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1. Wind-Forced Seasonal Exchange between Marginal Seas and the Open Ocean

   https://doi.org/10.1175/JPO-D-22-0151.1  

   Spall, Michael A. ( March 2023 , Journal of Physical Oceanography)

   The circulation within marginal seas subject to periodic winds, and their exchange with the open ocean, are explored using idealized numerical models and theory. This is motivated by the strong seasonal cycle in winds over the Nordic Seas and the exchange with the subpolar North Atlantic Ocean through the Denmark Strait and Faroe Bank Channel. Two distinct regimes are identified: an interior with closedf/hcontours and a shallow shelf region that connects to the open ocean. The interior develops a strong oscillating along-topography circulation with weaker ageostrophic radial flows. The relative importance of the bottom Ekman layer and interior ageostrophic flows depends only onωh/C_d, whereωis the forcing frequency,his the bottom depth, andC_dis a linear bottom drag coefficient. The dynamics on the shelf are controlled by the frictional decay of coastal waves over an along-shelf scaleL_y=f₀L_sH_s/C_d, wheref₀is the Coriolis parameter, andL_sandH_sare the shelf width and depth. ForL_ymuch less than the perimeter of the basin, the surface Ekman transport is provided primarily by overturning within the marginal sea and there is little exchange with the open ocean. ForL_yon the order of the basin perimeter or larger, most of the Ekman transport is provided from outside the marginal sea with an opposite exchange through the deep part of the strait. This demonstrates a direct connection between the dynamics of coastal waves on the shelf and the exchange of deep waters through the strait, some of which is derived from below sill depth.

   The purpose of this study is to understand how winds over marginal seas, which are semienclosed bodies of water around the perimeter of ocean basins, can force an exchange of water, heat, salt, and other tracers through narrow straits between the marginal sea and the open ocean. Understanding this exchange is important because marginal seas are often regions of net heat, freshwater, and carbon exchange with the atmosphere. The present results identify a direct connection between processes along the coast of the marginal sea and the flow of waters through deep straits into the open ocean.

    

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2. Competing Heat Carriers Leading to Distinctive Cation Concentration Dependent Thermal Conductivity of Amorphous Li x S ( x  = 0–2) Batteries

   https://doi.org/10.1002/adfm.202214501  

   Gao, Yufei ; Fan, Hongzhao ; Zhou, Yanguang ; Hu, Ming ( April 2023 , Advanced Functional Materials)

   Thermal transport in amorphous lithium‐sulfur (a‐Li_xS) is systematically investigated using molecular dynamics and the contributions from different types of heat carriers are quantitatively evaluated. In general, the thermal conductivity (TC) ofa‐Li_xS changes largely by varying the concentration (x) of Li ions ina‐Li_xS. Interestingly, the TC ofa‐Li_xS shows three distinct regimes of dependence on Li concentration. For low Li concentration (x = 0.4–1.2), the TC grows slowly, followed by a rapid increase in TC for medium Li concentration (x = 1.2–1.6), where the growth rate is three times that of the first regime, and finally, the TC is independent of Li concentration (x = 1.6–2.0). The TC enhancement in the first and second regimes is mainly attributed to propagating and non‐propagating vibrational modes ina‐Li_xS, respectively. In contrast, the stable thermal transport regime is governed by the competition between propagating and non‐propagating phonons. These investigations provide quantitative TC data of various polysulfides for shuttling analysis, and a fundamental understanding of the thermal transport mechanism of complexa‐Li_xS structures, which is beneficial for the rational design of thermal management of Li‐S batteries.

    

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3. Evidence for one-dimensional chiral edge states in a magnetic Weyl semimetal Co3Sn2S2

   https://doi.org/10.1038/s41467-021-24561-3  

   Howard, Sean ; Jiao, Lin ; Wang, Zhenyu ; Morali, Noam ; Batabyal, Rajib ; Kumar-Nag, Pranab ; Avraham, Nurit ; Beidenkopf, Haim ; Vir, Praveen ; Liu, Enke ; et al ( July 2021 , Nature Communications)

   The physical realization of Chern insulators is of fundamental and practical interest, as they are predicted to host the quantum anomalous Hall (QAH) effect and topologically protected chiral edge states which can carry dissipationless current. Current realizations of the QAH state often require complex heterostructures and sub-Kelvin temperatures, making the discovery of intrinsic, high temperature QAH systems of significant interest. In this work we show that time-reversal symmetry breaking Weyl semimetals, being essentially stacks of Chern insulators with inter-layer coupling, may provide a new platform for the higher temperature realization of robust chiral edge states. We present combined scanning tunneling spectroscopy and theoretical investigations of the magnetic Weyl semimetal, Co₃Sn₂S₂. Using modeling and numerical simulations we find that depending on the strength of the interlayer coupling, chiral edge states can be localized on partially exposed kagome planes on the surfaces of a Weyl semimetal. Correspondingly, our dI/dVmaps on the kagome Co₃Sn terraces show topological states confined to the edges which display linear dispersion. This work provides a new paradigm for realizing chiral edge modes and provides a pathway for the realization of higher temperature QAH effect in magnetic Weyl systems in the two-dimensional limit.

    

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4. Materials selection rules for optimum power factor in two-dimensional thermoelectrics

   https://doi.org/10.1088/2515-7639/ab4600  

   Kommini, Adithya ; Aksamija, Zlatan ( November 2019 , Journal of Physics: Materials)

   Two-dimensional (2D) materials have emerged as the ideal candidates for many applications, including nanoelectronics, low-power devices, and sensors. Several 2D materials have been shown to possess large Seebeck coefficients, thus making them suitable for thermoelectric (TE) energy conversion. Whether even higher TE power factors can be discovered among the ≈2000 possible 2D materials (Mounetet al2018Nat. Nanotechnol.13246–52) is an open question. This study aims at formulating selection rules to guide the search for superior 2D TE materials without the need for expensive atomistic simulations. We show that a 2D material having a combination of low effective mass, higher separation in the height of the step-like density of states, and valley splitting, which is the energy difference between the bottom of conduction band and the satellite valley, equal to 5k_BTwill lead to a higher TE power factor. Further, we find that inelastic scattering with optical phonons plays a significant role: if inelastic scattering is the dominant mechanism and the energy of the optical phonon equals 5k_BT, then the TE power factor is maximized. Starting from a model for carrier transport in MoS₂and progressively introducing the aforementioned features results in a two-orders-of-magnitude improvement in the power factor. Compared to the existing selection rules or material descriptors, features identified in this study provide the ability to comprehensively evaluate TE capability of a material and helps in identifying future TE materials suitable for applications in waste-heat scavenging, thermal sensors, and nanoelectronics cooling.

    

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5. How heat propagates in liquid 3He

   https://doi.org/10.1038/s41467-024-46079-0  

   Behnia, Kamran ; Trachenko, Kostya ( February 2024 , Nature Communications)

   In Landau’s Fermi liquid picture, transport is governed by scattering between quasi-particles. The normal liquid³He conforms to this picture but only at very low temperature. Here, we show that the deviation from the standard behavior is concomitant with the fermion-fermion scattering time falling below the Planckian time,$$\frac{\hslash }{{k}_{{{{{{{{\rm{B}}}}}}}}}T}$$$\frac{\hslash }{k_{B}T}$and the thermal diffusivity of this quantum liquid is bounded by a minimum set by fundamental physical constants and observed in classical liquids. This points to collective excitations (a sound mode) as carriers of heat. We propose that this mode has a wavevector of 2k_Fand a mean free path equal to the de Broglie thermal length. This would provide an additional conducting channel with aT ^1/2temperature dependence, matching what is observed by experiments. The experimental data from 0.007 K to 3 K can be accounted for, with a margin of 10%, if thermal conductivity is the sum of two contributions: one by quasi-particles (varying as the inverse of temperature) and another by sound (following the square root of temperature).

    

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