402 research outputs found
Near-field coupling of gold plasmonic antennas for sub-100 nm magneto-thermal microscopy
The development of spintronic technology with increasingly dense, high-speed,
and complex devices will be accelerated by accessible microscopy techniques
capable of probing magnetic phenomena on picosecond time scales and at deeply
sub-micron length scales. A recently developed time-resolved magneto-thermal
microscope provides a path towards this goal if it is augmented with a
picosecond, nanoscale heat source. We theoretically study adiabatic
nanofocusing and near-field heat induction using conical gold plasmonic
antennas to generate sub-100 nm thermal gradients for time-resolved
magneto-thermal imaging. Finite element calculations of antenna-sample
interactions reveal focused electromagnetic loss profiles that are either
peaked directly under the antenna or are annular, depending on the sample's
conductivity, the antenna's apex radius, and the tip-sample separation. We find
that the thermal gradient is confined to 40 nm to 60 nm full width at half
maximum for realistic ranges of sample conductivity and apex radius. To
mitigate this variation, which is undesirable for microscopy, we investigate
the use of a platinum capping layer on top of the sample as a thermal
transduction layer to produce heat uniformly across different sample materials.
After determining the optimal capping layer thickness, we simulate the
evolution of the thermal gradient in the underlying sample layer, and find that
the temporal width is below 10 ps. These results lay a theoretical foundation
for nanoscale, time-resolved magneto-thermal imaging.Comment: 24 pages including Supporting Information, 6 figures in the main
text, 4 supporting figure
Optical Dipole Structure and Orientation of GaN Defect Single-Photon Emitters
GaN has recently been shown to host bright, photostable, defect single photon
emitters in the 600-700 nm wavelength range that are promising for quantum
applications. The nature and origin of these defect emitters remain elusive. In
this work, we study the optical dipole structures and orientations of these
defect emitters using the defocused imaging technique. In this technique, the
far-field radiation pattern of an emitter in the Fourier plane is imaged to
obtain information about the structure of the optical dipole moment and its
orientation in 3D. Our experimental results, backed by numerical simulations,
show that these defect emitters in GaN exhibit a single dipole moment that is
oriented almost perpendicular to the wurtzite crystal c-axis. Data collected
from many different emitters shows that the angular orientation of the dipole
moment in the plane perpendicular to the c-axis exhibits a distribution that
shows peaks centered at the angles corresponding to the nearest Ga-N bonds and
also at the angles corresponding to the nearest Ga-Ga (or N-N) directions.
Moreover, the in-plane angular distribution shows little difference among
defect emitters with different emission wavelengths in the 600-700 nm range.
Our work sheds light on the nature and origin of these GaN defect emitters.Comment: 15 pages, 4 figure
Nanoscale magnetization and current imaging using scanning-probe magneto-thermal microscopy
Magnetic microscopy that combines nanoscale spatial resolution with
picosecond scale temporal resolution uniquely enables direct observation of the
spatiotemporal magnetic phenomena that are relevant to future high-speed,
high-density magnetic storage and logic technologies. Magnetic microscopes that
combine these metrics has been limited to facility-level instruments. To
address this gap in lab-accessible spatiotemporal imaging, we develop a
time-resolved near-field magnetic microscope based on magneto-thermal
interactions. We demonstrate both magnetization and current density imaging
modalities, each with spatial resolution that far surpasses the optical
diffraction limit. In addition, we study the near-field and time-resolved
characteristics of our signal and find that our instrument possesses a spatial
resolution on the scale of 100 nm and a temporal resolution below 100 ps. Our
results demonstrate an accessible and comparatively low-cost approach to
nanoscale spatiotemporal magnetic microscopy in a table-top form to aid the
science and technology of dynamic magnetic devices with complex spin textures
Excited-state spin-resonance spectroscopy of V defect centers in hexagonal boron nitride
The recently discovered spin-active boron vacancy (V) defect
center in hexagonal boron nitride (hBN) has high contrast optically-detected
magnetic resonance (ODMR) at room-temperature, with a spin-triplet ground-state
that shows promise as a quantum sensor. Here we report temperature-dependent
ODMR spectroscopy to probe spin within the orbital excited-state. Our
experiments determine the excited-state spin Hamiltonian, including a
room-temperature zero-field splitting of 2.1 GHz and a g-factor similar to that
of the ground-state. We confirm that the resonance is associated with spin
rotation in the excited-state using pulsed ODMR measurements, and we observe
Zeeman-mediated level anti-crossings in both the orbital ground- and
excited-state. Our observation of a single set of excited-state spin-triplet
resonance from 10 to 300 K is consistent with an orbital-singlet, which has
consequences for understanding the symmetry of this defect. Additionally, the
excited-state ODMR has strong temperature dependence of both contrast and
transverse anisotropy splitting, enabling promising avenues for quantum
sensing.Comment: 13 pages with 5 figures and a supplemen
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