3 research outputs found
Near Field of Strongly Coupled Plasmons: Uncovering Dark Modes
Strongly coupled plasmons in a system of individual gold
nanoparticles
placed at subnanometer distance to a gold film (nanoparticle-on-plane,
NPOP) are investigated using two complementary single particle spectroscopy
techniques. Optical scattering spectroscopy exclusively detects plasmon
modes that couple to the far field via their dipole moment (bright
modes). By using photoemission electron microscopy (PEEM), we detect
in the identical NPOPs near-field modes that do not couple to the
scattered far field (dark modes) and are characterized by a strongly
enhanced nonlinear electron emission process. To our knowledge, this
is the first time that both far- and near-field spectroscopy are carried
out for identical individual nanostructures interacting via a subnanometer
gap. Strongly resonant electron emission occurs at excitation wavelengths
far off-resonant in the scattering spectra
Momentum Distribution of Electrons Emitted from Resonantly Excited Individual Gold Nanorods
Electron emission
by femtosecond laser pulses from individual Au
nanorods is studied with a time-of-flight momentum resolving photoemission
electron microscope (ToF k-PEEM). The Au nanorods adhere to a transparent
indium–tin oxide substrate, allowing for illumination from
the rear side at normal incidence. Localized plasmon polaritons are
resonantly excited at 800 nm with 100 fs long pulses. The momentum
distribution of emitted electrons reveals two distinct emission mechanisms:
a coherent multiphoton photoemission process from the optically heated
electron gas leads to an isotropic emission distribution. In contrast,
an additional emission process resulting from the optical field enhancement
at both ends of the nanorod leads to a strongly directional emission
parallel to the nanorod’s long axis. The relative intensity
of both contributions can be controlled by the peak intensity of the
incident light
Optically Triggered Néel Vector Manipulation of a Metallic Antiferromagnet Mn<sub>2</sub>Au under Strain
The absence of stray fields, their insensitivity to external
magnetic
fields, and ultrafast dynamics make antiferromagnets promising candidates
for active elements in spintronic devices. Here, we demonstrate manipulation
of the Néel vector in the metallic collinear antiferromagnet
Mn2Au by combining strain and femtosecond laser excitation.
Applying tensile strain along either of the two in-plane easy axes
and locally exciting the sample by a train of femtosecond pulses,
we align the Néel vector along the direction controlled by
the applied strain. The dependence on the laser fluence and strain
suggests the alignment is a result of optically triggered depinning
of 90° domain walls and their motion in the direction of the
free energy gradient, governed by the magneto-elastic coupling. The
resulting, switchable state is stable at room temperature and insensitive
to magnetic fields. Such an approach may provide ways to realize robust
high-density memory device with switching time scales in the picosecond
range