Reversal of charge transfer doping on the negative electronic compressibility surface of MoS2

TL;DR

This study demonstrates negative electronic compressibility in MoS2, leading to a reversal of expected charge transfer behavior with WTe2, highlighting many-body interactions in 2D semiconductors.

Contribution

It reveals how negative electronic compressibility in MoS2 causes a reversal in charge transfer direction with WTe2, a novel insight into many-body effects in TMDs.

Findings

Negative electronic compressibility observed in MoS2 surface.

Reversal of charge transfer behavior between MoS2 and WTe2.

Many-body interactions significantly influence electron behavior in TMDs.

Abstract

The strong electron-electron interaction in transition metal dichalcogenides (TMDs) gives rise to phenomena such as strong exciton and trion binding and excitonic condensation, as well as large negative exchange and correlation contributions to the electron energies, resulting in negative electronic compressibility. Here we use angle-resolved photoemission spectroscopy to demonstrate a striking effect of negative electronic compressibility in semiconducting TMD MoS2 on the charge transfer to and from a partial overlayer of monolayer semimetallic WTe2. We track the changes in binding energy of the valence bands of both WTe2 and MoS2 as a function of surface transfer doping with donor (K) and acceptor (F4-TCNQ) species. Donor doping increases the binding energy of the MoS2 valence band, as expected, while counterintuitively reducing the binding energy of the WTe2 valence bands and core levels. The inverse effect is observed for acceptor doping, where a typical reduction in the MoS2 binding energies is accopanied by an unexpected increase in those of WTe2. The observations imply a reversal of the expected charge transfer; donor (acceptor) deposition decreases (increases) the carrier density in the WTe2 adlayer. The charge transfer reversal is a direct consequence of the negative electronic compressibility of the MoS2 surface layer, for which addition (subtraction) of charge leads to attraction (repulsion) of further charge from neighbouring layers. These findings highlight the importance of many-body interactions for the electrons in transition metal dichalcogenides and underscore the potential for exploring strongly correlated quantum states in two-dimensional semiconductors.