Negative Quantum Capacitance-Driven Photonic Synapse with Ultralow Energy Consumption and Year-Scale Retention.

Area of Science:

• Materials Science
• Condensed Matter Physics
• Nanotechnology
• Neuromorphic Engineering

Background:

• Conventional computing architectures face energy and latency limitations for emerging neuromorphic systems.
• There is a need for devices that integrate sensing, memory, and computing functionalities.
• Two-dimensional (2D) van der Waals heterostructures offer promising platforms for novel electronic and optoelectronic devices.

Purpose of the Study:

• To introduce a novel two-dimensional van der Waals photonic synapse.
• To investigate the role of quantum effects, specifically negative quantum capacitance, in enhancing synaptic device performance.
• To demonstrate the device's capability in performing essential synaptic functions and applications for neuromorphic computing.

Main Methods:

• Fabrication of a 2D van der Waals photonic synapse using MoS₂/h-BN/WTe₂/h-BN heterostructure.
• Utilized Weyl semimetal (WTe₂) as a floating gate, tuning the Fermi level near Weyl nodes via charge tunneling.
• Characterized the device's synaptic functions, including retention, response time, and energy consumption, and demonstrated its application in handwritten-digit classification.

Main Results:

• The device exhibits a negative quantum capacitance effect due to enhanced electron-electron correlation near Weyl nodes.
• This quantum effect amplifies the gate voltage, creating a strong built-in electric field for improved performance.
• Achieved long retention (approaching one year at room temperature) and ultralow energy consumption (0.26 fJ per event) for synaptic operations.

Conclusions:

• Quantum effects, particularly negative quantum capacitance, provide a robust pathway for developing ultralow-energy, long-retention neuromorphic devices.
• The demonstrated photonic synapse successfully mimics synaptic functions and performs artificial neural network tasks.
• This work highlights the significant potential of integrated optoelectronic computing enabled by quantum phenomena in 2D materials.