A Gapped Phase in Semimetallic T_d -WTe₂ Induced by Lithium Intercalation

Area of Science:

• Condensed Matter Physics
• Materials Science
• Solid-State Chemistry

Background:

• Tungsten ditelluride (WTe2) is a Weyl semimetal exhibiting diverse correlated electronic behaviors.
• Existing physical and chemical methods allow tuning of WTe2's electronic properties.
• Exploration of novel tuning methods is crucial for discovering new electronic phases.

Purpose of the Study:

• To investigate the electronic phase transitions in WTe2 induced by lithium intercalation.
• To characterize the properties of the newly discovered lithiated phase.
• To explore electrochemical intercalation as a method for tuning 2D materials.

Main Methods:

• In situ Hall measurements to probe carrier density changes during lithium intercalation.
• Theoretical calculations to predict the electronic structure and phase of the lithiated WTe2.
• Polarization-angle-dependent Raman spectroscopy to characterize structural changes.
• Transport measurements to observe resistivity behavior with temperature.

Main Results:

• A new electronic phase in WTe2 was successfully induced by lithium intercalation.
• The new phase exhibits insulating behavior with increasing resistivity upon cooling.
• Carrier density was reduced by two orders of magnitude compared to the pristine Td phase.
• Theoretical calculations suggest a charge density wave (CDW) phase with a bandgap of approximately 0.14 eV.
• Structural analysis revealed significant lattice distortions (around 6%) in the lithiated phase.

Conclusions:

• Electrochemical intercalation of lithium creates a novel gapped electronic phase in WTe2.
• This lithiated phase is characterized by reduced carrier density and a distinct crystal structure, potentially a CDW state.
• Electrochemical intercalation is a potent technique for tuning electron density and phase stability in 2D materials.