Physicists from Rice University, Vienna University of Technology, Los Alamos National Laboratory, and Radboud University have discovered a method to switch the topological state of a quantum material on and off using a magnetic field. This breakthrough, published in Nature Communications, could have significant implications for quantum computing and materials research. The researchers, including Qimiao Si of Rice University and Silke Bühler-Paschen of Vienna University of Technology, found that the topological state in a strongly correlated metal could be activated and deactivated, potentially leading to new applications in sensor technology and quantum computers.
Quantum Material’s Topological State Successfully Altered
For the first time, physicists from the U.S. and Europe have discovered a method to switch the topological state of a quantum material on and off. Topological states are crucial in materials research and quantum computing due to their extreme stability and immutable features that cannot be erased or lost to quantum decoherence. The researchers from Rice University, Austria’s Vienna University of Technology (TU Wien), Los Alamos National Laboratory and the Netherlands’ Radboud University published their method in Nature Communications. They used a magnetic field to activate and deactivate a topological state in a strongly correlated metal.
Topological properties are typically found in insulating materials with weak electron correlations. However, the material studied in this research is metallic and strongly correlated. Strongly correlated quantum materials are those where the interactions of a vast number of electrons give rise to collective behaviors like unconventional superconductivity or electrons that behave as if they have more than 1,000 times their normal mass.
The Weyl-Kondo Semimetal: A New State of Matter
The research groups of Qimiao Si from Rice University and Silke Bühler-Paschen from TU Wien have previously made significant discoveries on topological states in strongly correlated quantum materials. In 2017, Si’s theoretical group found a metallic topological state caused by the quintessential example of strong-correlation physics called the Kondo effect. Bühler-Paschen’s experimental group observed the state in a composite material made of cerium, bismuth and palladium. The two teams named the strongly correlated state of matter a Weyl-Kondo semimetal.
In the recent study, Bühler-Paschen’s team found that small impurities or external disturbances did not significantly change the material’s topological properties. However, the application of a laboratory-scale external magnetic field could.
The Role of Strong Electron Correlations
The strong electron correlations make the Weyl-Kondo semimetal extremely responsive to external probes such as a magnetic field. Electrons do not experience the effect of an external magnetic field individually. Instead, they organise collectively, which drastically amplifies the materials’ response to the external magnetic field.
The metallic nature of the topological state lends itself to versatile means of control. The Weyl-Kondo semimetal has charge carriers described by physicist Hermann Weyl’s 1929 relativistic wave equation, which dictates that they come in two varieties with opposite chirality. Like particles of matter and antimatter, Weyl fermions with opposite chirality annihilate one another if they collide.
Switching Off the Topological State
Without electron correlations, it would be impossible to generate a magnetic field with enough strength to push together Weyl fermions of opposite chirality. However, strong correlations in the Weyl-Kondo semimetal allowed Bühler-Paschen’s team to use an external field to force the Weyl fermions to annihilate one another, thus switching off the topological state.
Bühler-Paschen noted that these stable, robust properties can be selectively turned on and off. This switchable topological state could potentially be used for sensor technology.
Potential Applications in Quantum Computing and Electronics
Strong correlations cause the Weyl fermions to couple with radiation in the microwave range, which is particularly important for many technical applications. The technology might also be used for more exotic applications in electronics, including quantum computers. The research at Rice was supported by the National Science Foundation, the Air Force Office of Scientific Research and The Welch Foundation.
“Topological properties are usually found in insulating materials with weak electron correlations,” said Rice study co-author Qimiao Si. “The material we study is metallic and is strongly correlated.”
“The strong electron correlations make the Weyl-Kondo semimetal extremely responsive to external probes such as a magnetic field,” said Si, Rice’s Harry C. and Olga K. Wiess Professor of Physics and Astronomy. “Electrons do not experience the effect of an external magnetic field individually. Instead, they organize collectively, which drastically amplifies the materials’ response to the external magnetic field.”
“You can even make them disappear completely at a certain point,” Bühler-Paschen said. “So we have stable, robust properties that you can selectively turn on and off.”
Si said strong correlations cause the Weyl fermions to couple with radiation in the microwave range, which is particularly important for many technical applications. He said the technology might also be used for ”entirely new, more exotic applications in electronics,” including quantum computers.
Summary
“Physicists from the U.S. and Europe have discovered a method to switch the topological state of a quantum material on and off using a magnetic field, a significant development in quantum computing and materials research. This breakthrough could potentially be used in sensor technology and more exotic applications in electronics, including quantum computers.”
- For the first time, physicists from the U.S. and Europe have discovered a method to switch the topological state of a quantum material on and off. This is significant as topological states are extremely stable and play a crucial role in quantum computing.
- The research was conducted by scientists from Rice University, Austria’s Vienna University of Technology (TU Wien), Los Alamos National Laboratory and the Netherlands’ Radboud University. The method involves using a magnetic field to activate and deactivate a topological state in a strongly correlated metal.
- The study was co-authored by Qimiao Si of Rice University and Silke Bühler-Paschen of TU Wien. They have previously made significant discoveries on topological states in strongly correlated quantum materials.
- The material studied is metallic and strongly correlated, meaning the interactions of billions of electrons give rise to collective behaviours. This is a new area of investigation for physicists who have traditionally studied topological materials.
- The research found that small impurities or external disturbances did not significantly change the material’s topological properties, but the application of a laboratory-scale external magnetic field could.
- The switchable topological states could potentially be used for sensor technology and more exotic applications in electronics, including quantum computers.