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1. Eigenmodes of 1-kink skyrmions in cylindrical magnetic discs

   https://doi.org/10.1016/j.jmmm.2024.171761  

   Staggers, Trae L.; Pollard, Shawn D. (February 2024, Journal of Magnetism and Magnetic Materials)

   The stability and resonance spectra associated with a domain wall skyrmion embedded within a Néel skyrmion, forming a 1-kink skyrmion, has been studied using micromagnetic simulations. We show that the 1-kink skyrmion is stable over a wide range of fields at moderate strengths of the Dzyaloshinskii-Moriya interaction. By exciting these structures with a broadband magnetic field excitation, we find complex resonance behavior deviating from that of a pure Néel skyrmion. For out-of-plane excitations, the 1-kink skyrmion demonstrates an additional mode relative to that of the Néel skyrmion at reduced amplitude. These consist of low frequency and high frequency modes associated with both a breathing mode and an oscillation of the embedded domain wall skyrmion. Following an in-plane excitation, both Néel and 1-kink skyrmions exhibit a counterclockwise rotational mode with similar frequencies, as well as a higher frequency mode associated with the interaction of the structure with the ferromagnetic background state. These results may help pave the way for exploration of more complex spin structures for magnetic-based microwave devices. 

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2. Omnimodal topological polarization of bilayer networks: Analysis in the Maxwell limit and experiments on a 3D-printed prototype

   https://doi.org/10.1073/pnas.2208051119  

   Charara, Mohammad; McInerney, James; Sun, Kai; Mao, Xiaoming; Gonella, Stefano (October 2022, Proceedings of the National Academy of Sciences)

   Periodic networks on the verge of mechanical instability, called Maxwell lattices, are known to exhibit zero-frequency modes localized to their boundaries. Topologically polarized Maxwell lattices, in particular, focus these zero modes to one of their boundaries in a manner that is protected against disorder by the reciprocal-space topology of the lattice’s band structure. Here, we introduce a class of mechanical bilayers as a model system for designing topologically protected edge modes that couple in-plane dilational and shearing modes to out-of-plane flexural modes, a paradigm that we refer to as “omnimodal polarization.” While these structures exhibit a high-dimensional design space that makes it difficult to predict the topological polarization of generic geometries, we are able to identify a family of mirror-symmetric bilayers that inherit the in-plane modal localization of their constitutive monolayers, whose topological polarization can be determined analytically. Importantly, the coupling between the layers results in the emergence of omnimodal polarization, whereby in-plane and out-of-plane edge modes localize on the same edge. We demonstrate these theoretical results by fabricating a mirror-symmetric, topologically polarized kagome bilayer consisting of a network of elastic beams via additive manufacturing and confirm this finite-frequency polarization via finite element analysis and laser-vibrometry experiments. 

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3. Tilt Corrections for Normal Mode Observations on Ocean Bottom Seismic Data, an example from the PI-LAB experiment

   https://doi.org/10.26443/seismica.v1i1.196  

   Harmon, Nicholas; Laske, Gabi; Crawford, Wayne; Rychert, Catherine (October 2022, Seismica)

   Earth's normal modes are fundamental observations used in global seismic tomography to understand Earth structure. Land seismic station coverage is sufficient to constrain the broadest scale Earth structures. However, 70% of Earth's surface is covered by the oceans, hampering our ability to observe variations in local mode frequencies that contribute to imaging small-scale structures. Broadband ocean bottom seismometers can record spheroidal modes to fill in gaps in global data coverage. Ocean bottom recordings are contaminated by signals from complex interactions between ocean and solid Earth dynamics at normal mode frequencies. We present a method for correcting tilt on broadband ocean bottom seismometers by rotation. The correction improves the ability of some instruments to observe spheroidal modes down to 0S4. We demonstrate this method using 15 broadband ocean bottom seismometers from the PI-LAB array. We measure normal mode peak frequency shifts and compare with 1-D reference mode frequencies and predictions from 3-D global models. Our measurements agree with the 3-D models for modes between 0S14 - 0S37 with small but significant differences. These differences likely reflect real Earth structure. This suggests incorporating ocean bottom normal mode measurements into global inversions will improve models of global seismic velocity structure. 

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4. Significant ballistic thermal transport across graphene layers: Effect of nanoholes and lithium intercalation

   https://doi.org/10.1063/5.0275738  

   Crosby, John; Cui, Haoran; Wang, Yan (August 2025, Applied Physics Letters)

   Porous graphene and graphite are increasingly utilized in electrochemical energy storage and solar-thermal applications due to their unique structural and thermal properties. In this study, we conduct a comprehensive analysis of the lattice thermal transport and spectral phonon characteristics of holey graphite and multilayer graphene. Our results reveal that phonon modes propagating obliquely with respect to the graphene basal planes are the primary contributors to cross-plane thermal transport. These modes exhibit a predominantly ballistic nature, resulting in an almost linear increase in cross-plane thermal conductivity with the number of layers. The presence of nanoholes in graphene induces a broadband suppression of cross-plane phonon transport, whereas lithium-ion intercalation shows potential to enhance it. These findings provide critical insights into the mechanisms governing cross-plane heat conduction in key graphene-based structures, offering valuable guidance for thermal management and engineering of van der Waals materials. 

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5. Launching and Manipulation of Higher‐Order In‐Plane Hyperbolic Phonon Polaritons in Low‐Dimensional Heterostructures

   https://doi.org/10.1002/adma.202300301  

   Lu, Guanyu; Pan, Zhiliang; Gubbin, Christopher_R; Kowalski, Ryan_A; De_Liberato, Simone; Li, Deyu; Caldwell, Joshua_D (April 2023, Advanced Materials)

   Abstract Hyperbolic phonon polaritons (HPhPs) are stimulated by coupling infrared (IR) photons with the polar lattice vibrations. Such HPhPs offer low‐loss, highly confined light propagation at subwavelength scales with out‐of‐plane or in‐plane hyperbolic wavefronts. For HPhPs, while a hyperbolic dispersion implies multiple propagating modes with a distribution of wavevectors at a given frequency, so far it has been challenging to experimentally launch and probe the higher‐order modes that offer stronger wavelength compression, especially for in‐plane HPhPs. In this work, the experimental observation of higher‐order in‐plane HPhP modes stimulated on a 3C‐SiC nanowire (NW)/α‐MoO₃heterostructure is reported where leveraging both the low‐dimensionality and low‐loss nature of the polar NWs, higher‐order HPhPs modes within 2D α‐MoO₃crystal are launched by the 1D 3C‐SiC NW. The launching mechanism is further studied and the requirements for efficiently launching of such higher‐order modes are determined. In addition, by altering the geometric orientation between the 3C‐SiC NW and α‐MoO₃crystal, the manipulation of higher‐order HPhP dispersions as a method of tuning is demonstrated. This work illustrates an extremely anisotropic low dimensional heterostructure platform to confine and configure electromagnetic waves at the deep‐subwavelength scales for a range of IR applications including sensing, nano‐imaging, and on‐chip photonics. 

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