Project Details
Projekt
In Search of a Quantum Critical Point - Thermodynamic Investigations of the Superconducting and Strange Metal Phases in Magic-Angle Twisted Bilayer Graphene
Applicant
Professor Dr. Dmitri K. Efetov
Subject Area
Experimental Condensed Matter Physics
Term
since 2024
Project identifier
Deutsche Forschungsgemeinschaft (DFG) - Project number 535146365
The overall research objective of this project is to study the thermodynamics of the formation of correlated electronic phases from the so-called strange metal state through nanoscale heat capacity experiments in magic angle twisted bilayer graphene (MATBG). With such measurements we want to pin point a quantum critical point in the phase diagram of this system, and to obtain microscopic insight into the ordered phases surrounding it. The mechanism of formation of highly ordered states, such as superconductors or magnets, from an incoherent ’strange-metal’ phase near a quantum critical point is a major conundrum reported in a variety of correlated materials, but remains to this day one of the biggest open questions in modern condensed matter physics. The recent discovery of flat bands and demonstration of strong electronic correlations, superconductivity, magnetism and an alleged strange metal phase in 2D magic-angle twisted bilayer graphene, transformed this status quo. Due to its unprecedented tunability, which allows controlling the electronic band structure and position of the Fermi level, it opened up vast new possibilities in the study of these strongly correlated phases, which now allows the study of the emergence of correlated phenomena in fermionic systems, in a continuous manner. In recent years my group has established all the necessary techniques to perform a detailed study of the electronic heat capacity in MATBG, namely the truly pioneering work on the fabrication of MATBG heterostructures and the ability to measure the electronic specific heat of mesoscopic 2D materials by a combination of Johnson-noise thermometry and laser heating. Now, a wide range of nano-scale conductors, in particular MATBG devices, can be measured using this method. The study of the specific heat in the quantum critical state of MATBG may help to unravel the long-standing enigma of the nature of this incoherent metallic background, the strange metal, and its relationship with the superconducting phase. Using MATBG for this study will provide a greatly tunable platform, which will allow to probe a yet unexplored observable in this system: the electronic specific heat. We thus will for the first time perform thermodynamic measurements on a new and unprecedentedly tunable member of the family of strange metals.
DFG Programme
Priority Programmes
