A Gate-Tunable Ambipolar Quantum Phase Transition in a Topological Excitonic Insulator

Area of Science:

• Condensed Matter Physics
• Materials Science
• Quantum Phenomena

Background:

• Coulomb interactions in 2D semimetals can create correlated insulating states through exciton condensation.
• Atomic WTe2 monolayers are candidates for 2D topological excitonic insulators (2D TEIs).
• The precise mechanism of 2D bulk gap formation in WTe2, especially the role of Coulomb interactions, is debated.

Purpose of the Study:

• Investigate the mechanism of 2D bulk gap formation in WTe2.
• Explore the role of Coulomb interactions in WTe2's excitonic insulator state.
• Determine the tunability of the 2D TEI state in WTe2.

Main Methods:

• Ambipolar field-effect doping of WTe2 monolayers.
• Measurement of the 2D bulk energy gap.
• Analysis of quantum phase transitions.

Main Results:

• WTe2 exhibits a gate-tunable quantum phase transition.
• The 2D bulk energy gap collapses upon ambipolar field-effect doping.
• The 2D TEI state in WTe2 can be tuned into n- and p-type semimetals.

Conclusions:

• WTe2's 2D TEI state is gate-tunable, offering control over its electronic properties.
• This tunability opens avenues for controlling non-trivial 2D superconductivity.
• Exciton condensation and non-trivial band topology in WTe2 are sensitive to doping levels.