  Halide perovskites belong to an important family of semiconducting materials
with unique electronic properties that enable a myriad of applications,
especially in photovoltaics and optoelectronics. Their optical properties,
including photoluminescence quantum yield, are affected and notably enhanced at
crystal imperfections where the symmetry is broken and the density of states
increases. These lattice distortions can be introduced through structural phase
transitions, allowing charge gradients to appear near the interfaces between
phase structures. In this work, we demonstrate controlled multi-phase
structuring in a single perovskite crystal. The concept uses cesium lead
bromine (CsPbBr3) placed on a thermoplasmonic TiN/Si metasurface and enables
single, double and triple phase structures to form on demand above the room
temperature. This approach opens up application horizons of dynamically
controlled heterostructures with distinctive electronic and enhanced optical
properties.
