2D strongly correlated materials

Strongly correlated materials are a class of materials whose electronic properties are dictated by strong correlations between electrons. Strong many-body interactions destabilize the (otherwise mundane) ground states of quantum materials, and lead to exotic new states such as charge density waves (CDW) and high-temperature superconductivity. Many such materials are layered; thinning down them to atomic thicknesses reduces screening effects and further enhances electron correlation effects. Dimensionality thus provides a tuning knob to modulate strongly correlated phases in various layered materials.

To this end, we develop new techniques to fabricate strongly correlated materials down to monolayers. Because most such materials are extremely sensitive to tracing amount of water vapor or oxygen, it is thus crucial to make devices of these materials in an inert atmosphere or in vacuum, which preserves their intrinsic properties. In addition, we develop new techniques such as ionic gating, gate-controlled lithium intercalation, and ozone annealing, to tune the charge doping of strongly correlated 2D materials up to 10¹⁴ cm^-2. The unprecedented doping capability enables us to tune the CDW states in few-layer 1T-TaS₂ (Nature Nanotechnology 10, 270–276 (2015); Nature Communications 7, 10956 (2016)) and high-temperature superconductivity in monolayer Bi₂Sr₂CaCu₂O_8+δ (Nature 575, 156–163 (2019)).