Cryogenic electron microscopy of intra-unit-cell charge order textures in a manganite*

Charge-ordered states involve a complex interplay between charge, spin, orbital and lattice degrees of freedom. The intra-unit-cell arrangement within charge order superlattices (site vs bond order) can lead to even richer physics by breaking additional symmetries and allowing novel couplings. Here we use atomic-resolution cryogenic scanning transmission electron microscopy (cryo-STEM) to visualize charge-ordered states in a half-doped manganite (Nd_1/2Sr_1/2MnO₃). In addition to observing that the system hosts site-centered charge ordering, we discover the nanoscale coexistence of an intermediate state which mixes site and bond orders. In agreement with theoretical proposals, we confirm that this intermediate state breaks inversion symmetry. Finally we show that nonlinear couplings of distinct lattice modes locally control the selection between these competing charge order states.