Interlayer Charge-Transfer Ferroelectric Fluctuations as a Pairing Mechanism in van der Waals Superconductors

TL;DR

This paper proposes that interlayer charge-transfer fluctuations near ferroelectric quantum critical points can mediate unconventional superconductivity in van der Waals materials, leading to novel pairing mechanisms and chiral states.

Contribution

It introduces a theory where interlayer charge transfer modes induce pairing, highlighting ferroelectric fluctuations as a new route to unconventional superconductivity in vdW systems.

Findings

Charge transfer modes can generate significant pairing interactions.

Proximity to ferroelectric quantum critical points enhances pairing strength.

Stability of chiral $s+i s$ superconducting states through Josephson coupling.

Abstract

Signatures of unconventional superconductivity have been reported in a wide range of van der Waals (vdW) materials. However, their microscopic origin remains unclear due to competing electronic orders, strong spin-orbit coupling, and structural instabilities in the normal state. Here we investigate the role of interlayer breathing and shear modes in superconducting vdW heterostructures. Contrary to conventional wisdom -- which assumes that weak interlayer bonding and large layer separation suppress electronic coupling to these modes -- we show that the associated charge transfer can generate a substantial pairing interaction. We develop a theory of superconductivity mediated by such interlayer modes and demonstrate that proximity to a ferroelectric or antiferroelectric quantum critical point provides a strong-coupling pairing channel. Within a two-dimensional model with SU(2) symmetry and in-plane isotropy, we find an accidental degeneracy between interlayer triplet states, which can occur even for an $s$-wave in-plane gap. We further show that Josephson coupling between layers, arising from either static magnetism or induced by paramagnetic correlations, can stabilize a time-reversal-symmetry-breaking superconducting state of the $s+i\,s$ type, which couples to magnetization when at least two mirror symmetries are absent. Our results are directly applicable to candidate chiral vdW superconductors such as 4Hb-TaS$_2$ and to sliding ferroelectric metals, exemplified by bilayer MoTe$_2$. More broadly, our work identifies ferroelectric fluctuations as a promising route to unconventional pairing in vdW systems and motivates experimental searches for chiral multicomponent superconductivity.