“…To our best knowledge, most of the work on XFEM/GFEM is for source problems or interface source problems and there is no work on these methods for solving differential eigenvalue problems. Traditionally, differential eigenvalue problems are solved by using standard FEMs (c.f., [8,11,16,17,[36][37][38]42]), isogeometric analysis (c.f., [19,29,30]), discontinuous Galerkin methods (c.f., [4,26,27]), etc. We are not going to expand the literature review here and only mention the most-recent quadrature rule blending techniques developed in [3] for FEMs and in [13,15,20,21,39] for isogeometric analysis.…”