Heavy fermion image2 portrait fullres heikka valja

Ultra-thin material mimics quantum entangled rare earth compounds

Finnish physicists have created an ultra-thin, 2D material with quantum properties that would usually only be made possible using rare earth minerals. But this new material was fabricated using only common materials.

“Studying complex quantum materials is hindered by the properties of naturally occurring compounds,” says atomic physicist Peter Liljeroth from Aalto University.

“Our goal is to produce artificial designer materials that can be readily tuned and controlled externally to expand the range of exotic phenomena that can be realised in the lab.”

The team at Aalto University and the University of Jyväskylä, both in Finland, have just published a new Nature paper that describes how the material was made.

Essentially, they fabricated a single layer of atomically thin tantalum disulphide. But during the fabrication process, some parts of the material ended up having two layers, each of which had different properties – one layer behaved like a metal, conducting electrons, while the other forced electrons into a lattice structure.

The interaction between these subtly different layers induced something called the Kondo effect, which caused the material’s electrical resistance to change with temperature (though the relationship is not necessarily linear).

The material’s electrons then behaved as if they had more mass than they really did, producing a heavy fermion system. This is a strongly correlated state of matter that is of great interest to physicists because it can be used to research exotic behaviour in materials, from unconventional superconductivity to quantum criticality.

Usually, such systems are only induced in materials made from rare earth elements – so it’s a boon to find a new heavy fermion material that is easy to synthesise.

Aalto University’s Viliam Vaňo, lead author of the study, explains that research like this could help build more accurate quantum computers, as heavy fermion materials could act as toplogical superconductors – useful for building qubits that aren’t affected by noise from the surrounding environment.

“Creating this in real life would benefit enormously from having a heavy fermion material system that can be readily incorporated into electrical devices and tuned externally,” he says.

The material could also help probe quantum criticality.

“The material can reach a quantum-critical point when it begins to move from one collective quantum state to another – for example, from a regular magnet towards an entangled heavy fermion material,” explains Jose Lado, co-author also from Aalto. “Between these states, the entire system is critical, reacting strongly to the slightest change, and providing an ideal platform to engineer even more exotic quantum matter.”

The team says that this material is not only easier to fabricate than similar systems using rare earth compounds, but it also allows for an unprecedented level of control over the system parameters.

Next, they aim to tweak the material – by changing how the layers are oriented, and how the layers are coupled – to help better explore quantum criticality.