Evidence for an effective gauge field in flakes of superconducting 4Hb-TaS2

Abstract

Understanding the normal state of unconventional superconductors is central to uncovering the origin of superconductivity itself. Unconventional superconductivity often emerges from correlated electronic states characterized by intertwined symmetry-breaking orders. A striking example is 4Hb-TaS2, whose superconducting state exhibits a remarkable range of phenomena, including an unusual magnetic memory effect. Previous experiments showed that magnetic memory can be encoded above Tc and later revealed through spontaneous vortices below Tc, suggesting time-reversal symmetry breaking. However, since memory and vorticity are intertwined, this prevents establishing whether the effect results from trapped flux, weak conventional magnetism, or a true hidden electronic order. Here, we show that magnetic memory persists in the vortex-free Meissner regime of exfoliated 4Hb-TaS2 flakes, where it appears as a stable remanent modification of the superconducting screening response. Our results rule out explanations based on trapped vortices. Furthermore, the spatial profile of the flux generated by trained samples at zero field is inconsistent with conventional weak magnetism, suggesting a hidden electronic phase that imprints an effective flux on the superconducting condensate.