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1. Sensitivity of resonance frequency in the detection of thin layer using nano-slit structures

   https://doi.org/10.1093/imamat/hxaa041  

   Lin, Junshan; Oh, Sang-Hyun; Zhang, Hai (November 2020, IMA Journal of Applied Mathematics)

   null (Ed.)

   Abstract We derive the formulas for the resonance frequencies and their sensitivity when the nano-slit structures are used in the detection of thin layers. For a thin layer with a thickness of $$H$$ deposited over the nanostructure, we show quantitatively that for both single and periodic slit structures with slit aperture size $$\delta $$, the sensitivity of resonance frequency reduces as $$H$$ increases. Specifically, the sensitivity is of order $$O(\delta /H)$$ if $$H>\delta $$ and of order $$O(1+\ln H/\delta )$$ otherwise. The evanescent wave modes are present along the interface between the thin dielectric film and ambient medium above. From the mathematical derivations, it is observed that the sensitivity of the resonance frequency highly depends on the effect of evanescent wave modes on the tiny slit apertures. 

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2. Unidirectional microwave transduction with chirality selected short-wavelength magnon excitations

   https://doi.org/10.1063/5.0156369  

   Li, Yi; Lo, Tzu-Hsiang; Lim, Jinho; Pearson, John E.; Divan, Ralu; Zhang, Wei; Welp, Ulrich; Kwok, Wai-Kwong; Hoffmann, Axel; Novosad, Valentine (July 2023, Applied Physics Letters)

   Nonreciprocal magnon propagation has recently become a highly potential approach of developing chip-embedded microwave isolators for advanced information processing. However, it is challenging to achieve large nonreciprocity in miniaturized magnetic thin-film devices because of the difficulty of distinguishing propagating surface spin waves along the opposite directions when the film thickness is small. In this work, we experimentally realize unidirectional microwave transduction with sub-micrometer-wavelength propagating magnons in a yttrium iron garnet (YIG) thin-film delay line. We achieve a non-decaying isolation of 30 dB with a broad field-tunable bandpass frequency range up to 14 GHz. The large isolation is due to the selection of chiral magnetostatic surface spin waves with the Oersted field generated from the coplanar waveguide antenna. Increasing the geometry ratio between the antenna width and YIG thickness drastically reduces the nonreciprocity and introduces additional magnon transmission bands. Our results pave the way for on-chip microwave isolation and tunable delay line with short-wavelength magnonic excitations. 

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3. Controlling the shape and topology of two-component colloidal membranes

   https://doi.org/10.1073/pnas.2204453119  

   Khanra, Ayantika; Jia, Leroy L.; Mitchell, Noah P.; Balchunas, Andrew; Pelcovits, Robert A.; Powers, Thomas R.; Dogic, Zvonimir; Sharma, Prerna (August 2022, Proceedings of the National Academy of Sciences)

   Changes in the geometry and topology of self-assembled membranes underlie diverse processes across cellular biology and engineering. Similar to lipid bilayers, monolayer colloidal membranes have in-plane fluid-like dynamics and out-of-plane bending elasticity. Their open edges and micrometer-length scale provide a tractable system to study the equilibrium energetics and dynamic pathways of membrane assembly and reconfiguration. Here, we find that doping colloidal membranes with short miscible rods transforms disk-shaped membranes into saddle-shaped surfaces with complex edge structures. The saddle-shaped membranes are well approximated by Enneper’s minimal surfaces. Theoretical modeling demonstrates that their formation is driven by increasing the positive Gaussian modulus, which in turn, is controlled by the fraction of short rods. Further coalescence of saddle-shaped surfaces leads to diverse topologically distinct structures, including shapes similar to catenoids, trinoids, four-noids, and higher-order structures. At long timescales, we observe the formation of a system-spanning, sponge-like phase. The unique features of colloidal membranes reveal the topological transformations that accompany coalescence pathways in real time. We enhance the functionality of these membranes by making their shape responsive to external stimuli. Our results demonstrate a pathway toward control of thin elastic sheets’ shape and topology—a pathway driven by the emergent elasticity induced by compositional heterogeneity. 

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4. Scale statistics of current sheets in relativistic collisionless plasma turbulence

   https://doi.org/10.1017/S002237782500011X  

   Serrano, Roberto F; Nättilä, Joonas; Zhdankin, Vladimir (April 2025, Journal of Plasma Physics)

   We analyse distributions of the spatial scales of coherent intermittent structures – current sheets – obtained from fully kinetic, two-dimensional simulations of relativistic turbulence in a collisionless pair plasma using unsupervised machine-learning data dissection. We find that the distribution functions of sheet length (longest scale of the analysed structure in the direction perpendicular to the dominant guide field) and r_c (radius of a circle fitted to the structures) can be well-approximated by power-law distributions, indicating self-similarity of the structures. The distribution for the sheet width (shortest scale of the structure) peaks at the kinetic scales and decays exponentially at larger values. The data shows little or no correlation between width and length, as expected from theoretical considerations. The typical r_c depends linearly on length, which indicates that the sheets all have a similar curvature relative to their sizes. We find a weak correlation between r_c and width. Our results can be used to inform realistic magnetohydrodynamic subgrid models for plasma turbulence in high-energy astrophysics. 

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5. Rotation–translation coupling of soft objects in lubricated contact

   https://doi.org/10.1039/d2sm00434h  

   Kargar-Estahbanati, Arash; Rallabandi, Bhargav (July 2022, Soft Matter)

   We study the coupling between rotation and translation of a submerged cylinder in lubricated contact with a soft elastic substrate. Using numerical solutions and asymptotic theory, we analyze the elastohydrodynamic problem over the entire range of substrate deformations relative to the thickness of the intervening fluid film. We find a strong coupling between the rotation and translation of the cylinder when the surface deformation of the substrate is comparable to the thickness of the lubricating fluid layer. In the limit of large deformations, we show that the bodies are in near-Hertzian contact and cylinder rolls without slip, reminiscent of dry frictional contact. When the surface deformation is small relative to the separation between the surfaces, the coupling persists but is weaker, and the rotation rate scales with the translation speed to the one-third power. We then show how the external application of a torque modifies these behaviors by generating different combinations of rotational and translational motions, including back-spinning and top-spinning states. We demonstrate that these behaviors are robust regardless of whether the elastic substrate is thick or thin relative to the length scales of the flow. 

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