8 research outputs found
Dynamic Visualization of Nanoscale Vortex Orbits
Due to the atomic-scale resolution, scanning tunneling microscopy is an ideal technique to observe the smallest objects. Nevertheless, it suffers from very long capturing times in order to investigate dynamic processes at the nanoscale. We address this issue, for vortex matter in NbSe<sub>2</sub>, by driving the vortices using an ac magnetic field and probing the induced periodic tunnel current modulations. Our results reveal different dynamical modes of the driven vortex lattices. In addition, by recording and synchronizing the time evolution of the tunneling current at each pixel, we visualize the overall dynamics of the vortex lattice with submillisecond time resolution and subnanometer spatial resolution
Mapping Magnetic Near-Field Distributions of Plasmonic Nanoantennas
We present direct experimental mapping of the lateral magnetic near-field distribution in plasmonic nanoantennas using aperture scanning near-field optical microscopy (SNOM). By means of full-field simulations it is demonstrated how the coupling of the hollow-pyramid aperture probe to the nanoantenna induces an effective magnetic dipole which efficiently excites surface plasmon resonances only at lateral magnetic field maxima. This excitation in turn affects the detected light intensity enabling the visualization of the lateral magnetic near-field distribution of multiple odd and even order plasmon modes with subwavelength spatial resolution
Nonlinear Optical Properties of Ag Nanoclusters and Nanoparticles Dispersed in a Glass Host
The nonlinear absorption of Ag atomic
clusters and nanoparticles
dispersed in a transparent oxyfluoride glass host has been studied.
The as-prepared glass, containing 0.15 atom % Ag, shows an absorption
band in the UV/violet attributed to the presence of amorphous Ag atomic
nanoclusters with an average size of 1.2 nm. Upon heat treatment the
Ag nanoclusters coalesce into larger nanoparticles that show a surface
plasmon absorption band in the visible. Open aperture <i>z</i>-scan experiments using 480 nm nanosecond laser pulses demonstrated
nonsaturated and saturated nonlinear absorption with large nonlinear
absorption indices for the Ag nanoclusters and nanoparticles, respectively.
These properties are promising, e.g., for applications in optical
limiting and object’s contrast enhancement
Unidirectional Side Scattering of Light by a Single-Element Nanoantenna
Unidirectional side scattering of
light by a single-element plasmonic
nanoantenna is demonstrated using full-field simulations and back
focal plane measurements. We show that the phase and amplitude matching
that occurs at the Fano interference between two localized surface
plasmon modes in a V-shaped nanoparticle lies at the origin of this
effect. A detailed analysis of the V-antenna modeled as a system of
two coherent point-dipole sources elucidates the mechanisms that give
rise to a tunable experimental directivity as large as 15 dB. The
understanding of Fano-based directional scattering opens a way to
develop new directional optical antennas for subwavelength color routing
and self-referenced directional sensing. In addition, the directionality
of these nanoantennas can increase the detection efficiency of fluorescence
and surface enhanced Raman scattering
Electrically Driven Unidirectional Optical Nanoantennas
Directional
antennas revolutionized modern day telecommunication
by enabling precise beaming of radio and microwave signals with minimal
loss of energy. Similarly, directional optical nanoantennas are expected
to pave the way toward on-chip wireless communication and information
processing. Currently, on-chip integration of such antennas is hampered
by their multielement design or the requirement of complicated excitation
schemes. Here, we experimentally demonstrate electrical driving of
in-plane tunneling nanoantennas to achieve broadband unidirectional
emission of light. Far-field interference, as a result of the spectral
overlap between the dipolar emission of the tunnel junction and the
fundamental quadrupole-like resonance of the nanoantenna, gives rise
to a directional radiation pattern. By tuning this overlap using the
applied voltage, we record directivities as high as 5 dB. In addition
to electrical tunability, we also demonstrate passive tunability of
the directivity using the antenna geometry. These fully configurable
electrically driven nanoantennas provide a simple way to direct optical
energy on-chip using an extremely small device footprint
Near-Field Mapping of Optical Fabry–Perot Modes in All-Dielectric Nanoantennas
Subwavelength
optical resonators and scatterers are dramatically
expanding the toolset of the optical sciences and photonics engineering.
By offering the opportunity to control and shape light waves in nanoscale
volumes, recent developments using high-refractive-index dielectric
scatterers gave rise to efficient flat-optical components such as
lenses, polarizers, phase plates, color routers, and nonlinear elements
with a subwavelength thickness. In this work, we take a deeper look
into the unique interaction of light with rod-shaped amorphous silicon
scatterers by tapping into their resonant modes with a localized subwavelength
light sourcean aperture scanning near-field probe. Our experimental
configuration essentially constitutes a dielectric antenna that is
locally driven by the aperture probe. We show how leaky transverse
electric and magnetic modes can selectively be excited and form specific
near-field distribution depending on wavelength and antenna dimensions.
The probe’s transmittance is furthermore enhanced upon coupling
to the Fabry–Perot cavity modes, revealing all-dielectric nanorods
as efficient transmitter antennas for the radiation of subwavelength
emitters, in addition to constituting an elementary building block
for all-dielectric metasurfaces and flat optics
Bosonic Confinement and Coherence in Disordered Nanodiamond Arrays
In
the presence of disorder, superconductivity exhibits short-range
characteristics linked to localized Cooper pairs which are responsible
for anomalous phase transitions and the emergence of quantum states
such as the bosonic insulating state. Complementary to well-studied
homogeneously disordered superconductors, superconductor-normal hybrid
arrays provide tunable realizations of the degree of granular disorder
for studying anomalous quantum phase transitions. Here, we investigate
the superconductor–bosonic dirty metal transition in disordered
nanodiamond arrays as a function of the dispersion of intergrain spacing,
which ranges from angstroms to micrometers. By monitoring the evolved
superconducting gaps and diminished coherence peaks in the single-quasiparticle
density of states, we link the destruction of the superconducting
state and the emergence of bosonic dirty metallic state to breaking
of the global phase coherence and persistence of the localized Cooper
pairs. The observed resistive bosonic phase transitions are well modeled
using a series–parallel circuit in the framework of bosonic
confinement and coherence
Superconducting Ferromagnetic Nanodiamond
Superconductivity and ferromagnetism
are two mutually antagonistic
states in condensed matter. Research on the interplay between these
two competing orderings sheds light not only on the cause of various
quantum phenomena in strongly correlated systems but also on the general
mechanism of superconductivity. Here we report on the observation
of the electronic entanglement between superconducting and ferromagnetic
states in hydrogenated boron-doped nanodiamond films, which have a
superconducting transition temperature <i>T</i><sub>c</sub> ∼ 3 K and a Curie temperature <i>T</i><sub>Curie</sub> > 400 K. In spite of the high <i>T</i><sub>Curie</sub>, our nanodiamond films demonstrate a decrease in the temperature
dependence of magnetization below 100 K, in correspondence to an increase
in the temperature dependence of resistivity. These anomalous magnetic
and electrical transport properties reveal the presence of an intriguing
precursor phase, in which spin fluctuations intervene as a result
of the interplay between the two antagonistic states. Furthermore,
the observations of high-temperature ferromagnetism, giant positive
magnetoresistance, and anomalous Hall effect bring attention to the
potential applications of our superconducting ferromagnetic nanodiamond
films in magnetoelectronics, spintronics, and magnetic field sensing