549 research outputs found
Field-induced insulating states in a graphene superlattice
We report on high-field magnetotransport (B up to 35 T) on a gated
superlattice based on single-layer graphene aligned on top of hexagonal boron
nitride. The large-period moir\'e modulation (15 nm) enables us to access the
Hofstadter spectrum in the vicinity of and above one flux quantum per
superlattice unit cell (Phi/Phi_0 = 1 at B = 22 T). We thereby reveal, in
addition to the spin-valley antiferromagnet at nu = 0, two insulating states
developing in positive and negative effective magnetic fields from the main nu
= 1 and nu = -2 quantum Hall states respectively. We investigate the field
dependence of the energy gaps associated with these insulating states, which we
quantify from the temperature-activated peak resistance. Referring to a simple
model of local Landau quantization of third generation Dirac fermions arising
at Phi/Phi_0 = 1, we describe the different microscopic origins of the
insulating states and experimentally determine the energy-momentum dispersion
of the emergent gapped Dirac quasi-particles
Essential L-Amino Acid-Functionalized Graphene Oxide for Liquid Crystalline Phase Formation
The colloidal 2D materials based on graphene and its modifications are of
great interest when it comes to forming LC phases. These LC phases allow
controlling the orientational order of colloidal particles, paving the way for
the efficient processing of modified graphene with anisotropic properties.
Here, we present the peculiarities of AA functionalization of GO, along with
the formation of its LC phase and orientational behavior in an external
magnetic field. We discuss the influence of pH on the GOLC, ultimately showing
its pH-dependent behavior for GO-AA complexes. In addition, we observe
different GO morphology changes due to the presence of AA functional groups,
namely L-cysteine dimerization on the GO platform. The pH dependency of
AA-functionalized LC phase of GO is examined for the first time. We believe
that our studies will open new possibilities for applications in
bionanotechnologies due to self-assembling properties of LCs and magnificent
properties of GO.Comment: 10 pages, 16 figure
Detecting induced pairing at the Al-InAs interface with a quantum microwave circuit
Superconductor-semiconductor hybrid devices are at the heart of several
proposed approaches to quantum information processing, but their basic
properties remain to be understood. We embed a two-dimensional Al-InAs hybrid
system in a resonant microwave circuit, probing the breakdown of
superconductivity due to an applied magnetic field. We find a strong
fingerprint from the two-component nature of the hybrid system, and
quantitatively compare with a theory that includes the contribution of
intraband pairing in the InAs, as well as the emergence of
Bogoliubov-Fermi surfaces due to magnetic field. Separately resolving the Al
and InAs contributions allows us to determine the carrier density and mobility
in the InAs.Comment: 6+17 pages, 5+13 figure
Solution of the Dirac equation with non-minimal coupling to noncentral three-vector potential
We introduce non-minimal coupling to three-vector potential in the 3+1
dimensional Dirac equation. The potential is noncentral (angular-dependent)
such that the Dirac equation separates completely in spherical coordinates. The
relativistic energy spectrum and spinor wavefunctions are obtained for the case
where the radial component of the vector potential is proportional to 1/r. The
non-minimal coupling presented in this work is a generalization of that which
was introduced by Moshinsky and Szczepaniak in the Dirac-Oscillator problem.Comment: 8 page
Phonon-assisted resonant tunneling of electrons in graphene–boron nitride transistors
We observe a series of sharp resonant features in the differential conductance of graphene-hexagonal boron nitride-graphene tunnel transistors over a wide range of bias voltages between 10 and 200 mV. We attribute them to electron tunneling assisted by the emission of phonons of well-defined energy. The bias voltages at which they occur are insensitive to the applied gate voltage and hence independent of the carrier densities in the graphene electrodes, so plasmonic effects can be ruled out. The phonon energies corresponding to the resonances are compared with the lattice dispersion curves of graphene–boron nitride heterostructures and are close to peaks in the single phonon density of states
Tuning the valley and chiral quantum state of Dirac electrons in van der Waals heterostructures
Chirality is a fundamental property of electrons with the relativistic spectrum found in graphene and topological insulators. It plays a crucial role in relativistic phenomena, such as Klein tunneling, but it is difficult to visualize directly. Here we report the direct observation and manipulation of chirality and pseudospin polarization in the tunneling of electrons between two almost perfectly aligned graphene crystals. We use a strong in-plane magnetic field as a tool to resolve the contributions of the chiral electronic states that have a phase difference between the two components of their vector wavefunction. Our experiments not only shed light on chirality, but also demonstrate a technique for preparing graphene’s Dirac electrons in a particular quantum chiral state in a selected valley
European Young Pediatricians Association: Laying the Foundations for Collaboration, Integration, and Networking among Pediatricians of the Future
Measurements of Transverse Energy Flow in Deep-Inelastic Scattering at HERA
Measurements of transverse energy flow are presented for neutral current
deep-inelastic scattering events produced in positron-proton collisions at
HERA. The kinematic range covers squared momentum transfers Q^2 from 3.2 to
2,200 GeV^2, the Bjorken scaling variable x from 8.10^{-5} to 0.11 and the
hadronic mass W from 66 to 233 GeV. The transverse energy flow is measured in
the hadronic centre of mass frame and is studied as a function of Q^2, x, W and
pseudorapidity. A comparison is made with QCD based models. The behaviour of
the mean transverse energy in the central pseudorapidity region and an interval
corresponding to the photon fragmentation region are analysed as a function of
Q^2 and W.Comment: 26 pages, 8 figures, submitted to Eur. Phys.
Searches at HERA for Squarks in R-Parity Violating Supersymmetry
A search for squarks in R-parity violating supersymmetry is performed in e^+p
collisions at HERA at a centre of mass energy of 300 GeV, using H1 data
corresponding to an integrated luminosity of 37 pb^(-1). The direct production
of single squarks of any generation in positron-quark fusion via a Yukawa
coupling lambda' is considered, taking into account R-parity violating and
conserving decays of the squarks. No significant deviation from the Standard
Model expectation is found. The results are interpreted in terms of constraints
within the Minimal Supersymmetric Standard Model (MSSM), the constrained MSSM
and the minimal Supergravity model, and their sensitivity to the model
parameters is studied in detail. For a Yukawa coupling of electromagnetic
strength, squark masses below 260 GeV are excluded at 95% confidence level in a
large part of the parameter space. For a 100 times smaller coupling strength
masses up to 182 GeV are excluded.Comment: 32 pages, 14 figures, 3 table
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