Constructing heavy fermions in a NbSe₂ heterostructure

Heavy fermion systems are a fascinating arena for studying multiple competing electronic orders in a strongly correlated system. Almost all heavy fermion systems are found in three-dimensional bulk compounds with heavy rare-earth elements with f-electrons, while only recent work shows that heavy fermions can emerge in artificially engineered van der Waals heterostructures.

Here, we push the concept into lighter compounds without any period 6 elements but only atoms having d-electrons, namely NbSe₂. We construct two-dimentional (2D) heavy fermion system in a simple recipe—in a NbSe₂ heterostructure by coupling the itinerant conduction electrons in 1H-NbSe₂ with the localized moments formed by the charge density wave (CDW) in 1T-NbSe₂. We use low-temperature scanning tunneling microscopy (STM) and spectroscopy (STS) to probe local density of states (LDOS) of the differently stacked heterostructures. This allows us to detect the signatures of heavy fermion physics, namely, the Kondo effect when probing the LDOS of the 1T-side and heavy fermion hybridization gap on the 1H-NbSe₂ side of the heterostructure. This 2D system is an exciting playground for exploring heavy fermion phase diagram compared to bulk compounds, since itinerant electrons and localized magnetic moments are de-coupled into separate two component monolayers and can be engineered separately. This viable alternative artificial system is expected to provide new insights into open questions on heavy fermions.