Superconductivity in titanium-based pnictide oxide compounds

TL;DR

This paper reviews the discovery and properties of titanium-based pnictide oxide superconductors, highlighting their layered structure, coexistence of density wave phases with superconductivity, and the open questions in understanding their mechanisms.

Contribution

It provides a comprehensive summary of experimental and theoretical findings on Ti-based pnictide oxides, emphasizing their unique features and unresolved issues.

Findings

Coexistence of superconductivity and density wave phases.

Metallic parent compounds with Fermi surface nesting.

Open questions on the nature of superconductivity and interactions.

Abstract

Superconductivity in a novel class of layered materials, Ti-based pnictide oxides, was recently discovered. These compounds have attracted interest since they combine features of copper oxide and iron pnictide superconductors. Here the transition metal (titanium) forms two-dimensional Ti$_2$O layers (anti structure to the CuO$_2$ planes), capped by pnictogen ions (similar to Fe$_2$As$_2$ layers). The pnictide oxide compounds show a spin or charge density wave phase which coexists with superconductivity in some members of the family. Unlike the cuprates, but similar to iron pnictides, the parent compounds of pnictide oxides are metals with specific nesting properties of the Fermi surface which leads to the density wave instability. The nature of the superconductivity, coexisting with the density wave order, and the possible competition or mutual interaction between both states is one of the central questions of recent studies. This short review summarizes the current knowledge from an experimental as well as theoretical point of view and discusses some of the open questions and possible future developments.