{"title":"I -centered versus F -centered orthorhombic symmetry and negative thermal expansion of the charge density wave of EuAl2Ga2","authors":"Harshit Agarwal, Surya Rohith Kotla, Leila Noohinejad, Biplab Bag, Claudio Eisele, Sitaram Ramakrishnan, Martin Tolkiehn, Carsten Paulmann, Arumugam Thamizhavel, Srinivasan Ramakrishnan, Sander van Smaalen","doi":"10.1103/physrevb.111.155144","DOIUrl":null,"url":null,"abstract":"Together with EuGa</a:mi>4</a:mn></a:msub></a:math> and <b:math xmlns:b=\"http://www.w3.org/1998/Math/MathML\"><b:msub><b:mi>EuAl</b:mi><b:mn>4</b:mn></b:msub><b:mo>,</b:mo><b:mo> </b:mo><b:mrow><b:msub><b:mi>EuAl</b:mi><b:mn>2</b:mn></b:msub><b:msub><b:mi>Ga</b:mi><b:mn>2</b:mn></b:msub></b:mrow></b:math> belongs to the <c:math xmlns:c=\"http://www.w3.org/1998/Math/MathML\"><c:msub><c:mi>BaAl</c:mi><c:mn>4</c:mn></c:msub></c:math> structure type with space group <d:math xmlns:d=\"http://www.w3.org/1998/Math/MathML\"><d:mrow><d:mi>I</d:mi><d:mn>4</d:mn></d:mrow></d:math>/. <e:math xmlns:e=\"http://www.w3.org/1998/Math/MathML\"><e:mrow><e:msub><e:mi>EuAl</e:mi><e:mn>2</e:mn></e:msub><e:msub><e:mi>Ga</e:mi><e:mn>2</e:mn></e:msub></e:mrow></e:math> develops an incommensurate charge density wave (CDW) at temperatures below <f:math xmlns:f=\"http://www.w3.org/1998/Math/MathML\"><f:mrow><f:msub><f:mi>T</f:mi><f:mi>CDW</f:mi></f:msub><f:mo>=</f:mo><f:mn>51</f:mn><f:mspace width=\"0.16em\"/><f:mi mathvariant=\"normal\">K</f:mi></f:mrow></f:math>. On the basis of temperature-dependent single-crystal x-ray diffraction data, the incommensurately modulated CDW crystal structure of <i:math xmlns:i=\"http://www.w3.org/1998/Math/MathML\"><i:mrow><i:msub><i:mi>EuAl</i:mi><i:mn>2</i:mn></i:msub><i:msub><i:mi>Ga</i:mi><i:mn>2</i:mn></i:msub></i:mrow></i:math> is determined to possess orthorhombic symmetry (0000)<j:math xmlns:j=\"http://www.w3.org/1998/Math/MathML\"><j:mrow><j:mi>s</j:mi><j:mn>0000</j:mn></j:mrow></j:math>. This symmetry is different from the orthorhombic -based symmetry of the CDW state of <k:math xmlns:k=\"http://www.w3.org/1998/Math/MathML\"><k:msub><k:mi>EuAl</k:mi><k:mn>4</k:mn></k:msub></k:math>. Nevertheless, both symmetries, (00)<l:math xmlns:l=\"http://www.w3.org/1998/Math/MathML\"><l:mrow><l:mi>s</l:mi><l:mn>00</l:mn></l:mrow></l:math> and (00)<m:math xmlns:m=\"http://www.w3.org/1998/Math/MathML\"><m:mrow><m:mi>s</m:mi><m:mn>00</m:mn></m:mrow></m:math>, lead to the same conclusion, that the CDW is supported by the layers of Al1 type atoms, while the Eu and Al2 or Ga atoms are not directly involved in CDW formation. The different symmetries of the CDW states of <n:math xmlns:n=\"http://www.w3.org/1998/Math/MathML\"><n:msub><n:mi>EuAl</n:mi><n:mn>4</n:mn></n:msub></n:math> and <o:math xmlns:o=\"http://www.w3.org/1998/Math/MathML\"><o:mrow><o:msub><o:mi>EuAl</o:mi><o:mn>2</o:mn></o:msub><o:msub><o:mi>Ga</o:mi><o:mn>2</o:mn></o:msub></o:mrow></o:math>, as well as the observation of negative thermal expansion in the CDW state of <p:math xmlns:p=\"http://www.w3.org/1998/Math/MathML\"><p:mrow><p:msub><p:mi>EuAl</p:mi><p:mn>2</p:mn></p:msub><p:msub><p:mi>Ga</p:mi><p:mn>2</p:mn></p:msub></p:mrow></p:math>, might be explained by the effects of Ga substitution in the latter compound. <jats:supplementary-material> <jats:copyright-statement>Published by the American Physical Society</jats:copyright-statement> <jats:copyright-year>2025</jats:copyright-year> </jats:permissions> </jats:supplementary-material>","PeriodicalId":20082,"journal":{"name":"Physical Review B","volume":"74 1","pages":""},"PeriodicalIF":3.7000,"publicationDate":"2025-04-24","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":null,"platform":"Semanticscholar","paperid":null,"PeriodicalName":"Physical Review B","FirstCategoryId":"101","ListUrlMain":"https://doi.org/10.1103/physrevb.111.155144","RegionNum":2,"RegionCategory":"物理与天体物理","ArticlePicture":[],"TitleCN":null,"AbstractTextCN":null,"PMCID":null,"EPubDate":"","PubModel":"","JCR":"Q1","JCRName":"Physics and Astronomy","Score":null,"Total":0}
引用次数: 0
Abstract
Together with EuGa4 and EuAl4,EuAl2Ga2 belongs to the BaAl4 structure type with space group I4/. EuAl2Ga2 develops an incommensurate charge density wave (CDW) at temperatures below TCDW=51K. On the basis of temperature-dependent single-crystal x-ray diffraction data, the incommensurately modulated CDW crystal structure of EuAl2Ga2 is determined to possess orthorhombic symmetry (0000)s0000. This symmetry is different from the orthorhombic -based symmetry of the CDW state of EuAl4. Nevertheless, both symmetries, (00)s00 and (00)s00, lead to the same conclusion, that the CDW is supported by the layers of Al1 type atoms, while the Eu and Al2 or Ga atoms are not directly involved in CDW formation. The different symmetries of the CDW states of EuAl4 and EuAl2Ga2, as well as the observation of negative thermal expansion in the CDW state of EuAl2Ga2, might be explained by the effects of Ga substitution in the latter compound. Published by the American Physical Society2025
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Physical Review B (PRB) is the world’s largest dedicated physics journal, publishing approximately 100 new, high-quality papers each week. The most highly cited journal in condensed matter physics, PRB provides outstanding depth and breadth of coverage, combined with unrivaled context and background for ongoing research by scientists worldwide.
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