Toroidal loop-current order in kagome AV₃Sb₅: zero-field diode and anomalous Hall

Area of Science:

• Condensed Matter Physics
• Materials Science
• Superconductivity

Background:

• Kagome superconductors AV3Sb5 exhibit a complex interplay between charge density wave (CDW) order and exotic superconducting phenomena.
• Puzzling observations include the coexistence of a CDW-driven anomalous Hall effect (AHE) and a zero-field superconducting diode effect (SDE).

Purpose of the Study:

• To propose a unified theoretical mechanism explaining the coexisting AHE and SDE in AV3Sb5.
• To provide a framework for understanding the role of CDW order and emergent gauge fields in these phenomena.

Main Methods:

• Development of a symmetry-based, gauge-covariant Ginzburg-Landau theory.
• Incorporation of a composite toroidal loop-current order arising from triple-Q CDW.
• Modeling the coupling of the superconducting condensate to electromagnetic and emergent orbital gauge potentials.

Main Results:

• The theory predicts an emergent orbital gauge field sourced by the CDW loop-current order.
• A finite pairing momentum, enforced by a Lifshitz invariant, naturally yields the zero-field SDE.
• A mixed orbital-electromagnetic response explains the CDW-onset AHE.

Conclusions:

• The proposed unified mechanism successfully accounts for the observed AHE and SDE in AV3Sb5.
• Quantitative relations derived from the theory show semi-quantitative agreement with experimental data.
• The framework is consistent with phenomena in AV3Sb5 and twisted trilayer graphene, suggesting broader applicability.