Massana-Cid, HelenaMeng, FanlongMatsunaga, DaikiGolestanian, RaminTierno, Pietro2019-10-282019-10-282019-06-042041-1723https://hdl.handle.net/2445/143299The process of crystallization is difficult to observe for transported, out-of-equilibrium sys-tems, as the continuous energy injection increases activity and competes with ordering. Inemergingfields such as microfluidics and active matter, the formation of long-range order isoften frustrated by the presence of hydrodynamics. Here we show that a population ofcolloidal rollers assembled by magneticfields into large-scale propelling carpets can formperfect crystalline materials upon suitable balance between magnetism and hydrodynamics.We demonstrate afield-tunable annealing protocol based on a controlled colloidalflow abovethe carpet that enables complete crystallization after a few seconds of propulsion. Thestructural transition from a disordered to a crystalline carpet phase is captured via spatial andtemporal correlation functions. Ourfindings unveil a novel pathway to magnetically annealclusters of propelling particles, bridging driven systems with crystallization and freezing inmaterial science.application/pdfengcc-by (c) Massana Cid, Helena et al., 2019http://creativecommons.org/licenses/by/3.0/esCol·loidesPropietats magnètiquesCristal·litzacióHidrodinàmicaColloidsMagnetic propertiesCrystallizationHydrodynamicsinfo:eu-repo/semantics/article6922302019-10-28info:eu-repo/semantics/openAccess31164640