Zheng Li, Chao Mu, Pengfei Li, Wei Wu, Jiangping Hu, Tao Xiang, Kun Jiang, Jianlin Luo
{"title":"Unconventional Coherence Peak in Cuprate Superconductors","authors":"Zheng Li, Chao Mu, Pengfei Li, Wei Wu, Jiangping Hu, Tao Xiang, Kun Jiang, Jianlin Luo","doi":"10.1103/physrevx.14.041072","DOIUrl":null,"url":null,"abstract":"The Hebel-Slichter coherence peak, observed in the spin-lattice relaxation rate 1</a:mn>/</a:mo>T</a:mi>1</a:mn></a:msub></a:math> just below the critical temperature <c:math xmlns:c=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><c:msub><c:mi>T</c:mi><c:mi mathvariant=\"normal\">c</c:mi></c:msub></c:math>, serves as a crucial experimental validation of the Bardeen-Cooper-Schrieffer pairing symmetry in conventional superconductors. However, no coherence peak in <f:math xmlns:f=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><f:mn>1</f:mn><f:mo>/</f:mo><f:msub><f:mi>T</f:mi><f:mn>1</f:mn></f:msub></f:math> has been observed in unconventional superconductors like cuprates. In this study, an unconventional coherence peak is identified for the first time using nuclear quadrupole resonance on <h:math xmlns:h=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><h:mrow><h:msub><h:mrow><h:mi>YBa</h:mi></h:mrow><h:mrow><h:mn>2</h:mn></h:mrow></h:msub><h:msub><h:mrow><h:mi>Cu</h:mi></h:mrow><h:mrow><h:mn>4</h:mn></h:mrow></h:msub><h:msub><h:mrow><h:mi mathvariant=\"normal\">O</h:mi></h:mrow><h:mrow><h:mn>8</h:mn></h:mrow></h:msub></h:mrow></h:math>, pointing to a distinctive pairing symmetry. The spin-lattice relaxation rate in nuclear quadrupole resonance and nuclear magnetic resonance with nuclear spin <k:math xmlns:k=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><k:mi>I</k:mi><k:mo>></k:mo><k:mn>1</k:mn><k:mo>/</k:mo><k:mn>2</k:mn></k:math> comprises the magnetic relaxation rate <m:math xmlns:m=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><m:mn>1</m:mn><m:mo>/</m:mo><m:msubsup><m:mi>T</m:mi><m:mn>1</m:mn><m:mi>mag</m:mi></m:msubsup></m:math>, which probes magnetic fluctuations, and the quadrupole relaxation rate <o:math xmlns:o=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><o:mn>1</o:mn><o:mo>/</o:mo><o:msubsup><o:mi>T</o:mi><o:mn>1</o:mn><o:mrow><o:mi>quad</o:mi></o:mrow></o:msubsup></o:math>, which probes charge fluctuations. By utilizing <q:math xmlns:q=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><q:mrow><q:mmultiscripts><q:mrow><q:mi>Cu</q:mi></q:mrow><q:mprescripts/><q:none/><q:mrow><q:mn>63</q:mn></q:mrow></q:mmultiscripts></q:mrow></q:math> and <s:math xmlns:s=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><s:mrow><s:mmultiscripts><s:mrow><s:mi>Cu</s:mi></s:mrow><s:mprescripts/><s:none/><s:mrow><s:mn>65</s:mn></s:mrow></s:mmultiscripts></s:mrow></s:math> isotopes, we successfully distinguish <u:math xmlns:u=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><u:mn>1</u:mn><u:mo>/</u:mo><u:msubsup><u:mi>T</u:mi><u:mn>1</u:mn><u:mi>mag</u:mi></u:msubsup></u:math> and <w:math xmlns:w=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><w:mn>1</w:mn><w:mo>/</w:mo><w:msubsup><w:mi>T</w:mi><w:mn>1</w:mn><w:mrow><w:mi>quad</w:mi></w:mrow></w:msubsup></w:math> of <y:math xmlns:y=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><y:mrow><y:msub><y:mrow><y:mi>YBa</y:mi></y:mrow><y:mrow><y:mn>2</y:mn></y:mrow></y:msub><y:msub><y:mrow><y:mi>Cu</y:mi></y:mrow><y:mrow><y:mn>4</y:mn></y:mrow></y:msub><y:msub><y:mrow><y:mi mathvariant=\"normal\">O</y:mi></y:mrow><y:mrow><y:mn>8</y:mn></y:mrow></y:msub></y:mrow></y:math> and reveal the presence of the coherence peak in <bb:math xmlns:bb=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><bb:mn>1</bb:mn><bb:mo>/</bb:mo><bb:msubsup><bb:mi>T</bb:mi><bb:mn>1</bb:mn><bb:mrow><bb:mi>quad</bb:mi></bb:mrow></bb:msubsup></bb:math> but not in <db:math xmlns:db=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><db:mn>1</db:mn><db:mo>/</db:mo><db:msubsup><db:mi>T</db:mi><db:mn>1</db:mn><db:mi>mag</db:mi></db:msubsup></db:math>, in contrast to conventional superconductors. Our finding demonstrates that unconventional superconductors do not exhibit a coherence peak in <fb:math xmlns:fb=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><fb:mn>1</fb:mn><fb:mo>/</fb:mo><fb:msub><fb:mi>T</fb:mi><fb:mn>1</fb:mn></fb:msub></fb:math> when the relaxation is due to fluctuations of the hyperfine field. Conversely, a coherence peak is expected when the relaxation is caused by electric field gradient fluctuations, due to the different coherence factors between charge and magnetic fluctuations. Our successful measurements of <hb:math xmlns:hb=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><hb:mrow><hb:mn>1</hb:mn><hb:mo>/</hb:mo><hb:msub><hb:mrow><hb:mi>T</hb:mi></hb:mrow><hb:mrow><hb:mn>1</hb:mn></hb:mrow></hb:msub></hb:mrow></hb:math> for the chains of <jb:math xmlns:jb=\"http://www.w3.org/1998/Math/MathML\" display=\"inline\"><jb:mrow><jb:msub><jb:mrow><jb:mi>YBa</jb:mi></jb:mrow><jb:mrow><jb:mn>2</jb:mn></jb:mrow></jb:msub><jb:msub><jb:mrow><jb:mi>Cu</jb:mi></jb:mrow><jb:mrow><jb:mn>4</jb:mn></jb:mrow></jb:msub><jb:msub><jb:mrow><jb:mi mathvariant=\"normal\">O</jb:mi></jb:mrow><jb:mrow><jb:mn>8</jb:mn></jb:mrow></jb:msub></jb:mrow></jb:math> suggest that, should the conditions for predominant quadrupole relaxation be satisfied, this phenomenon could provide a novel approach to exploring the unconventional nature of the pairing mechanism in other superconductors. <jats:supplementary-material> <jats:copyright-statement>Published by the American Physical Society</jats:copyright-statement> <jats:copyright-year>2024</jats:copyright-year> </jats:permissions> </jats:supplementary-material>","PeriodicalId":20161,"journal":{"name":"Physical Review X","volume":"26 1","pages":""},"PeriodicalIF":11.6000,"publicationDate":"2024-12-31","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Physical Review X","FirstCategoryId":"101","ListUrlMain":"https://doi.org/10.1103/physrevx.14.041072","RegionNum":1,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"PHYSICS, MULTIDISCIPLINARY","Score":null,"Total":0}
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Abstract
The Hebel-Slichter coherence peak, observed in the spin-lattice relaxation rate 1/T1 just below the critical temperature Tc, serves as a crucial experimental validation of the Bardeen-Cooper-Schrieffer pairing symmetry in conventional superconductors. However, no coherence peak in 1/T1 has been observed in unconventional superconductors like cuprates. In this study, an unconventional coherence peak is identified for the first time using nuclear quadrupole resonance on YBa2Cu4O8, pointing to a distinctive pairing symmetry. The spin-lattice relaxation rate in nuclear quadrupole resonance and nuclear magnetic resonance with nuclear spin I>1/2 comprises the magnetic relaxation rate 1/T1mag, which probes magnetic fluctuations, and the quadrupole relaxation rate 1/T1quad, which probes charge fluctuations. By utilizing Cu63 and Cu65 isotopes, we successfully distinguish 1/T1mag and 1/T1quad of YBa2Cu4O8 and reveal the presence of the coherence peak in 1/T1quad but not in 1/T1mag, in contrast to conventional superconductors. Our finding demonstrates that unconventional superconductors do not exhibit a coherence peak in 1/T1 when the relaxation is due to fluctuations of the hyperfine field. Conversely, a coherence peak is expected when the relaxation is caused by electric field gradient fluctuations, due to the different coherence factors between charge and magnetic fluctuations. Our successful measurements of 1/T1 for the chains of YBa2Cu4O8 suggest that, should the conditions for predominant quadrupole relaxation be satisfied, this phenomenon could provide a novel approach to exploring the unconventional nature of the pairing mechanism in other superconductors. Published by the American Physical Society2024
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Physical Review X (PRX) stands as an exclusively online, fully open-access journal, emphasizing innovation, quality, and enduring impact in the scientific content it disseminates. Devoted to showcasing a curated selection of papers from pure, applied, and interdisciplinary physics, PRX aims to feature work with the potential to shape current and future research while leaving a lasting and profound impact in their respective fields. Encompassing the entire spectrum of physics subject areas, PRX places a special focus on groundbreaking interdisciplinary research with broad-reaching influence.
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