Electron-Phonon Coupling Drives the Gapless Charge Density Wave in Few-Layer 1T-VSe 2

Abstract

The driving mechanism of the charge density wave (CDW) remains debated, particularly between Fermi surface nesting (FSN) and electron-phonon coupling (EPC) scenarios. Here, gate-tunable electrical and thermoelectric transport measurements were used to probe the CDW-related electronic structure in few-layer 1T-VSe 2 . Thickness reduction strongly suppresses the long-range three-dimensional CDW order associated with the bulk transition near 110 K, allowing the high-temperature CDW-related anomaly near 170 K to be resolved in macroscopic transport. Through gate tuning, we find that this CDW-related state does not exhibit signatures of a well-defined Peierls-like gap but instead remains gapless within an intrinsic multiband electronic landscape. In particular, the Seebeck coefficient shows pronounced anomalies at both temperature scales (110 K and 170 K), yet no gap-induced thermoelectric anomaly or gate-dependent gap-opening behavior is observed. These results demonstrate the gapless nature of the CDW state, while the high-temperature 170 K anomaly directly fingerprints the localized precursor lattice softening, collectively providing strong transport evidence that supports electron-phonon coupling over conventional Fermi surface nesting as the dominant driving mechanism. Our work provides a new experimental perspective on the dimensionality-dependent CDW behavior in VSe 2 and establishes thermoelectric transport as a sensitive probe for distinguishing CDW formation mechanisms in low-dimensional materials.