86 research outputs found
Local and nonlocal spin Seebeck effect in lateral Pt--Pt devices at low temperatures
We have studied thermally driven magnon spin transport (spin Seebeck effect,
SSE) in heterostructures of antiferromagnetic - and
Pt at low temperatures. Monitoring the amplitude of the local and nonlocal SSE
signals as a function of temperature, we found that both decrease with
increasing temperature and disappear above 100 K and 20 K, respectively.
Additionally, both SSE signals show a tendency to saturate at low temperatures.
The nonlocal SSE signal decays exponentially for intermediate injector-detector
separation, consistent with magnon spin current transport in the relaxation
regime. We estimate the magnon relaxation length of our
- films to be around 500 nm at 3 K. This short magnon
relaxation length along with the strong temperature dependence of the SSE
signal indicates that temperature-dependent inelastic magnon scattering
processes play an important role in the intermediate range magnon transport.
Our observation is relevant to low-dissipation antiferromagnetic magnon memory
and logic devices involving thermal magnon generation and transport.Comment: Accepted in APL Materials, For Supplementary Material see published
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Autocorrected off-axis holography of two-dimensional materials
The reduced dimensionality in two-dimensional materials leads to a wealth of unusual properties, which are currently explored for both fundamental and applied sciences. In order to study the crystal structure, edge states, the formation of defects and grain boundaries, or the impact of adsorbates, high-resolution microscopy techniques are indispensable. Here we report on the development of an electron holography (EH) transmission electron microscopy (TEM) technique, which facilitates high spatial resolution by an automatic correction of geometric aberrations. Distinguished features of EH beyond conventional TEM imaging are gap-free spatial information signal transfer and higher dose efficiency for certain spatial frequency bands as well as direct access to the projected electrostatic potential of the two-dimensional material. We demonstrate these features with the example of h-BN, for which we measure the electrostatic potential as a function of layer number down to the monolayer limit and obtain evidence for a systematic increase of the potential at the zig-zag edges
On-chip lateral Si:Te PIN photodiodes for room-temperature detection in the telecom optical wavelength bands
Photonic integrated circuits require photodetectors that operate at room
temperature with sensitivity at telecom wavelengths and are suitable for
integration with planar complementary-metal-oxide-semiconductor (CMOS)
technology. Silicon hyperdoped with deep-level impurities is a promising
material for silicon infrared detectors because of its strong room-temperature
photoresponse in the short-wavelength infrared region caused by the creation of
an impurity band within the silicon band gap. In this work, we present the
first experimental demonstration of lateral Te-hyperdoped Si PIN photodetectors
operating at room temperature in the optical telecom bands. We provide a
detailed description of the fabrication process, working principle, and
performance of the photodiodes, including their key figure of merits. Our
results are promising for the integration of active and passive photonic
elements on a single Si chip, leveraging the advantages of planar CMOS
technology.Comment: 18 pages, 5 Figures, Supplementary informatio
Wafer-scale nanofabrication of telecom single-photon emitters in silicon
A highly promising route to scale millions of qubits is to use quantum photonic integrated circuits (PICs), where deterministic photon sources, reconfigurable optical elements, and single-photon detectors are monolithically integrated on the same silicon chip. The isolation of single-photon emitters, such as the G centers and W centers, in the optical telecommunication O-band, has recently been realized in silicon. In all previous cases, however, single-photon emitters were created uncontrollably in random locations, preventing their scalability. Here, we report the controllable fabrication of single G and W centers in silicon wafers using focused ion beams (FIB) with high probability. We also implement a scalable, broad-beam implantation protocol compatible with the complementary-metal-oxide-semiconductor (CMOS) technology to fabricate single telecom emitters at desired positions on the nanoscale. Our findings unlock a clear and easily exploitable pathway for industrial-scale photonic quantum processors with technology nodes below 100 nm
Photoluminescence dynamics in few-layer InSe
We study the optical properties of thin flakes of InSe encapsulated in hBN. More specifically, we investigate the photoluminescence (PL) emission and its dependence on sample thickness and temperature. Through the analysis of the PL lineshape, we discuss the relative weights of the exciton and electron-hole contributions. Thereafter we investigate the PL dynamics. Two contributions are distinguishable at low temperature: direct bandgap electron-hole and defect-assisted recombination. The two recombination processes have lifetime of τ1 ∼ 8 ns and τ2 ∼ 100 ns, respectively. The relative weights of the direct bandgap and defect-assisted contributions show a strong layer dependence due to the direct-to-indirect bandgap crossover. Electron-hole PL lifetime is limited by population transfer to lower-energy states and no dependence on the number of layers was observed. The lifetime of the defect-assisted recombination gets longer for thinner samples. Finally, we show that the PL lifetime decreases at high temperatures as a consequence of more efficient non-radiative recombinations
Mid- and far-infrared localized surface plasmon resonances in chalcogen-hyperdoped silicon
Plasmonic sensing in the infrared region employs the direct interaction of
the vibrational fingerprints of molecules with the plasmonic resonances,
creating surface-enhanced sensing platforms that are superior than the
traditional spectroscopy. However, the standard noble metals used for plasmonic
resonances suffer from high radiative losses as well as fabrication challenges,
such as tuning the spectral resonance positions into mid- to far-infrared
regions, and the compatibility issue with the existing complementary
metal-oxide-semiconductor (CMOS) manufacturing platform. Here, we demonstrate
the occurrence of mid-infrared localized surface plasmon resonances (LSPR) in
thin Si films hyperdoped with the known deep-level impurity tellurium. We show
that the mid-infrared LSPR can be further enhanced and spectrally extended to
the far-infrared range by fabricating two-dimensional arrays of
micrometer-sized antennas in a Te-hyperdoped Si chip. Since Te-hyperdoped Si
can also work as an infrared photodetector, we believe that our results will
unlock the route toward the direct integration of plasmonic sensors with the
one-chip CMOS platform, greatly advancing the possibility of mass manufacturing
of high-performance plasmonic sensing systems.Comment: 20 pages, 5 figure
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