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

Emerging neuromorphic systems demand devices that seamlessly integrate sensing, memory, and computing in a single element to overcome the energy and latency constraints inherent to conventional architectures. Here, we introduce a two-dimensional van der Waals photonic synapse (MoS/h-BN/WTe/h-BN) with the Weyl semimetal (WTe) employed as the floating gate. As the Fermi level is set near the Weyl nodes by a minute charge tunneling, the enhanced electron-electron correlation triggers the negative carrier compressibility and finally results in the negative quantum capacitance effect. This quantum effect amplifies the gate voltage and creates a strong built-in electric field at the h-BN/MoS interface, which benefits both the long-term retention (approaching one year at room temperature) and short-term response (electric energy consumption as low as 0.26 fJ per event) of the photonic synapse. Additionally, the device supports key synaptic functions and applications, including excitatory postsynaptic current potentiation, paired pulse facilitation, logic gate operation, and artificial neural network handwritten-digit classification. These findings establish quantum effects as a robust approach to ultralow-energy, long-retention neuromorphic devices with compelling prospects for integrated optoelectronic computing.