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2024 | Book

General Introduction Read chapter Read first chapter

Two-Dimensional Superconductivity in Rare Earth Oxybismuthides with Unusual Valent Bismuth Square Net

Author: Ryosuke Sei

Publisher: Springer Nature Singapore

Book Series : Springer Theses

Part of: Springer Professional "Wirtschaft+Technik" , Springer Professional "Technik"

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About this book

This book elucidates fascinating electronic phenomena of unusual Bi2-square net in layered R2O2Bi (R: rare earth) compounds using two approaches: the fabrication of epitaxial thin films and the synthesis of bulk polycrystalline powders. The Bi2-square net compounds are a promising platform to explore exotic physical properties originating from the interplay between a two-dimensional electronic state and strong spin–orbit coupling; however, there are few reports on Bi2-square net compounds due to the instability of unusual electronic configurations.

The book presents the development of synthetic routes for R2O2Bi compounds, such as novel solid phase epitaxy techniques and chemical control of crystal structure, demonstrating the intrinsic physical properties of Bi2-square net for the first time. The most notable finding is the successful induction of two-dimensional superconductivity in Bi2-square net with the coexistence of rich electronic phases. The book also discusses the superconducting mechanisms and the effect of R cation substitution in detail and describes the mechanical properties of Bi2-square net. These findings overturn the results of previous studies of R2O2Bi. The book sheds light on hidden layered compounds, representing a significant advance in the field.

Table of Contents

Frontmatter
Chapter 1. General Introduction
Abstract
Layered compounds are an intriguing group of compounds that exhibit novel superconducting phenomena such as high-temperature superconductivity and triplet superconductivity. This thesis provides detailed information about the newly discovered superconductor \({\textit{R}_{2}\text {O}_{2}\text {Bi}}\) (R: rare earth) with unusual \({\text {Bi}^{2-}}\) square net, including its specific properties and the mechanism of superconductivity. Layered compounds with Bi\(^{-}\) square net have been extensively studied until today, leading to the emergence of the wide variety of quantum phenomena such as anisotropic Dirac fermion and Kondo lattice behavior, while superconducting Bi\(^{-}\) square net has not been realized yet. In contrast to the rich material group of Bi\(^{-}\) square net compounds, there are few reports about the synthesis of \({\text {Bi}^{2-}}\) square net compounds except for \({\textit{R}_{2}\text {O}_{2}\text {Bi}}\) in polycrystalline form. Chapter [1] serves as an introduction, discussing an overview of layered superconductors and properties of layered compounds with Bi\(^{-}\) square net.
Ryosuke Sei
Chapter 2. Experimental Techniques
Abstract
In this chapter, an overview of the methods used for sample preparation and characterization of properties, as well as the underlying theories, is provided.
Ryosuke Sei
Chapter 3. Development of Solid-Phase Epitaxy Techniques
Abstract
This Chapter presents the first report on the epitaxial thin film growth of \({\textit{R}_{2}\text {O}_{2}\text {Bi}}\) using two newly developed solid-phase epitaxy techniques. The growth of epitaxial thin films of \({\textit{R}_{2}\text {O}_{2}\text {Bi}}\) poses a significant challenge due to the high vapor pressure and highly reductive state of \({\text {Bi}^{2{-}}}\). To address these challenges, I have devised methods involving the direct reaction of metal powders and thin films under reductive conditions, as well as the reaction of metal multilayers through post-annealing. Upon the evaluation of the properties of the resulting thin films, it has become apparent that they exhibit a strong spin-orbit coupling within a two-dimensional electronic state.
Ryosuke Sei
Chapter 4. Two-Dimensional Superconductivity in Polycrystalline
Abstract
This chapter presents a report on the discovery of two-dimensional superconductivity in the \({\text {Bi}^{2{-}}}\) square net within polycrystalline \({\text {Y}_{2}\text {O}_{2}\text {Bi}}\). Pristine \({\text {Y}_{2}\text {O}_{2}\text {Bi}}\) had previously been classified as non-superconducting in previous reports. However, a notable contrast emerged as superconductivity at approximately 2 K was induced by increasing the inter-net distance of \({\text {Bi}^{2{-}}}\) through the excessive incorporation of O into a hidden interstitial site. The bulk superconducting nature was evidenced through the observation of the Meissner effect and specific heat measurements. The emergence of superconductivity occurred by enhancing the distance between conductive inter-layers, without the need for carrier doping, which was scarcely observed in other superconductors. This suggests an unconventional superconducting mechanism. These concepts would be a novel route to induce superconductivity in layered compounds, shedding light on hidden superconducting compounds.
Ryosuke Sei
Chapter 5. Unusual Superconductivity in 
Abstract
This chapter introduces the detailed physical properties of polycrystalline \({\text {Tb}_{2}\text {O}_{2}\text {Bi}}\). Pristine \({\text {Tb}_{2}\text {O}_{2}\text {Bi}}\) exhibited a unique electronic phase, attributed to the charge density wave (CDW) transition of the \({\text {Bi}^{2{-}}}\) square net and the antiferromagnetic ordering of \({{\text {Tb}}^{3+}}\) connecting to giant magnetoresistance. These phenomena were absent in other \({\textit{R}_{2}\text {O}_{2}\text {Bi}}\) compounds. Electronic properties of \({\text {Tb}_{2}\text {O}_{2}\text {Bi}}\) were controllable through uniaxial chemical pressure along the c-axis. Substituting F for an O site resulted in c-axis shrinkage, suppressing the CDW transition but without inducing superconductivity. Conversely, the c-axis expansion via O incorporation induced the superconductivity with similar T \(_\text {c}\)trend to \({\text {Y}_{2}\text {O}_{2}\text {Bi}}\), and also correlated with the CDW transition suppression. The array of rich electronic phases suggests an unconventional superconducting behavior within the \({\text {Bi}^{2{-}}}\) square net of \({\text {Tb}_{2}\text {O}_{2}\text {Bi}}\).
Ryosuke Sei
Chapter 6. Universal Superconductivity in 
Abstract
This chapter summarizes the superconducting properties of \({\textit{R}_{2}\text {O}_{2}\text {Bi}}\) (R: Y, Tb, Dy, and Lu) compounds. In all compounds, O was incorporated into their frameworks, leading to the emergence of superconductivity under a universal rule: the enlargement of c/a, where T \(_\text {c}\) was a function of c/a irrespective of \({\textit{R}^{3+}}\). The threshold value was around 3.42. Rich electronic phases were observed depending on R in \({\textit{R}_{2}\text {O}_{2}\text {Bi}}\), suggesting that \({\textit{R}_{2}\text {O}_{2}\text {Bi}}\) provides an intriguing platform to investigate novel two-dimensional superconductivity.
Ryosuke Sei
Chapter 7. General Conclusion
Abstract
This chapter presents the general conclusion of this thesis.
Ryosuke Sei
Backmatter
Metadata
Title
Two-Dimensional Superconductivity in Rare Earth Oxybismuthides with Unusual Valent Bismuth Square Net
Author
Ryosuke Sei
Copyright Year
2024
Publisher
Springer Nature Singapore
Electronic ISBN
978-981-9973-13-2
Print ISBN
978-981-9973-12-5
DOI
https://doi.org/10.1007/978-981-99-7313-2

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