Peculiar properties of Cr$_3$As$_3$-chain-based superconductors

TL;DR

This paper reviews the discovery, structure, electronic properties, and recent experimental progress of the novel quasi-one-dimensional Cr$_3$As$_3$-based superconductors, highlighting their unconventional superconductivity and open research questions.

Contribution

It provides a comprehensive overview of the structural, electronic, and physical properties of $A_2$Cr$_3$As$_3$ superconductors, including new experimental insights and discussion of open questions.

Findings

Structural characterization of Cr$_3$As$_3$ chains.

Evidence of unconventional superconductivity.

Recent experimental progress on physical properties.

Abstract

$A_2$Cr$_3$As$_3$ ($A$ = K, Rb, Cs) are the unique Cr-based ambient-pressure superconductors to date discovered by serendipity in 2015. The new superconducting family are structurally characterized by quasi one-dimensional [(Cr$_3$As$_3$)$^{2-}$]$_{\infty}$ double-walled subnanotubes, which exhibit peculiar properties that mostly point to unconventional superconductivity. In this conference paper, we first describe how the superconductors were discovered. Then we overview the recent progresses on crystal structure, electronic structures, theoretical models, and various physical properties in $A_2$Cr$_3$As$_3$. Some new experimental results are included. Finally we conclude by addressing the related open questions in this emerging subfield of superconductivity.