Quantum interference in a twisted high-Tc SQUID senses emergent interfacial order

Engineering artificial systems by twisting van der Waals materials provides an excellent platform for exploring emergent quantum phenomena. Recent advances in fabrication enable studies of interfacial superconductivity in twisted cuprates. In our work, we fabricate superconducting quantum interference devices (SQUID) that utilize the twisted interface of Bi2Sr2CaCu2O8+δ, a high-Tc cuprate superconductor. By measuring the magnetic field modulation of differential resistance, we find a π phase difference between the two Josephson junction arms of the SQUID reflecting chiral time-reversal symmetry-broken superconducting order – a crucial aspect inaccessible to single Josephson junction. Our observations also indicate co-tunneling of the Cooper pairs. Additionally, these SQUIDs are well-suited for use as state-of-the-art flux sensors near 77 K. Stabilizing superconducting orders using twisted interfaces and probing them via quantum interference opens avenues for understanding unconventional superconductors. Our architecture can probe charge transport and superconducting order symmetry at interfaces in other systems, demonstrating broad applicability beyond cuprates. The authors study superconducting quantum interference devices (SQUIDs) constructed from twisted thin flakes of the cuprate superconductor Bi2Sr2CaCu2O8+δ. They find a π phase difference between the two Josephson junction arms of the SQUID reflecting chiral superconducting order of opposite chirality in the two arms.