An artist's illustration of heavy fermion physics in the new ultra-thin two-layer material. Image: Heikka Valja.Researchers at Aalto University in Finland have created a new ultra-thin two-layer material with quantum properties that normally require rare earth compounds. This material, which is relatively easy to make and does not contain rare earth metals, could provide a new platform for quantum computing and advance research into unconventional superconductivity and quantum criticality.
Reporting in a paper in Nature, the researchers showed they can produce a radically new quantum state of matter from seemingly common materials. Their discovery emerged from efforts to create a quantum spin liquid for investigating emergent quantum phenomena such as gauge theory. This involved fabricating a single layer of atomically thin tantalum disulphide, but the fabrication process also created islands consisting of two layers.
When the team examined these islands, they found that interactions between the two layers induced a phenomenon known as the Kondo effect, leading to a macroscopically entangled state of matter producing a heavy-fermion system.
The Kondo effect is an interaction between magnetic impurities and electrons that causes a material’s electrical resistance to change with temperature. This results in the electrons behaving as though they have more mass, producing what are called heavy fermion materials. This phenomenon is a hallmark of materials containing rare earth elements.
Heavy fermion materials are important in several domains of cutting-edge physics, including research into quantum materials. "Studying complex quantum materials is hindered by the properties of naturally occurring compounds. 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 realized in the lab," says Peter Liljeroth, a professor at Aalto University.
For example, heavy fermion materials could act as topological superconductors, which could be useful for building qubits that are more robust to noise and perturbation from the environment, reducing error rates in quantum computers. "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," explains Viliam Vano, a doctoral student in Liljeroth’s group and the paper’s lead author.
Although both layers in the new material are tantalum sulphide, there are subtle but important differences in their properties. One layer behaves like a metal, conducting electrons, while the other layer has a structural change that causes electrons to be localized into a regular lattice. The combination of the two layers results in the appearance of heavy fermion physics, which neither layer exhibits alone.
This new heavy fermion material also offers a powerful tool for probing 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, a professor at Aalto University. "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."
"In the future, we will explore how the system reacts to the rotation of each sheet relative to the other and try to modify the coupling between the layers to tune the material towards quantum critical behaviour," says Liljeroth.
This story is adapted from material from Aalto University, with editorial changes made by Materials Today. The views expressed in this article do not necessarily represent those of Elsevier. Link to original source.