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<jats:title>Imaging an exotic state</jats:title> <jats:p> Among the most intriguing of the many phases of cuprate superconductors is the so-called pair density wave (PDW) state. PDW is characterized by a spatially modulated density of Cooper pairs and can be detected with a scanning tunneling microscope equipped with a superconducting tip. Liu <jats:italic>et al.</jats:italic> used Josephson tunneling microscopy, modified for the task, to detect PDW in niobium diselenide, a superconductor with a layered hexagonal structure. The PDW state is expected to appear in other transition metal dichalcogenides as well. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abd4607, this issue p. <jats:related-article issue="6549" page="1447" related-article-type="in-this-issue" vol="372">1447</jats:related-article> </jats:p>

<jats:title>Easing oxygen into arenes</jats:title> <jats:p> Although oxygen is all around us, it is often surprisingly difficult to use it for selective chemical oxidations, necessitating more expensive, wasteful alternatives. Li <jats:italic>et al.</jats:italic> report that careful ligand optimization produces palladium catalysts that can efficiently activate oxygen to hydroxylate a variety of aryl and heteroaromatic rings adjacent to a carboxylic acid substituent. The ligand binds to palladium through pyridine and pyridone components, and the authors posit that tautomerization between dative and anionic coordination modes plays a role in its effectiveness. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abg2362, this issue p. <jats:related-article issue="6549" page="1452" related-article-type="in-this-issue" vol="372">1452</jats:related-article> </jats:p>

<jats:title>Stacking a ferroelectric</jats:title> <jats:p> Properties of layered van der Waals structures can depend sensitively on the stacking arrangement of constituent layers. This phenomenon has been exploited to engineer superconducting, correlated insulator, and magnetic states. Two groups now show that ferroelectricity can also be engineered through stacking: Parallel-stacked bilayers of hexagonal boron nitride exhibit ferroelectric switching even though the bulk material is not ferroelectric (see the Perspective by Tsymbal). To explore these phenomena, Yasuda <jats:italic>et al.</jats:italic> used transport measurements, whereas Vizner Stern <jats:italic>et al.</jats:italic> focused on atomic force microscopy. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abd3230 and abe8177, this issue p. <jats:related-article issue="6549" page="1458" related-article-type="in-this-issue" vol="372">1458</jats:related-article> and p. <jats:related-article issue="6549" page="1462" related-article-type="in-this-issue" vol="372">1462</jats:related-article> ; see also abi7296, p. <jats:related-article issue="6549" page="1389" related-article-type="in-this-issue" vol="372">1389</jats:related-article> </jats:p>

<jats:title>Stacking a ferroelectric</jats:title> <jats:p> Properties of layered van der Waals structures can depend sensitively on the stacking arrangement of constituent layers. This phenomenon has been exploited to engineer superconducting, correlated insulator, and magnetic states. Two groups now show that ferroelectricity can also be engineered through stacking: Parallel-stacked bilayers of hexagonal boron nitride exhibit ferroelectric switching even though the bulk material is not ferroelectric (see the Perspective by Tsymbal). To explore these phenomena, Yasuda <jats:italic>et al.</jats:italic> used transport measurements, whereas Vizner Stern <jats:italic>et al.</jats:italic> focused on atomic force microscopy. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abd3230 and abe8177, this issue p. <jats:related-article issue="6549" page="1458" related-article-type="in-this-issue" vol="372">1458</jats:related-article> and p. <jats:related-article issue="6549" page="1462" related-article-type="in-this-issue" vol="372">1462</jats:related-article> ; see also abi7296, p. <jats:related-article issue="6549" page="1389" related-article-type="in-this-issue" vol="372">1389</jats:related-article> </jats:p>

<jats:title>The making of a monolith</jats:title> <jats:p> Amorphous calcium carbonate is a hard material that is difficult to make into large, clear blocks. It is also sensitive to heating, and compacting the starting nanoparticles too much tends to lead to crystallization. Mu <jats:italic>et al.</jats:italic> determined the optimal amount of water in amorphous calcium carbonate to create clear, solid monoliths through compression. The key is to regulate the amount of diffusion in the system so that particle boundaries fuse without triggering sample-wide crystallization. This fusion strategy may also work for similar amorphous inorganic ionic compounds. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , abg1915, this issue p. <jats:related-article issue="6549" page="1466" related-article-type="in-this-issue" vol="372">1466</jats:related-article> </jats:p>