It has long been known that the differential operator $D$ represents a typical examples of unbounded operators in many Banach spaces including the classical Fock spaces, the Fock--Sobolev spaces, and the generalized Fock spaces where the weight decays faster than the Gaussian weight. In this note we identify Fock type spaces where the operator admits some basic spectral structures including compactness and membership in the Schatten $\mathcal{S}_p$ classes. We also showed that its nontrivial spectrum while acting on such spaces is precisely the closed unit disk $\D$ in the complex plane. 查看全文>>