Photo-induced optical activity in phase-change memory materials

We demonstrate that optical activity in amorphous isotropic thin films of pure Ge 2 Sb 2 Te 5 and N-doped Ge 2 Sb 2 Te 5 N phase-change memory materials can be induced using rapid photo crystallisation with circularly polarised laser light. The new anisotropic phase transition has been confirmed by circular dichroism measurements. This opens up the possibility of controlled induction of optical activity at the nanosecond time scale for exploitation in a new generation of high-density optical memory, fast chiroptical switches and chiral metamaterials.