Cornell University researchers have made a groundbreaking discovery in the field of quantum insulators, challenging long-held beliefs and opening up new possibilities for quantum device development. By utilizing magnetic imaging techniques, the researchers were able to directly visualize the movement of electrons in a special type of insulator known as a quantum anomalous Hall insulator. Contrary to previous assumptions, they found that the transport current flows within the material’s interior rather than at its edges.
This discovery brings new insights into the behavior of electrons in quantum anomalous Hall insulators and has the potential to settle a longstanding debate about the flow of current in quantum Hall insulators more broadly. Furthermore, it paves the way for the development of topological materials that can be used in the next generation of quantum devices.
The research, led by assistant professor of physics Katja Nowack, stems from the study of the quantum Hall effect, which was first observed in 1980. When a magnetic field is applied to a specific material, the interior of the bulk sample becomes an insulator while an electrical current moves along the outer edge. This effect is characterized by quantized resistances and a drop in longitudinal resistance to zero.
Quantum anomalous Hall insulators achieve a similar effect by using magnetized materials, resulting in quantization of resistances and the movement of electrons along the edge without dissipating energy. However, the recent findings challenge the prevailing belief that current only flows along the edges in these insulators.
The team focused on a chromium-doped bismuth antimony telluride compound, which is known to exhibit the quantum anomalous Hall effect. Using a sensitive magnetic field sensor called a superconducting quantum interference device (SQUID), the researchers were able to scan the material and reconstruct the current density based on the detected magnetic fields.
To their surprise, they found that the electrons were flowing within the bulk of the material rather than at the boundary edges. This prompted them to delve into old studies and realize that there had been previous debates about the flow of current in quantum Hall insulators.
Nowack hopes that this new perspective will spark further discussion and exploration among researchers working on topological materials. She emphasizes the need to understand the intricacies of current flow in order to fully comprehend these materials.
The implications of this discovery extend beyond fundamental research. It could have implications for the development of hybrid technologies that combine superconductors with quantum anomalous Hall insulators to create even more exotic states of matter.
As Nowack points out, the beauty of topological materials lies in their behavior, which is governed by general principles. However, understanding the microscopic details is essential for both fundamental understanding and practical applications.
The research paper detailing these findings was published in the journal Nature Materials and was authored by Matt Ferguson, Ph.D. ’22, who is currently a postdoctoral researcher at the Max Planck Institute for Chemical Physics of Solids in Germany.
What is a quantum anomalous Hall insulator?
A quantum anomalous Hall insulator is a special type of material that behaves as an insulator in its bulk while allowing the transport of current along its edges. This unique behavior is achieved by using magnetized materials and is characterized by quantized resistances.
What is the quantum Hall effect?
The quantum Hall effect refers to the phenomenon observed in certain materials when a magnetic field is applied. The interior of the material becomes an insulator, while an electrical current moves along the outer edge in a single direction. This effect is characterized by quantized resistances and a drop in longitudinal resistance to zero.
How was the research conducted?
The researchers utilized magnetic imaging techniques and a sensitive magnetic field sensor called a superconducting quantum interference device (SQUID) to directly visualize the movement of electrons in a quantum anomalous Hall insulator. They focused on a specific compound and reconstructed the current density based on the detected magnetic fields.
What are the implications of this discovery?
This discovery challenges previous assumptions about the flow of current in quantum Hall insulators and opens up new possibilities for further research and the development of topological materials. It could also have implications for the creation of hybrid technologies that combine superconductors with quantum anomalous Hall insulators to generate novel states of matter.