of particular importance for nanostructures that are not covered with a dielectric, e.g. graphene or carbon nanotube structures.ISSN:1367-263