4,443 research outputs found
A non-dispersive Raman D-band activated by well-ordered interlayer interactions in rotationally stacked bi-layer Graphene
Raman measurements on monolayer graphene folded back upon itself as an
ordered but skew-stacked bilayer (i.e. with interlayer rotation) presents new
mechanism for Raman scattering in sp2 carbons that arises in systems that lack
coherent AB interlayer stacking. Although the parent monolayer does not exhibit
a D-band, the interior of the skewed bilayer produces a strong two-peak Raman
feature near 1350 cm-1; one of these peaks is non-dispersive, unlike all
previously observed D-band features in sp2 carbons. Within a double-resonant
model of Raman scattering, these unusual features are consistent with a skewed
bilayer coupling, wherein one layer imposes a weak but well-ordered
perturbation on the other. The discrete Fourier structure of the rotated
interlayer interaction potential explains the unusual non-dispersive peak near
1350 cm-1
Dirac points with giant spin-orbit splitting in the electronic structure of two-dimensional transition-metal carbides
Two-dimensional (2D) materials, especially their most prominent member,
graphene, have greatly influenced many scientific areas. Moreover, they have
become a base for investigating the relativistic properties of condensed matter
within the emerging field of Dirac physics. This has ignited an intense search
for new materials where charge carriers behave as massless or massive Dirac
fermions. Here, we theoretically show the existence of Dirac electrons in a
series of 2D transition-metal carbides, known as MXenes. They possess twelve
conical crossings in the 1st Brillouin zone with giant spin-orbit splitting.
Our findings indicate that the 2D band structure of MXenes is protected against
external perturbations and preserved even in multilayer phases. These results,
together with the broad possibilities to engineer the properties of these
materials phases, make Dirac MXenes a potential candidate for studying and
developing novel Dirac-physics-based technologies.Comment: 4 figures and supplementar
Direct observation and imaging of a spin-wave soliton with like symmetry
The prediction and realization of magnetic excitations driven by electrical
currents via the spin transfer torque effect, enables novel magnetic
nano-devices where spin-waves can be used to process and store information. The
functional control of such devices relies on understanding the properties of
non-linear spin-wave excitations. It has been demonstrated that spin waves can
show both an itinerant character, but also appear as localized solitons. So
far, it was assumed that localized solitons have essentially cylindrical,
like symmetry. Using a newly developed high-sensitivity time-resolved
magnetic x-ray microscopy, we instead observe the emergence of a novel
localized soliton excitation with a nodal line, i.e. with like symmetry.
Micromagnetic simulations identify the physical mechanism that controls the
transition from to like solitons. Our results suggest a potential new
pathway to design artificial atoms with tunable dynamical states using
nanoscale magnetic devices
- …