Active solids, or self-propelling units elastically coupled on a lattice, are recently of growing interest and are predicted to show emerging out-of-equilibrium behaviour, while they can inspire the design of numerous applications. However, experimental studies have been few and limited due to the difficulty of practically realising systems of hundreds of confined active particles. The results of StaMACS show for the first time an experimental realisation of a large ordered active solid with activity and confinement tuneable in-situ and on- command. This two-dimensional active solid is composed of repulsive magnetic particles activated by a photokinetic bacterial bath. In this way, our crystal is in contact with two effective temperature reservoirs: 1) the thermal or magnetic temperature, related to the strength of the inter-particle repulsion and controlled by the magnetic field, and the active temperature, related to the power of the light-driven bacterial bath and controlled by green light. We tuned both independently and show that there is a regime in which these two temperatures are not equivalent. We drew an off-equilibrium phase diagram depending on the two temperatures of the system and discovered some unexpected differences between melting in the passive system and active melting. Furthermore, we studied this active system when the active temperature changes in space. The results of StaMACS provide a novel testbed for active solids with an unprecedented degree of tunability. By revealing new complex dynamics, the project expands the physics of active matter to the realm of non-equilibrium colloidal solids, bringing the field closer to the practical realization of new soft materials with distinctive properties and high tunability.
