Existence of Heavy Fermion Behavior in a van der Waals Layered Material

Heavy fermion materials, where localized magnetic moments strongly interact with itinerant electrons, are hosts to a wide variety of emerging quantum phenomena, such as unconventional superconductivity, quantum criticality, and non-Fermi liquid behavior. One major challenge in the field is reducing the dimensionality of heavy fermion systems, which offers unique opportunities to tune the Coulomb interactions in ways that are not possible in 3D crystals and could provide new insights into the interplay of electron localization, magnetism, and Coulomb screening. This talk will discuss our recent progress in developing and characterizing a new class of two-dimensional (2D) heavy fermion materials. While these materials are conceptually related to traditional intermetallic heavy fermion compounds, their layered van der Waals (vdW) structures allow for mechanical exfoliation down to atomically-thin flakes. We report bulk measurements, including heat capacity, magnetism, electrical transport, and spectroscopy to demonstrate that this compound is the first example of an intrinsic 2D heavy fermion system. In addition, this material displays complex magnetism due to a triangular lattice of antiferromagnetically ordered atoms, producing a magnetically frustrated lattice with an incommensurate propagation vector. By varying the thickness of the material using mechanical exfoliation, this new system offers the unique opportunity to interrogate the fundamental relationship between dimensionality, magnetism, and heavy fermion behavior and offers a new handle for probing quantum criticality.