Scientists from the Professorship of Analysis of Solid Surfaces (Head: Prof. Dr. Christoph Tegenkamp) and the Professorship of Experimental Physics focused on Technical Physics (as Head: Prof. Dr. Thomas Seiler) “Proximity-Induced Correlation Effects in Low-Dimensional Structures (FOR 5242)“.
a A recent publication In reputed journal Advanced material interfaces, first author Dr. A research team led by Philip Schadlich presents a method for the detailed structural analysis of two-dimensional layers produced for the first time. The presented approach made it possible to produce samples of sufficient quality to comprehensively describe the structures. New insights from basic research will be relevant in the development of new electronic systems and the development of quantum materials for quantum computing.
“Our synthesis, careful data analysis by various groups, has now achieved this comprehensive picture of two-dimensional lead layers,” says Philip Schadlich. “The controlled coupling of functionalized graphene with 2D electron gases opens up the possibility to investigate and control correlation effects and mesoscopic phenomena in 2D materials – for example superconductivity, spin or charge density waves, and new magnetic phases,” says Seiler.
To investigate these types of systems, researchers funded by the German Research Foundation (DFG) work across departments and locations. Participants from Jülich, Lund (Sweden), Hamburg, Regensburg, Göttingen, Stuttgart and Braunschweig participated. “A high degree of mixing with different professional skills in our research group is necessary to be able to explore all aspects of such complex problems in detail. Only in this way can the structural and electronic properties of self-made systems be connected,” spokeswoman for the DFG research group Prof. Dr. Christoph Tegenkamp says.
Nature’s strategy: domain boundaries in response to unsaturated bonds
“The structure formation of the 2D lead layer is based on patterns we know from previous experiments on lead adsorption on silicon surfaces,” said Dr. Philip Schadlich explains. However, the flexibility of lead bonds leads to a great diversity in the phase diagram, for which the term “devil’s staircase” has been coined.
In contrast, in the present experiment, the lattice mismatch between the substrate and the lead layer results in a reduction of lead atoms for each silicon atom in the substrate, leading to strains in the lead and unsaturated bonds on the substrate surface.
Researchers now know why: “It’s a trick of nature. The lead layer forms domains where the lead atoms relax locally to their preferred distance, and the total offset between the lead and the substrate lattice is not very large,” Schadlich explains. “To do this, the centers of neighboring domains must be slightly offset from each other, so that the boundaries of the domains contain enough lead atoms to automatically compensate for all unsaturated bonds,” Prof. Chitran Ghoshal, a doctoral student in Tegenkamp’s working group, explains.
Greater importance of domain boundaries
The composition of the lead layer also has an effect on graphene. This is because evaluation of the data showed a vanishingly low charge carrier concentration, which is 1000 times lower than that of epitaxial graphene. “Unlike significantly more efficient intercoolants such as hydrogen, the lead layer manages to protect or compensate for the natural polarization of the substrate, thus providing quasi-charge neutrality,” continues Ghoshal.
Also, with the help of scanning tunneling microscopy at temperatures as low as four Kelvin (about -269 degrees Celsius), Kekule revealed the fingerprint of the so-called ground state. Here again, domain boundaries play an important role, as electrons are scattered across them and, due to charge neutrality, only limited phase space is available.
Background: DFG Research Group “Proximity-Induced Correlation Effects in Low-Dimensional Structures” led by Chemnitz University of Technology
Phenomena such as those currently described by Prof. The DFG, led by Tegenkamp, is at the heart of the research group. Funded with more than four million euros, the research team has dedicated itself to investigating correlation effects in 2D materials and has brought together the expertise of eight working groups from across Germany. The goal is to manipulate 2D materials in a targeted manner, thereby researching exotic effects such as superconductivity, charge density waves, Mott states, the quantum Hall effect, and Klein tunneling.
Advanced material interfaces
Title of the article
Domain boundary formation within an intercalated Pb monolayer featuring charge-neutral epitaxial graphene
Date of publication of the article
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