Spin-orbit driven Peierls transition and possible exotic superconductivity in CsW$_{2}$O$_{6}$

TL;DR

This study reveals that CsW$_{2}$O$_{6}$ undergoes a 3D Peierls transition driven by spin-orbit coupling, and proposes the potential for exotic superconductivity in its high-temperature phase, which has not been observed before.

Contribution

The paper identifies the correct crystal structure of CsW$_{2}$O$_{6}$, characterizes its Peierls transition driven by spin-orbit interaction, and predicts a novel superconducting state in the high-temperature phase.

Findings

The low-temperature structure is larger than previously reported.

The insulating phase is a 3D Peierls transition, not Mott or dimer-singlet.

A potential $e_{g}+ie_{g}$ superconducting state could exist in the high-temperature phase.

Abstract

We study \textit{ab initio} a pyrochlore compound, CsW$_{2}$O$_{6}$, which exhibits a yet unexplained metal-insulator transition. We find that (1) the reported low-$T$ structure is likely inaccurate and the correct structure has a twice larger cell; (2) the insulating phase is not of a Mott or dimer-singlet nature, but a rare example of a 3D Peierls transition, with a simultaneous condensation of three density waves; (3) spin-orbit interaction plays a crucial role, forming well-nested bands. The high-$T$ (HT) phase, if stabilized, could harbor a unique $e_{g}+ie_{g}$ superconducting state that breaks the time reversal symmetry, but is not chiral. This state was predicted in 1999, but never observed. We speculate about possible ways to stabilize the HT phase while keeping the conditions for superconductivity.