Higgs-Leggett mechanism for the elusive $${\phi }_{0}/3={hc}/6e$$ oscillation in Little-Parks setup of Kagome superconductor CsV3Sb5

Abstract

A recent Little-Parks experiment in Kagome-structured superconductor CsV3Sb5 demonstrated resistance oscillations with period $${\phi }_{0}/3={hc}/6e$$ . Here, we perform analysis based on a theory involving three $$2{{{{{\rm{e}}}}}}$$ superconductivity (SC) order parameters associated with the three reciprocal lattice vectors which connect M points of the hexagonal Brillouin zone. In a ring geometry we find that, as a series of intermediate states, phase of one SC order parameter winds 2π more or less than the other two ones around the ring, which yields local free-energy minima at integer multiples of $${\phi }_{0}/3$$ . It is unveiled that the ground-state degeneracy associated with a Z2 chirality is crucial, and the Higgs-Leggett mechanism stabilizes domain walls (DWs) between chiral domains. At low temperatures DWs are expelled from the system resulting in free-energy minima only at integer multiples of $${\phi }_{0}$$ . Our theory explains successfully the fractional quantization of magnetic flux $${\phi }_{0}/3$$ observed in experiments, which opens a door for approaching rich physics of Kagome superconductors. Recent experiments on the Kagome superconductor (SC) CsV3Sb5 indicated 6e-charge flux quantization, which may impact our understanding of the electron pairing in SCs. The authors propose a multicomponent Landau-Ginzburg theory to explain the observed phenomenon, concluding that it is likely related to an exotic Higgs-Leggett collective mode involving three Cooper pairs in an intermediate phase.