Scanning tunnelling microscopy of a two-dimensional magnetic material

Understanding the properties of 2D materials as well as their interactions with each other is important for building heterostructures with tuneable properties. Here, we study the interactions of a 2D magnetic monolayer of CrSe₂ with a graphite substrate by low-temperature Scanning Tunnelling Microscopy (STM) and Spectroscopy. CrSe₂ is a Transition Metal Dichalcogenide, a layered van der Waals material which can exist in either the 1T or distorted 1T’’ structure, characterised by the tetramerization of the Cr atoms. Antiferromagnetic order becomes more favourable than ferromagnetic as the lattice constant and Cr-Cr distance decreases, but whilst the 1T form is metallic, the 1T’’ has a small band gap. Islands of monolayer CrSe₂ are grown on graphite by Molecular Beam Epitaxy. I will discuss topographic and spectroscopic imaging of the morphology and electronic structure of films which exhibit the 1T’’ structure. We observe additional modulations in the CrSe₂ due to a charge-density wave with a periodicity consistent with a Moiré supercell with the graphite surface at 19° relative rotation. From quasiparticle interference imaging we find a linear band dispersion qualitatively similar to the Dirac cones of graphene. We model the heterostructure by Density Functional Theory (DFT) calculations and compare the electronic structure obtained from DFT with the dispersion observed in quasiparticle interference.