Interfacial Oxygen-Driven Charge Localization and Plasmon Excitation in Unconventional Superconductors

Chi Sin Tang; Xinmao Yin; Shengwei Zeng; Jing Wu; Ming Yang; Ping Yang; Caozheng Diao; Yuan Ping Feng; Mark B H Breese; Elbert E M Chia; Thirumalai Venkatesan; Manish Chhowalla; Ariando Ariando; Andrivo Rusydi; Andrew T S Wee

doi:10.1002/adma.202000153

Interfacial Oxygen-Driven Charge Localization and Plasmon Excitation in Unconventional Superconductors

Adv Mater. 2020 Aug;32(34):e2000153. doi: 10.1002/adma.202000153. Epub 2020 Jul 9.

Authors

Chi Sin Tang^{1

2}, Xinmao Yin^{1

3}, Shengwei Zeng^{1

4}, Jing Wu⁵, Ming Yang⁵, Ping Yang³, Caozheng Diao³, Yuan Ping Feng¹, Mark B H Breese^{1

3}, Elbert E M Chia⁶, Thirumalai Venkatesan^{1

2

4

7}, Manish Chhowalla⁸, Ariando Ariando^{1

2

4}, Andrivo Rusydi^{1

2

3}, Andrew T S Wee^{1

2

3

9}

Affiliations

¹ Department of Physics, Faculty of Science, National University of Singapore, S12 Science Drive 3, Singapore, 117551, Singapore.
² NUS Graduate School for Integrative Sciences and Engineering, National University of Singapore, 21 Lower Kent Ridge, Singapore, 119077, Singapore.
³ Singapore Synchrotron Light Source, National University of Singapore, 5 Research Link, Singapore, 117603, Singapore.
⁴ NUSNNI-NanoCore, National University of Singapore, Singapore, 117411, Singapore.
⁵ Institute of Materials Research and Engineering, A∗STAR (Agency for Science, Technology and Research), 2 Fusionopolis Way, Singapore, 138634, Singapore.
⁶ Division of Physics and Applied Physics, School of Physical and Mathematical Sciences, Nanyang Technological University, Singapore, 637371, Singapore.
⁷ Department of Electrical and Computer Engineering, National University of Singapore, Singapore, 117583, Singapore.
⁸ Department of Materials Science & Metallurgy, University of Cambridge, Cambridge, CB3 0FS, UK.
⁹ Centre for Advanced 2D Materials and Graphene Research Centre, National University of Singapore, Singapore, 117546, Singapore.

PMID: 32643185
DOI: 10.1002/adma.202000153

Abstract

Charge localization is critical to the control of charge dynamics in systems such as perovskite solar cells, organic-, and nanostructure-based photovoltaics. However, the precise control of charge localization via electronic transport or defect engineering is challenging due to the complexity in reaction pathways and environmental factors. Here, charge localization in optimal-doped La_1.85 Sr_0.15 CuO₄ thin-film on SrTiO₃ substrate (LSCO/STO) is investigated, and also a high-energy plasmon is observed. Charge localization manifests as a near-infrared mid-gap state in LSCO/STO. This is ascribed to the interfacial hybridization between the Ti3d-orbitals of the substrate and O2p-orbitals of the film. The interfacial effect leads to significant changes in the many-body correlations and local-field effect. The local-field effect results in an inhomogeneous charge distribution, and due to perturbation by an external field, the high polarizability of this nonuniform charge system eventually generates the high-energy plasmon. Transformation of the electronic correlations in LSCO/STO is further demonstrated via temperature-dependent spectral-weight transfer. This study of charge localization in cuprates and interfacial hybridization provides important clues to their electronic structures and superconductive properties.

Keywords: charge localizations; interfacial excitons; orbital hybridizations; plasmons; unconventional superconductors.