Optical phase change materials (O-PCMs) are a unique group of materials that feature drastic optical property changes upon solid-state phase transitions.¹ They have been widely adopted in photonic switches,^2–4 reconfigurable metasurfaces,^5–7 energy-efficient displays,⁸ and optical memory.⁹

However, current material choices, such as Ge-Sb-Te (GST), exhibit large contrasts of both refractive index (Δn) and optical loss (Δk) simultaneously. The coupling of both optical properties limits the function, performance, and scalability of many potential photonic applications.

In this research, we report on a new class of O-PCMs that breaks this traditional coupling—Ge-Sb-Se-Te (GSST).