Catálogo de publicaciones - revistas

<jats:title>Making a large-gap topological insulator</jats:title> <jats:p> Although of interest to basic research, topological insulators (TIs) have not yet lived up to their technological potential. This is partly because their protected surface-edge state usually lives within a narrow energy gap, with its exotic transport properties overwhelmed by the ordinary bulk material. Reis <jats:italic>et al.</jats:italic> show that a judicious choice of materials can make the gap wide enough for the topological properties to be apparent at room temperature. Numerical calculations indicate that a monolayer of Bismuth grown on SiC(0001) is a two-dimensional TI with a large energy gap. The researchers fabricated such a heterostructure and characterized it using scanning tunneling spectroscopy. The size of the experimentally measured gap was consistent with the calculations. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="287" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aai8142">287</jats:related-article> </jats:p>

<jats:title>Volcanoes find a new carbon platform</jats:title> <jats:p> The geological carbon cycle assumes that carbon is emitted by volcanic eruptions and removed through various forms of burial. Mason <jats:italic>et al.</jats:italic> found that not all volcanic eruptions have the same source for carbon in their volcanic gas. Arc volcanic activity appears to harvest carbon from old carbonate platforms, which results in a massive difference in the isotopic signature of the carbon emitted during eruption. This discovery requires revision of the global carbon cycle, decreasing the amount of organic carbon believed to be being buried. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="290" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aan5049">290</jats:related-article> </jats:p>

<jats:title>A propagating Majorana mode</jats:title> <jats:p> Although Majorana fermions remain elusive as elementary particles, their solid-state analogs have been observed in hybrid semiconductor-superconductor nanowires. In a nanowire setting, the Majorana states are localized at the ends of the wire. He <jats:italic>et al.</jats:italic> built a two-dimensional heterostructure in which a one-dimensional Majorana mode is predicted to run along the sample edge (see the Perspective by Pribiag). The heterostructure consisted of a quantum anomalous Hall insulator (QAHI) bar contacted by a superconductor. The authors used an external magnetic field as a “knob” to tune into a regime where a Majorana mode was propagating along the edge of the QAHI bar covered by the superconductor. A signature of this propagation—half-quantized conductance—was then observed in transport experiments. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="294" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aag2792">294</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="252" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aao0793">252</jats:related-article> </jats:p>

<jats:title>Pulling on bonds counterintuitively</jats:title> <jats:p> Experimental mechanochemistry has largely focused on the application of force along chemical bonds to accelerate their cleavage. Akbulatov <jats:italic>et al.</jats:italic> now demonstrate that force can also play a more subtle role. They generated strained macrocyclic rings photochemically and then studied the influence of that strain on the rates of reactions that cleaved either phosphorus-oxygen or silicon-oxygen bonds. P-O cleavage was accelerated by force orthogonal to the bond axis, whereas the Si-O cleavage was inhibited by force along the bond. Both results were consistent with the respective transition states predicted by theory. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="299" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aan1026">299</jats:related-article> </jats:p>

<jats:title>Hitting the highs in solid state</jats:title> <jats:p> The ability to generate high harmonics of optical frequencies through the nonlinear interaction between intense light pulses and gas atoms has opened up the area of ultrafast optics and spectroscopy. Sivis <jats:italic>et al.</jats:italic> now show that high harmonics can also be generated with a solid-state sample. They used nanofabricated structured targets of ZnO and varied the chemical composition of the sample to demonstrate that (modest) high harmonics can be generated as the light interacts with the target materials. The results present the possibility of developing solid-state ultrafast optical devices. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="303" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aan2395">303</jats:related-article> </jats:p>

<jats:title>Finding a more flexible mechanical sensor</jats:title> <jats:p> Piezoelectric materials allow conversion between electricity and mechanical stresses. The most efficient piezoelectric materials are ceramics such as BaTiO <jats:sub>3</jats:sub> or PbZrO <jats:sub>3</jats:sub> , which are also extremely stiff. You <jats:italic>et al.</jats:italic> identified an organic perovskite structured piezoelectric material that is far more pliable yet has a piezoelectric response similar to that of traditional ceramics. This material may be a better option to use as a mechanical sensor for flexible devices, soft robotics, biomedical devices, and other micromechanical applications that benefit from a less stiff piezoelectric material. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="306" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aai8535">306</jats:related-article> </jats:p>

<jats:title>Hydraulic fins</jats:title> <jats:p> The lymphatic system in fish has much the same function as it does in mammals—immune response and homeostasis. Pavlov <jats:italic>et al.</jats:italic> show, however, that in the scromboid (tuna and mackerel) family of fish, this fluid homeostasis function has been co-opted to help facilitate dorsal fin rigidity and movement (see the Perspective by Triantafyllou). In bluefin tuna, a series of lymphatic vessels are integrated with muscles that allow the fish to raise and stiffen their dorsal fin. This provides extra stability during swimming. </jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="310" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aak9607">310</jats:related-article> ; see also p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="251" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aan8354">251</jats:related-article> </jats:p>

<jats:title>Getting loaded—make mine a double!</jats:title> <jats:p>Chromosomal DNA replication initiates bidirectionally by loading two ring-shaped helicases onto DNA in opposite orientations. How this symmetry is achieved has been puzzling because replication initiation sites contain only one essential binding site for the initiator, the origin recognition complex (ORC). Coster and Diffley now show that both helicases are loaded by a similar mechanism. Efficient loading requires binding of two ORC complexes to two ORC binding sites in opposite orientations. Natural origins were found to be partially symmetrical, containing functionally relevant secondary ORC sites. Sites can be flexibly spaced, but introducing an intervening “roadblock” prevented loading, suggesting that individual helicases translocate toward each other on DNA to form a stable double ring.</jats:p> <jats:p> <jats:italic>Science</jats:italic> , this issue p. <jats:related-article xmlns:xlink="http://www.w3.org/1999/xlink" ext-link-type="doi" issue="6348" page="314" related-article-type="in-this-issue" vol="357" xlink:href="10.1126/science.aan0063">314</jats:related-article> </jats:p>

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