{"id":845,"date":"2019-10-17T16:46:06","date_gmt":"2019-10-17T16:46:06","guid":{"rendered":"https:\/\/wordpress.nkisiland.com\/?p=845"},"modified":"2019-10-17T16:46:06","modified_gmt":"2019-10-17T16:46:06","slug":"surprise-graphene-discovery-could-unlock-secrets-of-superconductivity","status":"publish","type":"post","link":"https:\/\/wordpress.nkisiland.com\/?p=845","title":{"rendered":"Surprise graphene discovery could unlock secrets of superconductivity"},"content":{"rendered":"<header class=\"article-item__header clear cleared pull--both\" style=\"font-weight: 400;color: #222222\">\n<div class=\"article__type\" style=\"font-weight: bold;color: #000000\"><strong>Physicists make misaligned sheets of the carbon material conduct electricity without resistance.\u00a0<span style=\"color: #222222\">A sandwich of two\u00a0<\/span><span style=\"color: #222222\">graphene<\/span><span style=\"color: #222222\">\u00a0layers can conduct electrons without resistance if they are twisted at a \u2018magic angle\u2019, physicists have discovered. The finding could prove to be a significant step in the decades-long search for room-temperature superconductors. (from nature.com )<\/span><\/strong><\/div>\n<\/header>\n<div class=\"clear cleared\" style=\"font-weight: 400;color: #222222\"><\/div>\n<div class=\"bordered-container clear cleared pull--both\" style=\"font-weight: 400;color: #222222\"><\/div>\n<div class=\"article__aside align-right hide-print\" style=\"font-weight: 400;color: #222222\"><\/div>\n<div class=\"align-left\" style=\"font-weight: 400;color: #222222\">\n<div class=\"article__body serif cleared\">\n<figure class=\"figure\">\n<div class=\"embed intensity--high\">\n<div class=\"embed intensity--high\"><img decoding=\"async\" loading=\"lazy\" class=\"figure__image aligncenter\" src=\"https:\/\/media.nature.com\/w800\/magazine-assets\/d41586-018-02773-w\/d41586-018-02773-w_15507794.jpg\" alt=\"3D rendering of a double layer of graphene sheets\" width=\"520\" height=\"349\" \/><\/div>\n<\/div>\n<\/figure>\n<p>Most superconductors work only at temperatures close to absolute zero. Even\u00a0\u2018high-temperature\u2019 superconductors\u00a0are called that only in a relative sense: the highest temperature at which they conduct electricity without resistance is around \u2212140 \u00baC. A material that displayed the property at room temperature \u2014 eliminating the need for expensive cooling \u2014 could revolutionize energy transmission, medical scanners and transport.<\/p>\n<p>Physicists now report that arranging two layers of atom-thick graphene so that the pattern of their carbon atoms is offset by an angle of 1.1\u00ba makes the material a superconductor. And although the system still needed to be cooled to 1.7 degrees above absolute zero, the results suggest that it may conduct electricity much like known high-temperature superconductors \u2014 and that has physicists excited. The findings are published in two\u00a0<i>Nature<\/i>\u00a0papers<a style=\"color: #006699\" href=\"https:\/\/www.nature.com\/articles\/d41586-018-02773-w#ref-CR1\">1<\/a>,<a style=\"color: #006699\" href=\"https:\/\/www.nature.com\/articles\/d41586-018-02773-w#ref-CR2\">2<\/a>\u00a0on 5 March.<\/p>\n<p>If confirmed, this discovery could be \u201cvery important\u201d to the understanding of high-temperature superconductivity, says Elena Bascones, a physicist at the Institute of Materials Science of Madrid. \u201cWe can expect a frenzy of experimental activity over the next few months to fill in the missing parts of the picture,\u201d says Robert Laughlin, a physicist and\u00a0Nobel laureate\u00a0at Stanford University in California.<\/p>\n<p>&nbsp;<\/p>\n<aside class=\"recommended pull pull--left sans-serif\"><img decoding=\"async\" loading=\"lazy\" class=\"recommended__image aligncenter\" src=\"https:\/\/media.nature.com\/w400\/magazine-assets\/d41586-018-02773-w\/d41586-018-02773-w_15510692.png\" alt=\"\" width=\"400\" height=\"300\" \/><\/p>\n<h1 class=\"recommended__title serif\" style=\"color: #1a1a1a\">News &amp; Views: Novel electronic states seen in graphene<\/h1>\n<\/aside>\n<p>Superconductors come broadly in two types: conventional, in which the activity can be explained by the mainstream theory of superconductivity, and unconventional, where it can\u2019t. The latest studies suggest that graphene\u2019s superconducting behaviour is unconventional \u2014 and has parallels with activity seen in other unconventional superconductors called cuprates. These complex copper oxides have been known to conduct electricity at up to 133 degrees above absolute zero. And although physicists have focused on cuprates for three decades in their search for room-temperature superconductors, the underlying mechanism has baffled them.<\/p>\n<p>In contrast to cuprates, the stacked graphene system is relatively simple and the material is well-understood. \u201cThe stunning implication is that cuprate superconductivity was something simple all along. It was just hard to calculate properly,\u201d says Laughlin.<\/p>\n<p><span style=\"font-weight: bolder\">Magic trick<\/span><\/p>\n<p>Graphene already has\u00a0impressive properties: its sheets, made of single layers of carbon atoms arranged in hexagons, are stronger than steel and conduct electricity better than copper. It has shown superconductivity before<a style=\"color: #006699\" href=\"https:\/\/www.nature.com\/articles\/d41586-018-02773-w#ref-CR3\">3<\/a>, but it occurred when in contact with other materials, and the behaviour could be explained by conventional superconductivity.<\/p>\n<p>Physicist Pablo Jarillo-Herrero at the Massachusetts Institute of Technology (MIT) in Cambridge and his team weren\u2019t looking for superconductivity when they set up their experiment. Instead, they were exploring how the orientation dubbed the magic angle might affect graphene. Theorists have predicted that offsetting the atoms between layers of 2D materials at this particular angle might induce the electrons that zip through the sheets to interact in interesting ways \u2014 although they didn\u2019t know exactly how.<\/p>\n<p>The team immediately saw unexpected behaviour in their two-sheet set-up. First, measurements of graphene\u2019s conductivity and the density of the particles that carry charge inside it suggested that the construction had become a Mott insulator<a style=\"color: #006699\" href=\"https:\/\/www.nature.com\/articles\/d41586-018-02773-w#ref-CR2\">2<\/a>\u00a0\u2014 a material that has all the ingredients to conduct electrons, but in which interactions between the particles stop them from flowing. Next, the researchers applied a small electric field to feed just a few extra charge carriers into the system, and it became a superconductor<a style=\"color: #006699\" href=\"https:\/\/www.nature.com\/articles\/d41586-018-02773-w#ref-CR1\">1<\/a>. The finding held up in experiment after experiment, says Jarillo-Herrero. \u201cWe have produced all of this in different devices and measured it with collaborators. This is something in which we\u2019re very confident,\u201d he says.<\/p>\n<figure class=\"figure\">\n<div class=\"embed intensity--high\">\n<div class=\"embed intensity--high\"><img decoding=\"async\" loading=\"lazy\" class=\"figure__image aligncenter\" src=\"https:\/\/media.nature.com\/w800\/magazine-assets\/d41586-018-02773-w\/d41586-018-02773-w_15507796.jpg\" alt=\"Graphene can behave as both an insulator and a superconductor\" width=\"439\" height=\"230\" \/><\/div>\n<\/div>\n<p>&nbsp;<\/p>\n<p class=\"figure__caption sans-serif\" style=\"color: #666666\"><span class=\"mr10\">A material made up of two layers of graphene, twisted at an angle of 1.1\u00ba (illustrated, right), show superconducting properties.<\/span>Courtesy of the researchers<\/p>\n<p>&nbsp;<\/p>\n<\/figure>\n<p>The existence of an insulating state so close to superconductivity is a hallmark of unconventional superconductors such as cuprates. When the researchers plotted phase diagrams that charted the material\u2019s electron density against its temperature, they saw patterns very similar to those seen for cuprates. That provides further evidence that the materials may share a superconducting mechanism, says Jarillo-Herrero.<\/p>\n<p>Finally, although graphene shows superconductivity at a very low temperature, it does so with just one-ten-thousandth of the electron density of conventional superconductors that gain the ability at the same temperature. In conventional superconductors, the phenomenon is thought to arise when vibrations allow electrons to form pairs, which stabilize their path and allow them to flow without resistance. But with so few available electrons in graphene, the fact that they can somehow pair up suggests that the interaction at play in this system should be much stronger than what happens in conventional superconductors.<\/p>\n<p><span style=\"font-weight: bolder\">Conductivity confusion<\/span><\/p>\n<p>Physicists disagree wildly on how electrons might interact in unconventional superconductors. \u201cOne of the bottlenecks of high-temperature superconductivity has been the fact that we don\u2019t understand, even now, what\u2019s really gluing the electrons into pairs,\u201d says Robinson.<\/p>\n<p>But graphene-based devices will be easier to study than cuprates, which makes them useful platforms for exploring superconductivity, says Bascones. For example, to explore the root of superconductivity in cuprates, physicists often need to subject the materials to extreme magnetic fields. And \u2018tuning\u2019 them to explore their different behaviours means growing and studying reams of different samples; with graphene, physicists can achieve the same results by simply tweaking an electric field.<\/p>\n<p>Kamran Behnia, a physicist at the Higher Institute of Industrial Physics and Chemistry in Paris, is not yet convinced that the MIT team can definitively claim to have seen the Mott insulator state, although he says the findings do suggest that graphene is a superconductor, and potentially an unusual one.<\/p>\n<p>Physicists cannot yet state with certainty that the superconducting mechanism in the two materials is the same. And Laughlin adds that it is not yet clear that all the behaviour seen in cuprates is happening in graphene. \u201cBut enough of the behaviours are present in these new experiments to give cause for cautious celebration,\u201d he says.<\/p>\n<p>Physicists have been \u201cstumbling around in the dark for 30 years\u201d trying to understand cuprates, says Laughlin. \u201cMany of us think that a light just switched on.\u201d<\/p>\n<\/div>\n<\/div>\n","protected":false},"excerpt":{"rendered":"<p>Physicists make misaligned sheets of the carbon material conduct electricity without resistance.\u00a0A sandwich of two\u00a0graphene\u00a0layers can conduct electrons without resistance if they are twisted at a \u2018magic angle\u2019, physicists have discovered. The finding could prove to be a significant step &hellip; <a href=\"https:\/\/wordpress.nkisiland.com\/?p=845\">Continue reading <span class=\"meta-nav\">&rarr;<\/span><\/a><\/p>\n","protected":false},"author":2,"featured_media":0,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[8],"tags":[],"_links":{"self":[{"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=\/wp\/v2\/posts\/845"}],"collection":[{"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=\/wp\/v2\/users\/2"}],"replies":[{"embeddable":true,"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=845"}],"version-history":[{"count":2,"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=\/wp\/v2\/posts\/845\/revisions"}],"predecessor-version":[{"id":847,"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=\/wp\/v2\/posts\/845\/revisions\/847"}],"wp:attachment":[{"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=845"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=845"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/wordpress.nkisiland.com\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=845"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}