{"id":4851,"date":"2019-08-05T20:46:06","date_gmt":"2019-08-06T03:46:06","guid":{"rendered":"http:\/\/physikon.net\/?p=4851"},"modified":"2022-06-22T09:36:53","modified_gmt":"2022-06-22T16:36:53","slug":"high-tc-superconductivity-originating-from-interlayer-coulomb-coupling-in-gate-charged-twisted-bilayer-graphene-moire-superlattices","status":"publish","type":"post","link":"http:\/\/physikon.net\/?p=4851","title":{"rendered":"High-Tc<\/sub> Superconductivity Originating from Interlayer Coulomb Coupling in Gate-Charged Twisted Bilayer Graphene Moir\u00e9 Superlattices"},"content":{"rendered":"

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High-T<\/i>C<\/sub> Superconductivity Originating from Interlayer Coulomb Coupling in Gate-Charged Twisted Bilayer Graphene Moir\u00e9 Superlattices<\/strong>, D. R. Harshman and A. T. Fiory\u00a0[arXiv<\/a>]\n

Unconventional superconductivity in bilayer graphene has been reported for twist angles \u03b8 near the first magic angle and charged electrostatically with holes near half filling of the lower flat bands. A maximum superconducting transition temperature\u00a0T<\/em>C<\/sub>\u2009\u2248\u20091.7\u00a0K was reported for a device with \u03b8\u2009=\u20091.05\u00b0 at ambient pressure and a maximum\u00a0T<\/em>C<\/sub>\u2009\u2248\u20093.1\u00a0K for a device with \u03b8\u2009=\u20091.27\u00b0 under 1.33\u00a0GPa hydrostatic pressure. A high-T<\/em>C<\/sub>\u00a0model for the superconductivity is proposed herein, where pairing is mediated by Coulomb coupling between charges in the two graphene sheets. The expression derived for the optimal transition temperature,\u00a0T<\/em>C0<\/sub>\u2009=\u2009k<\/em>B<\/sub>\u22121<\/sup>\u039b(|n<\/em>opt<\/sub>\u2009\u2212\u2009n<\/em>0<\/sub>|\/2)1\/2<\/sup>e<\/em>2<\/sup>\/\u03b6, is a function of mean bilayer separation distance \u03b6, measured gated charge areal densities\u00a0n<\/em>opt<\/sub>\u00a0and\u00a0n<\/em>0<\/sub>\u00a0corresponding to maximum\u00a0T<\/em>C<\/sub>\u00a0and superconductivity onset, respectively, and the length constant \u039b\u2009=\u20090.00747(2) \u00c5. Based on existing experimental carrier densities and theoretical estimates for \u03b6,\u00a0T<\/em>C0<\/sub>\u2009=\u20091.94(4) K is calculated for the \u03b8\u2009=\u20091.05\u00b0 ambient-pressure device and\u00a0T<\/em>C0<\/sub>\u2009=\u20093.02(3) K for the \u03b8\u2009=\u20091.27\u00b0 pressurized device. Experimental mean-field transition temperatures\u00a0T<\/em>C<\/sub>mf<\/sup>\u2009=\u20091.83(5) K and\u00a0T<\/em>C<\/sub>mf<\/sup>\u2009=\u20092.86(5) K are determined by fitting superconducting fluctuation theory to resistance transition data for the ambient-pressure and pressurized devices, respectively; the theoretical results for\u00a0T<\/em>C0<\/sub>\u00a0are in remarkable agreement with these experimental values. Corresponding Berezinskii-Kosterlitz-Thouless temperatures\u00a0T<\/em>BKT<\/sub>\u00a0of 0.96(3) K and 2.2(2) K are also determined and interpreted.<\/p>\n\n\n

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T<\/em>C0<\/sub>meas<\/sup> versus (\u2113\u03b6)\u20131<\/sup> for TBG devices M2 and D2 (two square symbols) compared to 51 other optimal high-T<\/em>C<\/sub> superconductors: cuprates and ruthenates; iron pnictides and chalcogenides; intercalated group-4-metal nitride-chlorides; and other organics. The black solid line represents T<\/em>C0<\/sub>. Inset shows the distribution (histogram bin width 0.02) of the fractional difference (T<\/em>C0<\/sub>calc<\/sup> \u2013 T<\/em>C0<\/sub>meas<\/sup>)\/T<\/em>C0<\/sub>meas<\/sup> for the 53 optimal high-T<\/em>C<\/sub> superconductors, including TBG devices M2 and D2. A fitted normal distribution (dashed curve) is provided for comparison.<\/p><\/figcaption><\/figure>\n\n\n\n

Dale R. Harshman and Anthony T. Fiory, Journal of Superconductivity and Novel Magnetism 33<\/strong>, 367 (2020)<\/a>.<\/p>\n","protected":false},"excerpt":{"rendered":"<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[9,8,28],"tags":[],"class_list":["post-4851","post","type-post","status-publish","format-standard","hentry","category-high-tc-superconductivity","category-high-tc-theory","category-transition-temperature"],"_links":{"self":[{"href":"http:\/\/physikon.net\/index.php?rest_route=\/wp\/v2\/posts\/4851","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/physikon.net\/index.php?rest_route=\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/physikon.net\/index.php?rest_route=\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/physikon.net\/index.php?rest_route=\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"http:\/\/physikon.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcomments&post=4851"}],"version-history":[{"count":19,"href":"http:\/\/physikon.net\/index.php?rest_route=\/wp\/v2\/posts\/4851\/revisions"}],"predecessor-version":[{"id":7690,"href":"http:\/\/physikon.net\/index.php?rest_route=\/wp\/v2\/posts\/4851\/revisions\/7690"}],"wp:attachment":[{"href":"http:\/\/physikon.net\/index.php?rest_route=%2Fwp%2Fv2%2Fmedia&parent=4851"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/physikon.net\/index.php?rest_route=%2Fwp%2Fv2%2Fcategories&post=4851"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/physikon.net\/index.php?rest_route=%2Fwp%2Fv2%2Ftags&post=4851"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}