We demonstrate strong magnon-photon coupling of a thin-film permalloy device fabricated on a coplanar superconducting resonator. A coupling strength of 0.152 GHz and a cooperativity of 68 are found for a 30-nm-thick permalloy stripe. The coupling strength is tunable by rotating the biasing magnetic field or changing the volume of permalloy. We also observe an enhancement of magnonphoton coupling in the nonlinear regime of the superconducting resonator, which is mediated by the nucleation of dynamic flux vortices. Our results demonstrate a critical step towards future integrated hybrid systems for quantum magnonics and on-chip coherent information transfer.
The spin diffusion length of Pt at room temperature and at 8 K is experimentally determined via spin pumping and spin Hall effect in permalloy/Pt bilayers. Voltages generated during excitation of ferromagnetic resonance from the inverse spin Hall effect and anisotropic magnetoresistance effect were investigated with a broadband approach. Varying the Pt layer thickness gives rise to an evolution of the voltage line shape due to the superposition of the above two effects. By studying the ratio of the two voltage components with the Pt layer thickness, the spin diffusion length of Pt can be directly extracted. We obtain a spin diffusion length of ∼1.2 nm at room temperature and ∼1.6 nm at 8 K.
The need for stimuli-responsive components in microfluidic systems has led to the development of hydrogel-based patterned microstructures. The most commonly practiced means for fabricating micropatterned hydrogels is based on in situ photopolymerization using 365 nm UV light in a liquid medium. This approach has been found to be very successful for patterning hydrogel-based features with tens or hundreds of microns resolution, but its main drawback lies in having to contain the liquid prepolymer mixture within the device for irradiation. We instead propose an alternate approach that uses direct-write electron-beam radiation to cross-link a dry, spin-coated thin film of linear polymer. After exposure, the linear polymer is dissolved in water leaving behind the cross-linked regions. When immersed in water, the cross-linked regions assume the properties of hydrogel and undergo naturally thermoreversible swelling and shrinking. This direct-writing approach can be used to fabricate hydrogel-based nanostructures down to 100 nm linewidth and also is amenable to easy integration into nano and bio devices. We focus on patterning a well-known thermoreversible hydrogel, poly ͑N-isopropylacrylamide͒, and use it to discuss various aspects of process methodology, fabrication, characterization, and stimuli-response properties of nanosized hydrogels in detail.
Abstract-Microfabricated folded waveguide traveling-wave tubes (TWTs) are potential compact sources of wide-band, high-power terahertz radiation. We present feasibility studies of an oscillator concept using an amplifier with delayed feedback. Simulations of a 560-GHz oscillator and experimental evaluation of the concept at 50 GHz are presented. Additionally, results from various fabrication methods that are under investigation, such as X-ray lithography, electroforming, and molding (LIGA), UV LIGA, and deep reactive ion etching are presented. Observations and measurements are reported on the generation of stable single-frequency oscillation states. On varying the feedback level, the oscillation changes from a stable single-frequency state at the threshold to multifrequency spectra in the overdriven state. Simulation and experimental results on amplifier characterization and dynamics of the regenerative TWT oscillator include spectral evolution and phase stability of the generated frequencies. The results of the experiment are in good agreement with the simulations.Index Terms-Delayed feedback oscillator, folded waveguide (FWG) traveling-wave tube (TWT), frequency spectrum, high power, microfabrication, phase, terahertz radiation, wide-band.
It is widely believed that the reflection minimum in a Kretschmann-Raether experiment results from direct coupling into surface plasmon polariton modes. Our experimental results provide a surprising discrepancy between the leakage radiation patterns of surface plasmon polaritons (SPPs) launched on a layered gold/germanium film compared to the K-R minimum, clearly challenging this belief. We provide definitive evidence that the reflectance dip in K-R experiments does not correlate with excitation of an SPP mode, but rather corresponds to a particular type of perfectly absorbing (PA) mode. Results from rigorous electrodynamics simulations show that the PA mode can only exist under external driving, whereas the SPP can exist in regions free from direct interaction with the driving field. These simulations show that it is possible to indirectly excite propagating SPPs guided by the reflectance minimum in a K-R experiment, but demonstrate the efficiency can be lower by more than a factor of 3. We find that optimal coupling into the SPP can be guided by the square magnitude of the Fresnel transmission amplitude.
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