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

TL;DR

This study demonstrates that twisted high-Tc cuprate interfaces can host emergent chiral and time-reversal symmetry-broken superconducting orders, revealed through quantum interference in SQUID devices, with implications for understanding unconventional superconductivity.

Contribution

The paper introduces a novel SQUID device utilizing a twisted cuprate interface, revealing emergent superconducting order and chiral phases not accessible in previous single-junction studies.

Findings

Observation of a $ ext{ extpi}$ phase difference indicating chiral order

Detection of co-tunneling of Cooper pairs

High flux noise sensitivity near 77 K

Abstract

Engineering artificial systems by twisting and stacking van der Waals materials has proven to be an excellent platform for exploring emergent quantum phenomena that can be significantly different from the constituents. Recent advances in the fabrication of high-quality twisted interfaces provide a unique opportunity to study the little-explored interfacial superconducting order in twisted cuprate superconductors. In our work, we fabricate superconducting quantum interference devices (SQUID) that utilize the twisted interface of $\mathrm{Bi_2Sr_2CaCu_2O_{8+\delta}}$, a high-Tc cuprate superconductor. By measuring the magnetic field modulation of switching current and differential resistance, we find a $\mathrm{\pi}$ phase difference between the two Josephson junction arms of the SQUID reflecting chiral superconducting order -- a crucial aspect inaccessible to single Josephson junction devices of the past. Our observations also indicate co-tunneling of the Cooper pairs and a time-reversal symmetry-broken emergent superconducting order. Additionally, these SQUIDs are well suited for use as state-of-the-art flux sensors close to 77 K, achieving a flux noise sensitivity of $\sim$1.5 $\mathrm{\mu\Phi_0/\sqrt{Hz}}$. Stabilizing new superconducting orders using twisted interfaces and probing them using quantum interference opens new avenues to understanding the microscopic origin of unconventional superconductors. Our SQUID architecture is suitable for investigating the charge transport mechanisms and the symmetry of superconducting order at the interfaces of other systems, reflecting the broad applicability beyond cuprate superconductors.