Subnanoscale Engineering of 2D Magnetism in van der Waals Heterostructures

• Applicants: Professor Dr. Samir Lounis; Professor Dr. Markus Ternes
• Subject Area: Physical Chemistry of Solids and Surfaces, Material Characterisation ; Experimental Condensed Matter Physics ; Theoretical Condensed Matter Physics
• Term: since 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 443405092

Van der Waals (vdW) heterostructures are artificially built structures which combine atomically thin layers with distinct intrinsic properties such as spin-orbit-split electronic bands or superconductivity. These stacks consist of atomically sharp interfaces and can host proximity-enabled physical phenomena that emerge from the non-trivial combination of the constituent layers. The discovery of intrinsically ferromagnetic 2D layers in 2017 supplied one important building block which opened a whole new class of designable vdW heterostructures utilising the spin degree of freedom. In this project, we propose a joint theoretical and experimental characterization of vdW bilayers consisting of a 2D magnetic layer in contact to a layer which possesses large spin-orbit interactions.Our goals for this proposal is to study firstly whether proximity effects from a vdW layer with large spin-orbit interaction can enhance the magnetic anisotropy energy or the magnetic exchange interactions of an 2D magnet, with the goal of raising its ferromagnetic Curie temperature or stabilizing non-ferromagnetic states. Secondly, we plan to reverse the interaction and exploit proximity-induced magnetism from a 2D magnet onto the topological properties of a second layer. To reach our goals we plan to use first-principle methods based on time-dependent density functional theory combined with many-body perturbation theory to compute and explore the electronic, magnetic and transport properties of candidate bilayers with the focus on the magnetic inter- and intralayer interactions. In these calculations we plan to go beyond ground state simulations to access dynamical properties like local spin flip processes as well as collective excitations like magnons and their interactions with electrons. Looking ahead, more complex heterostructures consisting of several layers will also be addressed.Complementary, we plan to assemble bilayers containing a 2D magnet and a layer consisting of relatively heavy elements with strong spin-orbit interaction. Subsequently, we will use low-temperature combined scanning tunneling (STM) and atomic force microscopy (AFM) for a detailed characterization of the structural, electronic, and magnetic properties. Essential here is the unique capabilities of the STM/AFM to obtain information at thenanometer scale which enables us to dive in detail into proximity and edge-effects as well as to detect complexly ordered magnetic structure. We expect that our proposedsymbiosis between theory and experiment will establish the foundation of a new field of vdW heterostructures incorporating 2D magnets.

• DFG Programme: Priority Programmes
• Subproject of: SPP 2244: 2D Materials – Physics of van der Waals [hetero]structures (2DMP)
• Co-Investigators: Dr. Jose Martinez; Dr. Manuel dos Santos Dias