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<jats:title>A thermal signature</jats:title> <jats:p> Although the material α-ruthenium chloride exhibits some of the physics associated with Kitaev spin liquids, it is not a perfect representation of this model. Yokoi <jats:italic>et al</jats:italic> . probed the limits of the Kitaev description by studying the thermal Hall response in this material. Applying an external magnetic field both in the plane of the sample and at an angle to it, the researchers observed a half-integer quantization of the thermal Hall signal. The findings suggest the formation of a topological state consistent with the Kitaev model. —JS </jats:p>

<jats:title>Topology in higher dimensions</jats:title> <jats:p> In condensed-matter systems, the band structure of a material has often been equated with functionality. However, consideration of the topology of the band structure now provides a route to develop a functionality that goes far beyond the expected properties of the materials. Using electromagnetic metamaterials as building blocks, Ma <jats:italic>et al</jats:italic> . realized a five-dimensional generalization of a topological Weyl semimetal. Along with the three real momentum dimensions, these included two bi-anisotropy material parameters as synthetic dimensions to demonstrate both linked Weyl surfaces and Yang monopoles. The metamaterial platform provides a powerful route to explore the exotic physics associated with higher-order topological phenomena. —ISO </jats:p>

<jats:title>A reconfigurable spin ice</jats:title> <jats:p> Spin ices, magnetic systems in which local spins respect the so-called ice rules, can occur in natural materials or be engineered in patterned arrays. King <jats:italic>et al</jats:italic> . used superconducting qubits to implement a two-dimensional artificial spin ice. By changing the strength and ratio of spin couplings, the researchers were able to access a variety of ground states. Arranging the boundary spins in an antiferromagnetic configuration and then flipping one of those spins generated a magnetic monopole in the system’s interior. —JS </jats:p>

<jats:title>What makes familiar faces so special?</jats:title> <jats:p> Explicit semantic information in the brain is generated by gradually stripping off the specific context in which the item is embedded. A particularly striking example of such explicit representations are face-specific neurons. Landi <jats:italic>et al</jats:italic> . report the properties of neurons in a small region of the monkey anterior temporal cortex that respond to the sight of familiar faces. These cells respond to the internal features of familiar faces but not unknown faces. Some of these responses are very highly selective, reliably responding to only one face out of a vast number of other stimuli. These findings will advance our understanding about where and how semantic memories are stored in the brain. —PRS </jats:p>

<jats:title>Plant cell growth regulation</jats:title> <jats:p> Piezo sensors in animal cells are localized in the cell membrane and transduce mechanical signals. The cell membrane of plant cells, unlike that of animal cells, is usually plastered up against a stiff cell wall and does not have much mobility. Much of the cell’s volume is accounted for by a large central vacuole, the membrane of which, the tonoplast, is not so mechanically constrained. Radin <jats:italic>et al</jats:italic> . studied how and where plant cells use Piezo sensors. Plant homologs of the animal mechanosensitive channels are found not in the plasma membrane but rather in the tonoplast. In both moss and the small flowering plant <jats:italic>Arabidopsis</jats:italic> , mutations in plant Piezo sensors altered vacuolar morphology and growth patterns in tip-growing cells. —PJH </jats:p>

<jats:p>A weekly roundup of information on newly offered instrumentation, apparatus, and laboratory materials of potential interest to researchers.</jats:p>

<jats:title>SARS-CoV-2 from alpha to epsilon</jats:title> <jats:p> As battles to contain the COVID-19 pandemic continue, attention is focused on emerging variants of the severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) virus that have been deemed variants of concern because they are resistant to antibodies elicited by infection or vaccination or they increase transmissibility or disease severity. Three papers used functional and structural studies to explore how mutations in the viral spike protein affect its ability to infect host cells and to evade host immunity. Gobeil <jats:italic>et al</jats:italic> . looked at a variant spike protein involved in transmission between minks and humans, as well as the B1.1.7 (alpha), B.1.351 (beta), and P1 (gamma) spike variants; Cai <jats:italic>et al</jats:italic> . focused on the alpha and beta variants; and McCallum <jats:italic>et al</jats:italic> . discuss the properties of the spike protein from the B1.1.427/B.1.429 (epsilon) variant. Together, these papers show a balance among mutations that enhance stability, those that increase binding to the human receptor ACE2, and those that confer resistance to neutralizing antibodies. —VV </jats:p>

<jats:title>Advances in colloidal quantum dots</jats:title> <jats:p> The confinement found in colloidal semiconductor quantum dots enables the design of materials with tunable properties. García de Arquer <jats:italic>et al</jats:italic> . review the recent advances in methods for synthesis and surface functionalization of quantum dots that enable fine tuning of their optical, chemical, and electrical properties. These important developments have driven the commercialization of display and lighting applications and provide promising developments in the related fields of lasing and sensing. —MSL </jats:p>