Periodic Reporting for period 2 - DeQ (Quantifying electron-electron forces at the atomic scale)
Reporting period: 2022-07-01 to 2023-12-31
Our demands for digital data storage and information processing increases rapidly, and comes along with challenges on our energy resources required to operate and cool our electronic devices. One promising direction for more sustainable technologies is to utilize quantum phases in novel types of two dimensional (2D) materials. These materials consist of a single layer, typically one to three atoms thick. The restriction to a few atoms in one dimension drastically changes the physical properties, in particular it often results into strong electron-electron interactions. These interactions favor the emergence of novel quantum phases, such as non-collinear magnetism or novel types of insulating material phases. Up to date, the understanding of the role of the interface and dimensionality on the emergence of different quantum phases and the electron-electron interactions is subject to large amount of research. In particular, the determination of the strong and sensitive relationship between atomic-scale structure, charges and spins is required to predict which material classes and combinations yield exotic quantum phases.
The objective of this program is to strive for more predictability of the emergence of quantum phases with strong electron-electron interactions in novel 2D materials. The program aims at understanding the fundamental mechanisms to tune the electron-electron interactions. One goal of the program is to create a new state-of-the-art characterization methodology required to quantify the interplay between the geometric structure, charges and spins at the single-atom level in various quantum phases. Fundamentally, this program would lead to a deeper understanding on the atomic-scale mechanisms relevant for the formation of novel quantum phases. From a societal standpoint, these fundamental findings are highly important for a targeted development of novel quantum phases for more sustainable technologies.
The objective of this program is to strive for more predictability of the emergence of quantum phases with strong electron-electron interactions in novel 2D materials. The program aims at understanding the fundamental mechanisms to tune the electron-electron interactions. One goal of the program is to create a new state-of-the-art characterization methodology required to quantify the interplay between the geometric structure, charges and spins at the single-atom level in various quantum phases. Fundamentally, this program would lead to a deeper understanding on the atomic-scale mechanisms relevant for the formation of novel quantum phases. From a societal standpoint, these fundamental findings are highly important for a targeted development of novel quantum phases for more sustainable technologies.
One goal of the program is to develop a new experimental approach to probe and quantify the geometric structure, charge and spin order at surfaces of 2D materials. For this, we combine several experimental methods, in particular, a novel combination of current and force-based spin-sensing at the atomic scale (called SPEX) that we developed over the course of the past years. At the begin of the program, it was required to benchmark our new approach and contrast it to the results to the current state of the art research. To this end, we determined how the current state of the art method to quantify charge density wave order in 2D materials at the atomic scale compares with our new experimental approach. First, we characterized the demands to our measurement probe and optimized a procedure on how to prepare reliable probes for our measurements. This required a modification of the sample stage. We then characterized the charge density wave in a quasi 2D material using our new experimental approach. Surprisingly, we obtained a different observation than expected which is currently still work in progress. Our findings indicate that our new experimental approach provides highly complementary information on the atomic structure and orbital characterization of charge density waves at the surface of 2D materials.
Another important step for the program was the design of the experimental setup for the implementation of our combined force and current-based approach into magnetic and electric fields. The setup will operate at low temperatures in ultra-high vacuum and in a magnetic field up to 3T. This is highly important to characterize magnetic 2D materials. We further optimized all components of the setup for ultra-clean preparation of atomically-thin layers of material by in-situ MBE growth, which is required for the in-situ preparation of 2D materials. At the same time, we have fast transfer mechanism in the measurement stage for ex-situ prepared 2D materials.
Another important step for the program was the design of the experimental setup for the implementation of our combined force and current-based approach into magnetic and electric fields. The setup will operate at low temperatures in ultra-high vacuum and in a magnetic field up to 3T. This is highly important to characterize magnetic 2D materials. We further optimized all components of the setup for ultra-clean preparation of atomically-thin layers of material by in-situ MBE growth, which is required for the in-situ preparation of 2D materials. At the same time, we have fast transfer mechanism in the measurement stage for ex-situ prepared 2D materials.
We utilized a new combined experimental approach to characterize charge density wave order at surfaces of 2D materials. Our finding indicates that this new approach will be highly valuable for characterizing the geometric and electronic structure in charge density phases in any 2D materials. In the further scope of this project, we aim to extend our new approach to other quantum phases, in particular in correlated 2D insulators and 2D magnetic materials. We further plan to finish the installation and benchmarking of our new experimental setup. In this way, we can explore the interplay of charge order and spins in 2D magnetic materials.