Negative Capacitance Revisited: A Unified Framework Based on Synchronization, Temporal Delay, and Spatial/Quantitative Mismatch

Negative capacitance (NC) has been reported across a wide range of physical systems, yet its interpretation has remained fragmented due to the absence of a unified conceptual framework. Existing explanations—spanning ferroelectric free‑energy curvature, tunneling transport, plasmonic resonances, and electronic compressibility—have often been treated as unrelated or even contradictory. This review resolves these inconsistencies by demonstrating that all manifestations of NC arise from —non‑synchronization—between external excitation and internal response. We classify NC into three fundamental categories: temporal mismatch, originating from delays or inertia in charge or polarization dynamics; spatial mismatch, caused by nonuniform field or mode distributions; and quantitative mismatch, resulting from intrinsic parameter reversal such as negative curvature or negative compressibility. Despite their diverse physical origins, these mechanisms share the same mathematical signature (C_eff=∂Q/∂V< 0). Organizing NC within this unified framework clarifies long‑standing ambiguities, connects previously isolated research fields, and establishes a systematic foundation for engineering NC in electronic, photonic, and quantum devices. The framework further highlights tunnel‑current‑induced NC as a distinct single‑particle mechanism, expanding the scope of NC beyond ferroelectricity and collective modes. Overall, this work positions NC not as a singular anomaly but as a universal response class emerging from the interplay between excitation and internal dynamics.