Graphene on titanium carbide triggers a novel phase transition
Graphene-induced Lifshitz-transition from a petal-shaped Fermi surface to a gear-shaped hole Fermi surface revealed by comparative full photoemission mapping of the band structures of bare TiC(111) and graphene/TiC(111). © HZB
Researchers have discovered a Lifshitz-transition in TiC, driven by a graphene overlayer, at the photon source BESSY II. Their study sheds light on the exciting potential of 2D materials such as graphene and the effects they can have on neighboring materials through proximity interactions.
Stacking 2D materials has garnered a lot of attention in recent years as it provides a unique opportunity to tailor material properties in a highly controllable manner. However, the influence of 2D materials on the properties of neighboring materials through proximity effects is not yet fully understood. In particular, very sensitive properties such as band gaps in semiconductors and excitonic properties have been observed to be influenced. Fermi surfaces of bulk metals have so far not been among the properties sensitive to a proximity effect.
The Fermi surface of a metal is a mathematical concept to represent the electrons of the highest energy in the material. Only these electrons participate in properties such as electrical conductivity. An important aspect of the Fermi surface is that it represents them in terms of the direction of their movement.
The new study by Andrei Varykhalov and his colleagues at BESSY II shows that a graphene layer can induce a Lifshitz transition in the near-surface region of an underlying metal, TiC: The Fermi surface transforms from a hole-like to an electron-like Fermi surface. The reported change in Fermi surface character is particularly relevant since it changes the orientation of the movement of the electrons and in the presence of a magnetic field it changes the orientation of the macroscopic electric current.
The present finding is an exciting development as it provides a new avenue for controlling and manipulating the electronic properties of materials, which has implications for a range of technological applications, for example designing materials with quantum properties such as high temperature superconductivity.
- Alternating currents for alternative computing with magnetsA new study conducted at the University of Vienna, the Max Planck Institute for Intelligent Systems in Stuttgart, and the Helmholtz Centers in Berlin and Dresden takes an important step in the challenge to miniaturize computing devices and to make them more energy-efficient. The work published in the renowned scientific journal Science Advances opens up new possibilities for creating reprogrammable magnonic circuits by exciting spin waves by alternating currents and redirecting these waves on demand. The experiments were carried out at the Maxymus beamline at BESSY II.
- BESSY II: Heterostructures for SpintronicsSpintronic devices work with spin textures caused by quantum-physical interactions. A Spanish-German collaboration has now studied graphene-cobalt-iridium heterostructures at BESSY II. The results show how two desired quantum-physical effects reinforce each other in these heterostructures. This could lead to new spintronic devices based on these materials.
- Green hydrogen: MXenes shows talent as catalyst for oxygen evolutionThe MXene class of materials has many talents. An international team led by HZB chemist Michelle Browne has now demonstrated that MXenes, properly functionalised, are excellent catalysts for the oxygen evolution reaction in electrolytic water splitting. They are more stable and efficient than the best metal oxide catalysts currently available. The team is now extensively characterising these MXene catalysts for water splitting at the Berlin X-ray source BESSY II and Soleil Synchrotron in France.