Fine-grained topological structures hidden in the Fermi sea
The study addresses the limitation of using only Euler characteristic ($\chi_F$) to describe Fermi sea topology, which fails to capture fine-grained structures. The authors introduce a 'structural resolution factor' ($g$) to provide a complete topological description. This framework shows that superconducting phases inherit this fine structure from their metallic parents, leading to anomalous gapless boundary states at interfaces.