Unusual Superconductivity in  \(\text {Tb}_{2}\text {O}_2\text {Bi}\)

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 \({\text {Tb}_{2}\text {O}_{2}\text {Bi}}\) .