We construct and study a t-structure on p-typical cyclotomic spectra and explain how to recover crystalline cohomology of smooth schemes over perfect fields using this t-structure. Our main tool is a new approach to p-typical cyclotomic spectra via objects we call p-typical topological Cartier modules. Using these, we prove that the heart of the cyclotomic t-structure is the full subcategory of derived V -complete objects in the abelian category of p-typical Cartier modules.We say that a p-typicalThe existence and uniqueness of such a t-structure is a formal consequence of the fact that (CycSp p ) 0 is presentable and is closed under colimits and extensions in CycSp p . The difficult part of the theorem is the identification of the heart.Recall Bökstedt's theorem, which says that π * THH(F p ) = F p [b], a polynomial ring on a degree 2 generator. More generally, using the vanishing of the cotangent complex, one deduces that π * THH(k) = k[b] for any perfect ring k. Our interest in the cyclotomic t-structure was piqued by the discovery of the next result. 1 Unless otherwise specified, all quotients M/V n are computed in the derived sense (and hence are given as the cofiber of M V n −− → M in the derived category) as are all limits.Corollary 10. If X is a bounded below p-typical cyclotomic spectrum, then the natural S 1 -equivariant map TR(X) → X induces a p-adic equivalence TR(X) tS 1 → X tS 1 .Proof. By Theorem 9, the counit map TR(X)/TR(X) hCp → X is an equivalence. In particular, we have a cofiber sequence TR(X) hCp → TR(X) → X.Applying (−) tS 1 , we obtain a cofiber sequence p-adically equivalent to[NS17, Lemma II.4.2]. But, (TR(X) hCp ) tCp ≃ 0 by the Tate orbit lemma [NS17, Lemma I.2.1].2 In early talks on this project, we called these topological Dieudonné modules.
The cyclotomic t-structureIn this section we define the cyclotomic t-structure for integral and p-typical cyclotomic spectra in their genuine and non-genuine flavors. With some difficulty, one can prove some basic facts about truncations in