Microscopic Understanding of Ultrafast Charge Transfer in van der Waals Heterostructures

Area of Science:

• Materials Science
• Condensed Matter Physics
• Optoelectronics

Background:

• Van der Waals heterostructures exhibit ultrafast charge separation after visible light absorption.
• The microscopic mechanisms behind this phenomenon in WS_{2}/graphene heterostructures are not fully understood.
• This lack of understanding hinders the development of optoelectronic applications.

Purpose of the Study:

• To elucidate the microscopic charge transfer mechanisms in epitaxial WS_{2}/graphene heterostructures.
• To identify the key factors determining the timescale of charge separation and the lifetime of transient states.
• To provide insights for designing efficient light harvesting and detection devices.

Main Methods:

• Time- and angle-resolved photoemission spectroscopy (TARPS).
• Microscopic many-particle theory.
• Investigation of epitaxial WS_{2}/graphene heterostructures.

Main Results:

• Charge separation timescale is dictated by direct tunneling at WS_{2}/graphene band crossings.
• The lifetime of charge-separated states is determined by defect-assisted tunneling via sulfur vacancies.
• Identified interplay between intrinsic and defect-related charge transfer channels.

Conclusions:

• The study reveals specific charge transfer pathways in WS_{2}/graphene.
• Understanding these channels is crucial for optimizing optoelectronic device performance.
• Findings pave the way for designing next-generation light harvesting and detection technologies.