For several years, rare-earth compounds have been gaining the attraction of scientists because of their special quantum properties, which have remained out of the reach of regular compounds until now.
Schematic of how heavy fermions form in twisted graphene sheets. Image Credit: Jose Lado, Aalto University.
One of the most exotic and exceptional properties of such materials is the occurrence of exotic superconducting states, and specifically, the superconducting states needed to construct futuristic topological quantum computers.
For decades, researchers have been aware of these specific rare-earth compounds, called heavy fermion superconductors. However, creating usable quantum technologies out of them has been a crucially open challenge.
The reason is such materials contain crucially radioactive compounds, like plutonium and uranium, which restricts their use in real-world quantum technologies.
At present, a new study has come up with an alternative means to engineer the basic phenomena of such rare-earth compounds using only graphene, which does not present any of the safety issues of conventional rare-earth compounds.
The interesting finding of the new study demonstrates how a quantum state called a “heavy fermion” can be generated by integrating three twisted graphene layers. A heavy fermion is a particle—in this instance an electron—that acts like it has a lot more mass compared to what it does. This property arises from special quantum many-body effects that were mostly observed only in rare-earth compounds so far.
Such a heavy fermion behavior is considered to be the driving force of the phenomena that is needed to use these materials for topological quantum computing. The new findings illustrate a new and non-radioactive technique of achieving this effect by using only carbon, thereby opening the door for sustainably exploiting heavy fermion physics in quantum technologies.
The scientists demonstrate the possibility to make heavy fermions with inexpensive and non-radioactive materials. They achieved this by using graphene, which is a one-atom-thick layer of carbon. This study was authored by Aline Ramires (Paul Scherrer Institute, Switzerland) and Jose Lado (Aalto University).
Although graphene is chemically similar to the material used in regular pencils, its sub-nanometer thickness implies that it possesses special electrical properties. The researchers layered the thin sheets of carbon on top of one another in a particular pattern, where each sheet is rotated with respect to the other, and developed the quantum properties effect that makes the electrons in the graphene act like heavy fermions.
Until now, practical applications of heavy fermion superconductors for topological quantum computing has not been pursued much, partially because it required compounds containing uranium and plutonium, far from ideal for applications due to their radioactive nature.
Jose Lado, Assistant Professor, Aalto University
“In this work we show that one can aim to realize the exactly very same physics just with graphene. While in this work we only show the emergence of heavy fermion behavior, addressing the emergence of topological superconductivity is a natural next step, which could potentially have a groundbreaking impact for topological quantum computing,” added Lado.
Topological superconductivity is of huge interest when it comes to quantum technologies, also addressed by alternative approaches in other papers from Aalto University Department of Applied Physics, which includes an earlier paper by Professor Lado.
These results potentially provide a carbon-based platform for exploitation of heavy fermion phenomena in quantum technologies, without requiring rare-earth elements.
Jose Lado, Assistant Professor, Aalto University
Journal Reference:
Ramires, A & Lado, J L, (2021) Emulating Heavy Fermions in Twisted Trilayer Graphene. Physical Review Letters. doi.org/10.1103/PhysRevLett.127.026401.
Source: https://www.aalto.fi/en