Van Der Waals Schottky Barriers As Interface Probes Of The Correlation Between Chemical Potential Shifts And Charge Density Wave Formation In 1t-Tise2 And 2h-Nbse2

Layered transition-metal dichalcogenide (TMD) materials, i.e., 1T-TiSe2 and 2H-NbSe2, 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-TiSe2 and 2H-NbSe2 to 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 redistributions and a combination of lattice strain energies and Coulomb interactions. These modulations of chemical potential in CDW systems, such as 1T-TiSe2 and 2H-NbSe2 harboring second-order phase transitions, reflect a corresponding conversion from short-range to long-range order.