@inproceedings{pavel2007on,
title={On the dense point and absolutely continuous spectrum for Hamiltonians with concentric shells},
author={Pavel Exner, and Martin Fraas},
url={http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191020131403009296673},
booktitle={Letters in Mathematical Physics},
volume={82},
number={1},
pages={25-37},
year={2007},
}
Pavel Exner, and Martin Fraas. On the dense point and absolutely continuous spectrum for Hamiltonians with concentric shells. 2007. Vol. 82. In Letters in Mathematical Physics. pp.25-37. http://archive.ymsc.tsinghua.edu.cn/pacm_paperurl/20191020131403009296673.