{"id":1470,"date":"2016-06-16T11:06:44","date_gmt":"2016-06-16T11:06:44","guid":{"rendered":"http:\/\/blogs.kent.ac.uk\/strongcorrelations\/?p=1470"},"modified":"2016-06-27T09:52:12","modified_gmt":"2016-06-27T09:52:12","slug":"laniga2-prl-2016","status":"publish","type":"post","link":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/","title":{"rendered":"Two-gap superconductivity in LaNiGa2 with non-unitary triplet pairing and even parity gap symmetry"},"content":{"rendered":"<ul class=\"kent-social-links\"><li><a href='http:\/\/www.facebook.com\/sharer.php?u=https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/&amp;t=Two-gap superconductivity in LaNiGa2 with non-unitary triplet pairing and even parity gap symmetry' target='_blank'><i class='ksocial-facebook' title='Share via Facebook'><\/i><\/a><\/li><li><a href='http:\/\/twitter.com\/home?status=Two-gap superconductivity in LaNiGa2 with non-unitary triplet pairing and even parity gap symmetry%20https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/' target='_blank'><i class='ksocial-twitter' title='Share via Twitter'><\/i><\/a><\/li><li><a href='https:\/\/plus.google.com\/share?url=https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/' target='_blank'><i class='ksocial-google-plus' title='Share via Google Plus'><\/i><\/a><\/li><li><a href='http:\/\/linkedin.com\/shareArticle?mini=true&amp;url=https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/&amp;title=Two-gap superconductivity in LaNiGa2 with non-unitary triplet pairing and even parity gap symmetry' target='_blank'><i class='ksocial-linkedin' title='Share via Linked In'><\/i><\/a><\/li><li><a href='mailto:content=https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/&amp;title=Two-gap superconductivity in LaNiGa2 with non-unitary triplet pairing and even parity gap symmetry' target='_blank'><i class='ksocial-email' title='Share via Email'><\/i><\/a><\/li><\/ul><p>Our recent joint experiment-theory paper on LaNiGa2 has just been accepted for publication in Physical Review Letters (see abstract and link to full text below). In it we present experimental data on the superconducting state of LaNiGa2 suggesting that this system has two full superconducting gaps. Interestingly, earlier work involving some of our experimental collaborators found the same behaviour (i.e. two gull gaps) in LaNiC2.<\/p>\n<figure id=\"attachment_1471\" aria-describedby=\"caption-attachment-1471\" style=\"width: 280px\" class=\"wp-caption alignright\"><a href=\"http:\/\/blogs.kent.ac.uk\/strongcorrelations\/files\/2016\/06\/Screenshot-from-2016-06-15-115903.png\" rel=\"attachment wp-att-1471\"><img loading=\"lazy\" class=\"wp-image-1471\" src=\"http:\/\/blogs.kent.ac.uk\/strongcorrelations\/files\/2016\/06\/Screenshot-from-2016-06-15-115903-150x150.png\" alt=\"Screenshot from 2016-06-15 11:59:03\" width=\"280\" height=\"250\" \/><\/a><figcaption id=\"caption-attachment-1471\" class=\"wp-caption-text\">Two distinct scenarios for two-gap superconductors: conventional two-band pairing, as in MgB2 (top) and nonunitary triplet pairing, as in LaNiC2 and LaNiGa2 (bottom).<\/figcaption><\/figure>\n<p>This is in spite of the different crystal symmetries (LaNiGa2 is centrosymmetric, while LaNiC2 is non-centrosymmetric) and very different predicted band structures and suggests a common pairing mechanism leading to two-gap behaviour and broken time-reversal symmetry. But earlier symmetry analyses suggest all BTRS states in these systems would have nodal gaps. How do we reconcile these observations?<\/p>\n<p>Our paper addresses this question by considering two distinct scenarios for two-gap superconductors: in the conventional case (see figure, top panel) intra-band pairing between electrons with opposite spins develops in two separate Fermi surfaces, leading to two distinct gaps, one on each Fermi surface. Each gap involves pairing between electrons with opposite spin directions. This is similar to MgB2, for example, and it does not involve BTRS. In our new scenario (in the bottom panel of the same figure), pairing between electrons with the same spin direction leads to a band polarisation. The two gaps thus correspond to different spin directions rather than different Fermi surfaces. That is why we always get two values of the gap, irrespectively of how many bands we started with.<\/p>\n<p>For detailed references see our paper (below).<\/p>\n<h1 class=\"title mathjax\">Two-gap superconductivity in LaNiGa<span id=\"MathJax-Element-1-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-1\" class=\"math\"><span id=\"MathJax-Span-2\" class=\"mrow\"><span id=\"MathJax-Span-3\" class=\"msubsup\"><span id=\"MathJax-Span-4\" class=\"mi\"><\/span><span id=\"MathJax-Span-5\" class=\"mn\">2<\/span><\/span><\/span><\/span><\/span> with non-unitary triplet pairing and even parity gap symmetry<\/h1>\n<div class=\"authors\"><a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Weng_Z\/0\/1\/0\/all\/0\/1\">Z. F. Weng<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Zhang_J\/0\/1\/0\/all\/0\/1\">J. L. Zhang<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Smidman_M\/0\/1\/0\/all\/0\/1\">M. Smidman<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Shang_T\/0\/1\/0\/all\/0\/1\">T. Shang<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Quintanilla_J\/0\/1\/0\/all\/0\/1\">J. Quintanilla<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Annett_J\/0\/1\/0\/all\/0\/1\">J. F. Annett<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Nicklas_M\/0\/1\/0\/all\/0\/1\">M. Nicklas<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Pang_G\/0\/1\/0\/all\/0\/1\">G. M. Pang<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Jiao_L\/0\/1\/0\/all\/0\/1\">L. Jiao<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Jiang_W\/0\/1\/0\/all\/0\/1\">W. B. Jiang<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Chen_Y\/0\/1\/0\/all\/0\/1\">Y. Chen<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Steglich_F\/0\/1\/0\/all\/0\/1\">F. Steglich<\/a>, <a href=\"http:\/\/arxiv.org\/find\/cond-mat\/1\/au:+Yuan_H\/0\/1\/0\/all\/0\/1\">H. Q. Yuan<\/a><\/div>\n<div class=\"dateline\">(Submitted on 26 May 2016)<\/div>\n<blockquote class=\"abstract mathjax\"><p>The nature of the pairing states of superconducting LaNiC<span id=\"MathJax-Element-2-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-6\" class=\"math\"><span id=\"MathJax-Span-7\" class=\"mrow\"><span id=\"MathJax-Span-8\" class=\"msubsup\"><span id=\"MathJax-Span-9\" class=\"mi\"><\/span><span id=\"MathJax-Span-10\" class=\"mn\">2<\/span><\/span><\/span><\/span><\/span> and LaNiGa<span id=\"MathJax-Element-3-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-11\" class=\"math\"><span id=\"MathJax-Span-12\" class=\"mrow\"><span id=\"MathJax-Span-13\" class=\"msubsup\"><span id=\"MathJax-Span-14\" class=\"mi\"><\/span><span id=\"MathJax-Span-15\" class=\"mn\">2<\/span><\/span><\/span><\/span><\/span> has to date remained a puzzling question. Broken time reversal symmetry has been observed in both compounds and a group theoretical analysis implies a non-unitary triplet pairing state. However all the allowed non-unitary triplet states have nodal gap functions but most thermodynamic and NMR measurements indicate fully gapped superconductivity in LaNiC<span id=\"MathJax-Element-4-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-16\" class=\"math\"><span id=\"MathJax-Span-17\" class=\"mrow\"><span id=\"MathJax-Span-18\" class=\"msubsup\"><span id=\"MathJax-Span-19\" class=\"mi\"><\/span><span id=\"MathJax-Span-20\" class=\"mn\">2<\/span><\/span><\/span><\/span><\/span>. Here we probe the gap symmetry of LaNiGa<span id=\"MathJax-Element-5-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-21\" class=\"math\"><span id=\"MathJax-Span-22\" class=\"mrow\"><span id=\"MathJax-Span-23\" class=\"msubsup\"><span id=\"MathJax-Span-24\" class=\"mi\"><\/span><span id=\"MathJax-Span-25\" class=\"mn\">2<\/span><\/span><\/span><\/span><\/span> by measuring the London penetration depth, specific heat and upper critical field. These measurements demonstrate two-gap nodeless superconductivity in LaNiGa<span id=\"MathJax-Element-6-Frame\" class=\"MathJax\"><span id=\"MathJax-Span-26\" class=\"math\"><span id=\"MathJax-Span-27\" class=\"mrow\"><span id=\"MathJax-Span-28\" class=\"msubsup\"><span id=\"MathJax-Span-29\" class=\"mi\"><\/span><span id=\"MathJax-Span-30\" class=\"mn\">2<\/span><\/span><\/span><\/span><\/span>, suggesting that this is a common feature of both compounds. These results allow us to propose a novel triplet superconducting state, where the pairing occurs between electrons of the same spin, but on different orbitals. In this case the superconducting wavefunction has a triplet spin component but isotropic even parity gap symmetry, yet the overall wavefunction remains antisymmetric under particle exchange. This model leads to a nodeless two-gap superconducting state which breaks time reversal symmetry, and therefore accounts well for the seemingly contradictory experimental results.<\/p><\/blockquote>\n<blockquote class=\"abstract mathjax\">\n<table summary=\"Additional metadata\">\n<tbody>\n<tr>\n<td class=\"tablecell label\">Comments:<\/td>\n<td class=\"tablecell comments\">5 pages, 4 figures<\/td>\n<\/tr>\n<tr>\n<td class=\"tablecell label\">Subjects:<\/td>\n<td class=\"tablecell subjects\"><span class=\"primary-subject\">Superconductivity (cond-mat.supr-con)<\/span><\/td>\n<\/tr>\n<tr>\n<td class=\"tablecell label\">Cite\u00a0as:<\/td>\n<td class=\"tablecell arxivid\"><a href=\"http:\/\/arxiv.org\/abs\/1605.08356\">arXiv:1605.08356<\/a> [cond-mat.supr-con]<\/td>\n<\/tr>\n<tr>\n<td class=\"tablecell label\"><\/td>\n<td class=\"tablecell arxividv\">(or <span class=\"arxivid\">arXiv:1605.08356v1 [cond-mat.supr-con]<\/span> for this version)<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/blockquote>\n<ul class=\"kent-social-links\"><li><a href='http:\/\/www.facebook.com\/sharer.php?u=https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/&amp;t=Two-gap superconductivity in LaNiGa2 with non-unitary triplet pairing and even parity gap symmetry' target='_blank'><i class='ksocial-facebook' title='Share via Facebook'><\/i><\/a><\/li><li><a href='http:\/\/twitter.com\/home?status=Two-gap superconductivity in LaNiGa2 with non-unitary triplet pairing and even parity gap symmetry%20https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/' target='_blank'><i class='ksocial-twitter' title='Share via Twitter'><\/i><\/a><\/li><li><a href='https:\/\/plus.google.com\/share?url=https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/' target='_blank'><i class='ksocial-google-plus' title='Share via Google Plus'><\/i><\/a><\/li><li><a href='http:\/\/linkedin.com\/shareArticle?mini=true&amp;url=https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/&amp;title=Two-gap superconductivity in LaNiGa2 with non-unitary triplet pairing and even parity gap symmetry' target='_blank'><i class='ksocial-linkedin' title='Share via Linked In'><\/i><\/a><\/li><li><a href='mailto:content=https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/&amp;title=Two-gap superconductivity in LaNiGa2 with non-unitary triplet pairing and even parity gap symmetry' target='_blank'><i class='ksocial-email' title='Share via Email'><\/i><\/a><\/li><\/ul>","protected":false},"excerpt":{"rendered":"<p>Our recent joint experiment-theory paper on LaNiGa2 has just been accepted for publication in Physical Review Letters (see abstract and link to full text below). &hellip; <a href=\"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/2016\/06\/16\/laniga2-prl-2016\/\">Read&nbsp;more<\/a><\/p>\n","protected":false},"author":976,"featured_media":1471,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":[],"categories":[54556,597],"tags":[54568,54563,54564,54567,54561,54560,54565],"_links":{"self":[{"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/posts\/1470"}],"collection":[{"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/users\/976"}],"replies":[{"embeddable":true,"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/comments?post=1470"}],"version-history":[{"count":6,"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/posts\/1470\/revisions"}],"predecessor-version":[{"id":1478,"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/posts\/1470\/revisions\/1478"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/media\/1471"}],"wp:attachment":[{"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/media?parent=1470"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/categories?post=1470"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/blogs.kent.ac.uk\/strongcorrelations\/wp-json\/wp\/v2\/tags?post=1470"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}