Atomic and Electronic Structure of a Multidomain GeTe Crystal.

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Germanium telluride (GeTe) is a ferroelectric semiconductor with renewed interest due to the giant Rashba effect.
• The development of functional spin field-effect transistors relies on controlling spin textures.

Purpose of the Study:

• Investigate the atomic and electronic properties of GeTe bulk crystals and their (111) surfaces.
• Understand the relationship between ferroelectric domains, surface terminations, and spin polarization.

Main Methods:

• High-angle annular dark-field transmission electron microscopy (HAADF-TEM) for domain boundary analysis.
• Photoelectron diffraction and X-ray photoelectron spectroscopy (XPS) for surface termination identification.
• Spin-resolved angle-resolved photoemission spectroscopy (spin-ARPES) to probe spin polarization.

Main Results:

• Successfully grew GeTe crystals with parallel inversion domains of ~10 nm thickness.
• Identified two types of domain boundaries, one resembling a van der Waals gap.
• Determined preferential Te-termination (~68%) on surfaces, with domain sizes of 10-100 nm.
• Established a quantitative link between bulk spin polarization and surface termination contributions.
• Observed reversal of spin texture in bulk Rashba bands correlating with ferroelectric polarization.

Conclusions:

• The nanostructure and surface properties of GeTe are crucial for controlling spin texture.
• Findings support the potential of ferroelectric Rashba semiconductors for nonvolatile spintronic devices.
• This research paves the way for advanced nanoscale memory and computing.