Van der Waals Schottky barriers as interface probes of the correlation between chemical potential shifts and charge density wave formation in 1T-TiSe$_2$ and 2H-NbSe$_2$

TL;DR

This study investigates how van der Waals Schottky barriers can serve as sensitive probes for understanding the relationship between chemical potential shifts and charge density wave formation in layered TMD materials 1T-TiSe$_2$ and 2H-NbSe$_2$, revealing temperature-dependent interface properties.

Contribution

It introduces a systematic method to analyze the interface characteristics of TMD materials with GaAs, linking Schottky barrier parameters to CDW-induced chemical potential shifts and phase transition dynamics.

Findings

Chemical potential shifts correlate with CDW formation.

Temperature-dependent barrier parameters reflect interface changes.

Peak in chemical potential indicates competition during CDW evolution.

Abstract

Layered transition metal dichalcogenide (TMD) materials, i.e. 1T-TiSe$_2$ and 2H-NbSe$_2$, harbor a second order charge density wave (CDW) transition where phonons play a key role for the periodic modulations of conduction electron densities and associated lattice distortions. We systematically study the transport and capacitance characteristics over a wide temperature range of Schottky barriers formed by intimately contacting freshly exfoliated flakes of 1T-TiSe$_2$ and 2H-NbSe$_2$ to \textit{n}-type GaAs semiconductor substrates. The extracted temperature-dependent parameters (zero-bias barrier height, ideality and built-in potential) reflect changes at the TMD/GaAs interface induced by CDW formation for both TMD materials. The measured built-in potential reveals chemical-potential shifts relating to CDW formation. With decreasing temperature a peak in the chemical-potential shifts during CDW evolution indicates a competition between electron energy re-distributions and a combination of lattice strain energies and Coulomb interactions. These modulations of chemical potential in CDW systems, such as 1T-TiSe$_2$ and 2H-NbSe$_2$ harboring second-order phase transitions, reflect a corresponding conversion from short to long-range order.