{"title":"Cascade of strongly correlated quantum states in a partially filled kagome flat band","authors":"Caiyun Chen, Jiangchang Zheng, Yuman He, Xuzhe Ying, Soumya Sankar, Luanjing Li, Yizhou Wei, Xi Dai, Hoi Chun Po, Berthold Jäck","doi":"arxiv-2409.06933","DOIUrl":null,"url":null,"abstract":"Coulomb interactions among charge carriers that occupy an electronic flat\nband have a profound impact on the macroscopic properties of materials. At\nsufficient strength, these interactions can give rise to captivating phenomena\nsuch as quantum criticality, Mott-Hubbard states, and unconventional\nsuperconductivity. The appearance of these characteristics sensitively depends\non the number of electrons occupying the flat band states. In this work, we\npresent experimental evidence obtained from scanning tunneling microscopy\nmeasurements for a cascade of strongly correlated states appearing in the\npartially occupied kagome flat bands of Co$_{1-x}$Fe$_x$Sn whose filling can be\ncontrolled by the Fe-doping level $x$. At elevated temperatures ($T\\geq16\\,K$),\nwe detect a nematic electronic state across a broad doping range $0.05<x<0.25$.\nThe comparison with model calculations reveals that strong Coulomb interactions\n($U>100\\,$meV) blend the states of two $3d$-orbital derived flat bands and\nimpart a nematic order parameter. This state serves as the parent phase of a\nstrongly correlated phase diagram: At lower temperatures $T<16\\,$K, we find\nspectroscopic evidence for an orbital-selective Mott state enabled by the\n$3d$-orbital degeneracy of the Co atom. This state can only be detected in\nsamples with ideal Fe doping ($x=0.17$) and descends into pseudogap phases upon\nelectron and hole doping. At $T<8\\,$K, the pseudogap phase evolves into another\nnematic low temperature state. Our observations demonstrate that the electronic\nground state of a kagome flat band depends on the complex interplay between\nstrong Coulomb repulsion, $3d$-orbital degeneracy, and flat band filling\nfraction at different temperatures.","PeriodicalId":501171,"journal":{"name":"arXiv - PHYS - Strongly Correlated Electrons","volume":"21 1","pages":""},"PeriodicalIF":0.0000,"publicationDate":"2024-09-11","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"arXiv - PHYS - Strongly Correlated Electrons","FirstCategoryId":"1085","ListUrlMain":"https://doi.org/arxiv-2409.06933","RegionNum":0,"RegionCategory":null,"ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"","JCRName":"","Score":null,"Total":0}
引用次数: 0
Abstract
Coulomb interactions among charge carriers that occupy an electronic flat
band have a profound impact on the macroscopic properties of materials. At
sufficient strength, these interactions can give rise to captivating phenomena
such as quantum criticality, Mott-Hubbard states, and unconventional
superconductivity. The appearance of these characteristics sensitively depends
on the number of electrons occupying the flat band states. In this work, we
present experimental evidence obtained from scanning tunneling microscopy
measurements for a cascade of strongly correlated states appearing in the
partially occupied kagome flat bands of Co$_{1-x}$Fe$_x$Sn whose filling can be
controlled by the Fe-doping level $x$. At elevated temperatures ($T\geq16\,K$),
we detect a nematic electronic state across a broad doping range $0.05100\,$meV) blend the states of two $3d$-orbital derived flat bands and
impart a nematic order parameter. This state serves as the parent phase of a
strongly correlated phase diagram: At lower temperatures $T<16\,$K, we find
spectroscopic evidence for an orbital-selective Mott state enabled by the
$3d$-orbital degeneracy of the Co atom. This state can only be detected in
samples with ideal Fe doping ($x=0.17$) and descends into pseudogap phases upon
electron and hole doping. At $T<8\,$K, the pseudogap phase evolves into another
nematic low temperature state. Our observations demonstrate that the electronic
ground state of a kagome flat band depends on the complex interplay between
strong Coulomb repulsion, $3d$-orbital degeneracy, and flat band filling
fraction at different temperatures.