Imaging quantum spin Hall edges in monolayer WTe₂

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Two-dimensional (2D) topological insulators exhibit the quantum spin Hall (QSH) effect, characterized by protected edge conducting channels.
• Recent experimental evidence suggested QSH effect in monolayer Tungsten Ditelluride (WTe2).

Purpose of the Study:

• To directly image and confirm the local conductivity of monolayer WTe2.
• To investigate the behavior of edge conduction under varying conditions like temperature and magnetic field.
• To understand the role of domain boundaries in edge state formation.

Main Methods:

• Microwave impedance microscopy was employed to directly visualize local conductivity.
• Measurements were conducted on monolayer WTe2 samples at temperatures up to 77 K and above.
• Gate voltage and magnetic field dependencies of edge conductivity were analyzed.

Main Results:

• Direct imaging confirmed conduction is strongly localized to the physical edges of monolayer WTe2.
• Edge conductivity exhibited no energy gap as a function of gate voltage.
• Magnetic fields suppressed edge conductivity as predicted by theory.
• Observed conducting features were attributed to edge states at topological domain boundaries.

Conclusions:

• The study provides definitive experimental evidence for the quantum spin Hall effect in monolayer WTe2.
• The robustness and engineerability of QSH channels in WTe2 are highlighted.
• Findings are critical for the interpretation and advancement of WTe2-based electronic devices.