EuAl2Ga2电荷密度波的I中心与F中心正交对称及负热膨胀

IF 3.7 2区物理与天体物理 Q1 Physics and Astronomy

Physical Review B Pub Date : 2025-04-24 DOI:10.1103/physrevb.111.155144

Harshit Agarwal, Surya Rohith Kotla, Leila Noohinejad, Biplab Bag, Claudio Eisele, Sitaram Ramakrishnan, Martin Tolkiehn, Carsten Paulmann, Arumugam Thamizhavel, Srinivasan Ramakrishnan, Sander van Smaalen

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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. 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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. 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引用次数: 0

摘要

EuAl2Ga2与EuGa4和EuAl4同属于空间群为I4/的BaAl4结构类型。在温度低于TCDW=51K时，EuAl2Ga2会产生不相称的电荷密度波（CDW）。根据随温度变化的单晶 X 射线衍射数据，确定 EuAl2Ga2 的非同调 CDW 晶体结构具有正交对称性 (0000)s0000。这种对称性与 EuAl4 的 CDW 态的正交对称性不同。尽管如此，(00)s00 和 (00)s00 这两种对称性得出了相同的结论，即 CDW 由 Al1 型原子层支撑，而 Eu 和 Al2 或 Ga 原子并不直接参与 CDW 的形成。EuAl4和EuAl2Ga2的CDW态的不同对称性，以及在EuAl2Ga2的CDW态中观察到的负热膨胀，可能可以用后者化合物中Ga替代的影响来解释。由美国物理学会出版 2025

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I -centered versus F -centered orthorhombic symmetry and negative thermal expansion of the charge density wave of EuAl2Ga2

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 Society

2025

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来源期刊

Physical Review B 物理-物理：凝聚态物理

CiteScore

6.70

自引率

32.40%

发文量

审稿时长

3.0 months

期刊介绍： 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. PRB covers the full range of condensed matter, materials physics, and related subfields, including: -Structure and phase transitions -Ferroelectrics and multiferroics -Disordered systems and alloys -Magnetism -Superconductivity -Electronic structure, photonics, and metamaterials -Semiconductors and mesoscopic systems -Surfaces, nanoscience, and two-dimensional materials -Topological states of matter