Germanium telluride (GeTe) is a ferroelectric Rashba semiconductor with many interesting properties. The crystals are made of nanodomains whose ferroelectric polarization can be changed by an applied electric field. This ferroelectric property can also be used to change the spin of electrons in each domain, thanks to the so-called Rashba effect. Germanium telluride is therefore an interesting material for use in spintronic devices, allowing data processing with significantly less energy input.
Now, HZB and a team from Lomonosov Moscow State University have set up a joint Helmholtz-RSF research group to provide comprehensive insights into the material at the nanoscale. The team was led by Dr. Rada Yashner, a physical chemist at Lomonosov State University, and Dr. Jaime Sanchez-Bariga, an HZB physicist. “We examined the material using a variety of state-of-the-art methods, determining not only its atomic structure, but also the internal connections of its atomic and electronic structures at the nanoscale,” says Radha Yashna, who produces high-quality crystal samples in her lab.
Their microscopic studies showed that the crystals had two different types of boundaries around ferroelectric nanodomains, which ranged in size from 10 to 100 nanometers. At BESSY II, the team was able to observe two surface ends with opposite ferroelectric polarization and analyze how these correspond to nanodomains of Ge or Te atoms in the topmost layer of the surface.
“In BESSY II, we were able to precisely analyze the insertion relationship between spin polarization in vivo or on the surface and the opposite ferroelectric polarization configuration,” explains Jaime Sanchez-Barriga. The scientists also determined how the spin texture is switched by ferroelectric polarization within a single nanostructure. “Our results are important for potential applications of ferroelectric Rashba semiconductors in nanoscale non-volatile spintronic devices,” Sanchez-Barriga stressed.