Researchers used a single-spin quantum sensor to directly image special electronic states that live at the edges of a twisted cuprate superconductor. The material is Bi2Sr2CaCu2O8+x (BSCCO), a high-temperature superconductor made into a two-layer stack with a precise twist between the layers. Theory predicts that a 45° twist can open a small topological gap in the bulk and force the system to host chiral edge modes — edge-only channels that carry quasiparticle excitations. The team reports scanning-probe measurements that reveal these edge modes in real space.

To make the images, the authors built twisted BSCCO devices using a cryogenic, solvent-free stacking method with twist-angle control to about ±0.1°. The top and bottom flakes were roughly 10 nm and 30 nm thick. They scanned a nitrogen‑vacancy (NV) center — a single quantum spin implanted at the tip of a diamond nanopillar — about 60 nm above the sample. The NV spin is sensitive to tiny, high-frequency magnetic fluctuations. The group first checked superconductivity in the devices with static NV magnetometry, observed Meissner screening below a superconducting transition near 86 K, and then moved to a dynamical sensing method.

The key sensing method is single-spin relaxometry. In plain terms, quasiparticles in the superconductor scatter and produce fluctuating magnetic fields at certain frequencies. When those fluctuations match the NV’s electron spin resonance (ESR) frequency, they drive the NV spin to relax faster. By scanning the NV across the sample and recording the NV relaxation rate, the authors found clear peaks of enhanced relaxation at physical sample edges. A direct comparison of relaxation spectra taken on and off an edge (reported at 50 K) showed accelerated NV spin decay above the edge, consistent with extra quasiparticle noise coming from edge channels. The measured relaxation also followed a distance dependence consistent with edge-localized noise.