Spectroscopic Identification of Dimensionality-Driven Anticorrelation between Charge-Density-Wave Order and Superconductivity in Ultrathin NbSe2

Abstract

Intertwined electronic orders in low-dimensional quantum materials often evolve in a strongly thickness-dependent manner, yet direct spectroscopic access to their mutual evolution remains a key challenge. NbSe2 is a prototypical layered superconductor in which charge-density-wave order coexists with superconductivity, but spectroscopic signatures of the charge-density-wave state are frequently obscured, limiting direct comparison with superconducting order. Here, we demonstrate all-van der Waals planar tunnel junctions as a spectroscopic platform for simultaneously probing charge-density-wave and superconducting states in NbSe2 from the bulk to the bilayer limit. Temperature-dependent tunneling spectra reveal distinct anomalies associated with charge-density-wave formation and superconducting gap opening, allowing both quantum phase transitions to be tracked within the same device architecture. We find that the charge-density-wave transition temperature increases from ∼34 to ∼56 K as the NbSe2 thickness is reduced from 11L to the bilayer, while the superconducting transition temperature decreases from ∼7.2 to ∼5.4 K. These results reveal a clear anticorrelation between the two ordered states as dimensionality is reduced. Moreover, our spectroscopic studies reveal that the emergence of charge-density-wave order modifies the electronic states of NbSe2 over a broad energy window extending up to ±300 meV, a widely anticipated but previously experimentally inaccessible characteristic. Our results provide comprehensive spectroscopic evidence for the thickness-dependent competition between charge-density-wave order and superconductivity in ultrathin NbSe2 and position planar van der Waals tunnel junctions as a powerful platform for investigating emergent quantum phases in layered materials.