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 accompanied 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.

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 accompanied 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.

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 accompanied 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.

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 accompanied 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.