Anomalous narrow-band correlation in a natural superconducting heterostructure.

A flat band near the Fermi level was observed only on the surface layer of 4Hb-TaS2, challenging current theories of electronic correlation in this heterostructure.

• Why it matters: Understanding the electronic properties of layered heterostructures like 4Hb-TaS2 is crucial for explaining phenomena such as chiral and topological superconductivity, but current models rely on the assumption of a flat band in the bulk.
• What they did: Using angle-resolved photoemission spectroscopy, the study identified a flat band exclusively on the surface layer with broken translational symmetry, and revealed a pseudogap and anomalous doping effects there.
• The result: These findings question the role of the flat band in bulk layers and provide new insights into the coexistence of electronic orders, impacting theories of correlated phenomena in layered superconducting heterostructures.