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Spontaneous emergence of Josephson junctions in homogeneous rings of single-crystal Sr2RuO4

The chiral p-wave order parameter in Sr$_\mathsf{2}$RuO$_\mathsf{4}$ would make it a special case amongst the unconventional superconductors. A consequence of this symmetry is the possible existence of superconducting domains of opposite chirality. At the boundary of such domains, the locally supressed condensate can produce an intrinsic Josephson junction. Here, we provide evidence of such junctions using mesoscopic rings, structured from Sr$_\mathsf{2}$RuO$_\mathsf{4}$ single crystals. Our order parameter simulations predict such rings to host stable domain walls across their arms. Thisis verified with transport experiments on loops, with a sharp transition at 1.5 K, which show distinct critical current oscillations with periodicity corresponding to the flux quantum. In contrast, loops with broadened transitions at around 3 K are void of such junctions and show standard Little-Parks oscillations. Our analysis demonstrates the junctions are of intrinsic origin and makes a compelling case for the existence of superconducting domains.