Suppression of spectral gap and flat bands on a cuprate superconductor side-surface.

Spectral gap and zero-energy flat bands are suppressed on the (110) side surface of overdoped La2−xSrxCuO4, despite theoretical expectations of their presence.

• Why it matters: Understanding surface states in cuprate superconductors is crucial because they influence superconducting properties and potential topological phenomena, yet they remain experimentally elusive due to cleaving challenges.
• What they did: Using focused-ion-beam milling, researchers prepared pristine (110) surfaces suitable for angle-resolved photoemission, and performed measurements with ~4 meV energy resolution to investigate spectral features.
• The result: The study found no evidence of a superconducting gap or flat-band peaks, with disorder modeled as Anderson-type broadening explaining the suppression, highlighting disorder's role in obscuring surface states.