Connor A. Occhialini, Yi Tseng, Hebatalla Elnaggar, Qian Song, Mark Blei, Seth Ariel Tongay, Valentina Bisogni, Frank M. F. de Groot, Jonathan Pelliciari, Riccardo Comin
{"title":"二卤化镍电荷转移绝缘体中激子的性质及其配位体介导的脱ocalization","authors":"Connor A. Occhialini, Yi Tseng, Hebatalla Elnaggar, Qian Song, Mark Blei, Seth Ariel Tongay, Valentina Bisogni, Frank M. F. de Groot, Jonathan Pelliciari, Riccardo Comin","doi":"10.1103/physrevx.14.031007","DOIUrl":null,"url":null,"abstract":"The fundamental optical excitations of correlated transition-metal compounds are typically identified with multielectronic transitions localized at the transition-metal site, such as <math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>d</mi><mi>d</mi></math> transitions. In this vein, intense interest has surrounded the appearance of sharp, below-band-gap optical transitions, i.e., excitons, within the magnetic phase of correlated <math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msup><mrow><mi>Ni</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow></math> van der Waals magnets. The interplay of magnetic and charge-transfer insulating ground states in <math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msup><mrow><mi>Ni</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow></math> systems raises intriguing questions on the roles of long-range magnetic order and of metal-ligand charge transfer in the exciton nature, which inspired microscopic descriptions beyond typical <math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>d</mi><mi>d</mi></math> excitations. Here we study the impact of charge transfer and magnetic order on the excitation spectrum of the nickel dihalides (<math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>Ni</mi><msub><mrow><mi>X</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math>, <math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><mi>X</mi><mo>=</mo><mi>Cl</mi></mrow></math>, Br, and I) using Ni-<math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><msub><mi>L</mi><mn>3</mn></msub></math> edge resonant inelastic x-ray scattering (RIXS). In all compounds, we detect sharp excitations, analogous to the recently reported excitons, and assign them to spin-singlet multiplets of octahedrally coordinated <math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><mrow><msup><mrow><mi>Ni</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow></math> stabilized by intra-atomic Hund’s exchange. Additionally, we demonstrate that these excitons are dispersive using momentum-resolved RIXS. Our data evidence a ligand-mediated multiplet dispersion, which is tuned by the charge-transfer gap and independent of the presence of long-range magnetic order. This reveals the mechanisms governing nonlocal interactions of on-site <math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>d</mi><mi>d</mi></math> excitations with the surrounding crystal or magnetic structure, in analogy to ground-state superexchange. These measurements thus establish the roles of magnetic order, self-doped ligand holes, and intersite-coupling mechanisms for the properties of <math display=\"inline\" xmlns=\"http://www.w3.org/1998/Math/MathML\"><mi>d</mi><mi>d</mi></math> excitations in charge-transfer insulators.","PeriodicalId":20161,"journal":{"name":"Physical Review X","volume":null,"pages":null},"PeriodicalIF":11.6000,"publicationDate":"2024-07-12","publicationTypes":"Journal Article","fieldsOfStudy":null,"isOpenAccess":false,"openAccessPdf":"","citationCount":"0","resultStr":"{\"title\":\"Nature of Excitons and Their Ligand-Mediated Delocalization in Nickel Dihalide Charge-Transfer Insulators\",\"authors\":\"Connor A. Occhialini, Yi Tseng, Hebatalla Elnaggar, Qian Song, Mark Blei, Seth Ariel Tongay, Valentina Bisogni, Frank M. F. de Groot, Jonathan Pelliciari, Riccardo Comin\",\"doi\":\"10.1103/physrevx.14.031007\",\"DOIUrl\":null,\"url\":null,\"abstract\":\"The fundamental optical excitations of correlated transition-metal compounds are typically identified with multielectronic transitions localized at the transition-metal site, such as <math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><mi>d</mi><mi>d</mi></math> transitions. In this vein, intense interest has surrounded the appearance of sharp, below-band-gap optical transitions, i.e., excitons, within the magnetic phase of correlated <math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><mrow><msup><mrow><mi>Ni</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow></math> van der Waals magnets. The interplay of magnetic and charge-transfer insulating ground states in <math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><mrow><msup><mrow><mi>Ni</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow></math> systems raises intriguing questions on the roles of long-range magnetic order and of metal-ligand charge transfer in the exciton nature, which inspired microscopic descriptions beyond typical <math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><mi>d</mi><mi>d</mi></math> excitations. Here we study the impact of charge transfer and magnetic order on the excitation spectrum of the nickel dihalides (<math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><mrow><mi>Ni</mi><msub><mrow><mi>X</mi></mrow><mrow><mn>2</mn></mrow></msub></mrow></math>, <math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><mrow><mi>X</mi><mo>=</mo><mi>Cl</mi></mrow></math>, Br, and I) using Ni-<math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><msub><mi>L</mi><mn>3</mn></msub></math> edge resonant inelastic x-ray scattering (RIXS). In all compounds, we detect sharp excitations, analogous to the recently reported excitons, and assign them to spin-singlet multiplets of octahedrally coordinated <math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><mrow><msup><mrow><mi>Ni</mi></mrow><mrow><mn>2</mn><mo>+</mo></mrow></msup></mrow></math> stabilized by intra-atomic Hund’s exchange. Additionally, we demonstrate that these excitons are dispersive using momentum-resolved RIXS. Our data evidence a ligand-mediated multiplet dispersion, which is tuned by the charge-transfer gap and independent of the presence of long-range magnetic order. This reveals the mechanisms governing nonlocal interactions of on-site <math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><mi>d</mi><mi>d</mi></math> excitations with the surrounding crystal or magnetic structure, in analogy to ground-state superexchange. These measurements thus establish the roles of magnetic order, self-doped ligand holes, and intersite-coupling mechanisms for the properties of <math display=\\\"inline\\\" xmlns=\\\"http://www.w3.org/1998/Math/MathML\\\"><mi>d</mi><mi>d</mi></math> excitations in charge-transfer insulators.\",\"PeriodicalId\":20161,\"journal\":{\"name\":\"Physical Review X\",\"volume\":null,\"pages\":null},\"PeriodicalIF\":11.6000,\"publicationDate\":\"2024-07-12\",\"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.14.031007\",\"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}","platform":"Semanticscholar","paperid":null,"PeriodicalName":"Physical Review X","FirstCategoryId":"101","ListUrlMain":"https://doi.org/10.1103/physrevx.14.031007","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}
Nature of Excitons and Their Ligand-Mediated Delocalization in Nickel Dihalide Charge-Transfer Insulators
The fundamental optical excitations of correlated transition-metal compounds are typically identified with multielectronic transitions localized at the transition-metal site, such as transitions. In this vein, intense interest has surrounded the appearance of sharp, below-band-gap optical transitions, i.e., excitons, within the magnetic phase of correlated van der Waals magnets. The interplay of magnetic and charge-transfer insulating ground states in systems raises intriguing questions on the roles of long-range magnetic order and of metal-ligand charge transfer in the exciton nature, which inspired microscopic descriptions beyond typical excitations. Here we study the impact of charge transfer and magnetic order on the excitation spectrum of the nickel dihalides (, , Br, and I) using Ni- edge resonant inelastic x-ray scattering (RIXS). In all compounds, we detect sharp excitations, analogous to the recently reported excitons, and assign them to spin-singlet multiplets of octahedrally coordinated stabilized by intra-atomic Hund’s exchange. Additionally, we demonstrate that these excitons are dispersive using momentum-resolved RIXS. Our data evidence a ligand-mediated multiplet dispersion, which is tuned by the charge-transfer gap and independent of the presence of long-range magnetic order. This reveals the mechanisms governing nonlocal interactions of on-site excitations with the surrounding crystal or magnetic structure, in analogy to ground-state superexchange. These measurements thus establish the roles of magnetic order, self-doped ligand holes, and intersite-coupling mechanisms for the properties of excitations in charge-transfer insulators.
期刊介绍:
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.