Optoelectronic materials

Optoelectronic materials have found much use in memory devices, the context in which we study them. A particular class are so-called phase change materials, which have low electronic conductivity, low optical reflectivity and low density in the amorphous phase while being being denser, better reflecting and better conducting in the crystalline phase. Various competing theories exist suggesting explanations for the contrast of the behavior between crystalline and amorphous phase. Our view is that the local symmetry around certain ions determines the physical behavior at large scales. As such, our approach to the investigated materials class is the only one explaining why the compressibility of the amorphous alloys is twice as large as that of the crystalline phase. An interesting implication of our view is that it should be possible, in principle, to induce a phase switch between poor and good conductivity through piezoelectric actuators. Such a switch would be faster and less energy intensive than through melting and recrystallization cycles.

Reference:
M. Thielen et al., Landau theory for stress-induced order-disorder transitions in phase change materials
Phys. Rev. B 89, 054101 (2014),
DOI: 10.1103/PhysRevB.89.054101