Enhanced Charge-Density-Wave Order and Suppressed Superconductivity in Intercalated Bulk $\mathrm{Nb}{\mathrm{Se}}_{2}$

TL;DR

This study demonstrates that electrochemical intercalation in NbSe₂ can effectively decouple layers, enhance charge-density-wave order, and suppress superconductivity, mimicking monolayer physics in bulk materials.

Contribution

It introduces a scalable intercalation method to control electronic phases in layered materials, enabling exploration of monolayer-like properties in bulk NbSe₂.

Findings

Intercalation doubles interlayer spacing and electronically decouples layers.

Charge-density-wave transition temperature increases to ~130 K.

Superconductivity is strongly suppressed, matching monolayer phase diagrams.

Abstract

The electronic ground states of transition-metal dichalcogenides are strongly shaped by reduced dimensionality, yet the properties of atomically thin layers remain difficult to probe due to their small size and environmental sensitivity. Here we demonstrate that controlled electrochemical intercalation of organic cations provides a robust bulk platform for accessing monolayer-like physics in NbSe$_2$. Intercalation of tetrapropylammonium and tetrabutylammonium expands the interlayer spacing by nearly a factor of two, electronically decoupling the NbSe$_2$ layers while simultaneously introducing well-defined charge doping. Using a combination of Raman spectroscopy, scanning tunneling microscopy, X-ray diffraction, and photoemission, we uncover a pronounced enhancement of the charge-density-wave transition temperature to $\sim 130$ K together with a strong suppression of superconductivity, reproducing the phase diagram observed in exfoliated monolayers. The enhanced charge-density-wave order and reduced $T_c$ arise from the combined effects of dimensionality reduction and electron injection, and are accompanied by distinct dip-hump anomalies in the tunneling spectra suggestive of collective mode excitations. Our results establish molecular intercalation as a powerful and scalable route for engineering competing orders in layered quantum materials.