Intrinsic Ultrafast Edge Photocurrent Dynamics in WTe₂ Driven by Broken Crystal Symmetry

Area of Science:

• Condensed Matter Physics
• Materials Science
• Nanotechnology

Background:

• Directional photocurrents in 2D materials are key for high-speed, bias-free photodetection.
• Tungsten ditelluride (WTe2) shows symmetry-breaking-induced edge photocurrents from competing mechanisms.
• The intrinsic dynamics of these photocurrents have been experimentally challenging to access.

Purpose of the Study:

• To directly resolve subpicosecond edge photocurrent dynamics in WTe2.
• To investigate the temperature-dependent behavior of photocurrents from 300 K to 4 K.
• To understand the mechanisms behind ultrafast optical-to-electrical conversion and photocurrent switching.

Main Methods:

• Utilized ohmic contacts for precise measurement of edge photocurrents in WTe2.
• Employed ultrafast optical techniques to probe dynamics at subpicosecond timescales.
• Conducted experiments across a wide temperature range (300 K to 4 K).

Main Results:

• Demonstrated ultrafast optical-to-electrical conversion with a 3 dB bandwidth of approximately 250 GHz.
• Observed picosecond-timescale switching of the net photocurrent direction below 150 K.
• Linked the transient bipolar response to nonequilibrium Seebeck effects from asymmetric electron and hole cooling.

Conclusions:

• Revealed previously hidden ultrafast dynamics in symmetry-engineered 2D materials like WTe2.
• Provided new strategies to disentangle competing photocurrent mechanisms.
• Paved the way for developing self-powered, ultrafast optoelectronic devices.