Superconductivity in kagome metals due to soft loop-current fluctuations

TL;DR

This paper proposes that soft loop-current fluctuations in kagome metals induce unconventional superconductivity, explaining multiple phases under pressure through multi-orbital interactions and collective modes.

Contribution

It introduces a mechanism involving loop-current fluctuations that accounts for different superconducting states in kagome metals, emphasizing multi-orbital effects and pressure-induced transitions.

Findings

Loop-current fluctuations generate low-energy collective modes.

Two distinct pairing channels: chiral d+id and s± states.

Pressure induces a Lifshitz transition stabilizing different superconducting states.

Abstract

We demonstrate that soft fluctuations of translation symmetry-breaking loop currents provide a mechanism for unconventional superconductivity in kagome metals that naturally addresses the multiple superconducting phases observed under pressure. Focusing on the rich multi-orbital character of these systems, we show that loop currents involving both vanadium and antimony orbitals generate low-energy collective modes that couple efficiently to electrons near the Fermi surface and mediate attractive interactions in two distinct unconventional pairing channels. While loop-current fluctuations confined to vanadium orbitals favor chiral $d+id$ superconductivity, which spontaneously breaks time-reversal symmetry, the inclusion of antimony orbitals stabilizes an $s^{\pm}$ state that is robust against disorder. We argue that these two states are realized experimentally as pressure increases and the antimony-dominated Fermi surface sheet undergoes a Lifshitz transition.