  Confined samples of liquid crystals are characterized by a variety of
topological defects and can be exposed to external constraints such as extreme
confinements with nontrivial topology. Here we explore the intrinsic structure
of smectic colloidal layers dictated by the interplay between entropy and an
imposed external topology. Considering an annular confinement as a basic
example, a plethora of competing states is found with nontrivial defect
structures ranging from laminar states to multiple smectic domains and arrays
of edge dislocations which we refer to as Shubnikov states in formal analogy to
the characteristic of type-II superconductors. Our particle-resolved results,
gained by a combination of real-space microscopy of thermal colloidal rods and
fundamental-measure-based density functional theory of hard anisotropic bodies,
agree on a quantitative level.
