Jochen Bruning, Pavel Exner, Vladimir A. Geyler
gaps in point-coupled periodic systems of manifolds
Irregular Spectral Asymptotics (2007)
The resolvent trace expansion for elliptic operators is a well established tool with many important applications in Geometric Analysis, see e.g. [Gi] and its bibliography. It is known for a long time...
On the spectrum of periodic elliptic operators (1992)
Jochen Bruning, Toshikazu Sunada
It was observed in [Su5] that the spectrum of a periodic Schrodinger operator