Symmetry Breaking and Ascending in the Magnetic Kagome Metal FeGe

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dc.citation.articleNumber011043en_US
dc.citation.issueNumber1en_US
dc.citation.journalTitlePhysical Review Xen_US
dc.citation.volumeNumber14en_US
dc.contributor.authorWu, Shangfeien_US
dc.contributor.authorKlemm, Mason L.en_US
dc.contributor.authorShah, Jayen_US
dc.contributor.authorRitz, Ethan T.en_US
dc.contributor.authorDuan, Chunruoen_US
dc.contributor.authorTeng, Xiaokunen_US
dc.contributor.authorGao, Binen_US
dc.contributor.authorYe, Fengen_US
dc.contributor.authorMatsuda, Masaakien_US
dc.contributor.authorLi, Fankangen_US
dc.contributor.authorXu, Xianghanen_US
dc.contributor.authorYi, Mingen_US
dc.contributor.authorBirol, Turanen_US
dc.contributor.authorDai, Pengchengen_US
dc.contributor.authorBlumberg, Girshen_US
dc.date.accessioned2024-07-25T20:56:27Zen_US
dc.date.available2024-07-25T20:56:27Zen_US
dc.date.issued2024en_US
dc.description.abstractSpontaneous symmetry breaking—the phenomenon in which an infinitesimal perturbation can cause the system to break the underlying symmetry—is a cornerstone concept in the understanding of interacting solid-state systems. In a typical series of temperature-driven phase transitions, higher-temperature phases are more symmetric due to the stabilizing effect of entropy that becomes dominant as the temperature is increased. However, the opposite is rare but possible when there are multiple degrees of freedom in the system. Here, we present such an example of a symmetry-ascending phenomenon upon cooling in a magnetic kagome metal FeGe by utilizing neutron Larmor diffraction and Raman spectroscopy. FeGe has a kagome lattice structure with simple A-type antiferromagnetic order below Néel temperature TN≈400 K and a charge density wave (CDW) transition at TCDW≈110 K, followed by a spin-canting transition at around 60 K. In the paramagnetic state at 460 K, we confirm that the crystal structure is indeed a hexagonal kagome lattice. On cooling to around TN, the crystal structure changes from hexagonal to monoclinic with in-plane lattice distortions on the order of 10−4 and the associated splitting of the double-degenerate phonon mode of the pristine kagome lattice. Upon further cooling to TCDW, the kagome lattice shows a small negative thermal expansion, and the crystal structure gradually becomes more symmetric upon further cooling. A tendency of increasing the crystalline symmetry upon cooling is unusual; it originates from an extremely weak structural instability that coexists and competes with the CDW and magnetic orders. These observations are against the expectations for a simple model with a single order parameter and hence can only be explained by a Landau free energy expansion that takes into account multiple lattice, charge, and spin degrees of freedom. Thus, the determination of the crystalline lattice symmetry as well as the unusual spin-lattice coupling is a first step towards understanding the rich electronic and magnetic properties of the system, and it sheds new light on intertwined orders where the lattice degree of freedom is no longer dominant.en_US
dc.identifier.citationWu, S., Klemm, M. L., Shah, J., Ritz, E. T., Duan, C., Teng, X., Gao, B., Ye, F., Matsuda, M., Li, F., Xu, X., Yi, M., Birol, T., Dai, P., & Blumberg, G. (2024). Symmetry Breaking and Ascending in the Magnetic Kagome Metal FeGe. Physical Review X, 14(1), 011043. https://doi.org/10.1103/PhysRevX.14.011043en_US
dc.identifier.digitalPhysRevX14011043en_US
dc.identifier.doihttps://doi.org/10.1103/PhysRevX.14.011043en_US
dc.identifier.urihttps://hdl.handle.net/1911/117537en_US
dc.language.isoengen_US
dc.publisherAmerican Physical Societyen_US
dc.rightsExcept where otherwise noted, this work is licensed under a Creative Commons Attribution (CC BY) license.  Permission to reuse, publish, or reproduce the work beyond the terms of the license or beyond the bounds of fair use or other exemptions to copyright law must be obtained from the copyright holder.en_US
dc.rights.urihttps://creativecommons.org/licenses/by/4.0/en_US
dc.titleSymmetry Breaking and Ascending in the Magnetic Kagome Metal FeGeen_US
dc.typeJournal articleen_US
dc.type.dcmiTexten_US
dc.type.publicationpublisher versionen_US
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