Researchers are developing a new class of quantum-critical metal that can improve electronic devices.

A new study conducted by Qimiao Xi from Rice University discovered a new class of quantum-critical metal, sheding light on complex electron interactions inside quantum materials. The study, published in the journal Physical Review Letters on September 6, explores the effects of interaction between Condo and chiral spin fluids in certain lattice structures.

"The information obtained as a result of this discovery may lead to the development of electronic devices with extreme sensitivity due to the unique properties of quantum-critical systems," said C, Professor of Physics and Astronomy Harry K. and Olga K. Wiss, Director of the Rice Alliance for Extreme Quantum Materials.

Quantum phase transitions

This study is based on the concept of quantum phase transitions. Just as water passes from the solid state to the liquid and gaseous state, electrons in quantum materials can pass from one phase to another as their environment changes. But unlike water, these electrons are subject to the rules of quantum mechanics, which leads to much more complex behavior.

Quantum mechanics represents two key effects: quantum fluctuations and electronic topology. Even at absolute zero, when thermal fluctuations disappear, quantum fluctuations can still cause changes in the organization of electrons, leading to quantum phase transitions. These transitions often lead to extreme physical properties known as quantum criticality.

Moreover, quantum mechanics gives electrons a unique property associated with topology, a mathematical concept that, when applied to electronic states, can cause unusual and potentially useful behavior.

The study was conducted by the Xi group in long-term cooperation with Silke Pashen, co-author of the study and professor of physics at the Vienna University of Technology, and its research group. Together they developed a theoretical model to study these quantum effects.

Theoretical model

Researchers have considered two types of electrons: some move slowly like cars stuck in a traffic jam, and others move quickly in the highway. Although slow-moving electrons seem motionless, their spins can be directed in any direction.

"Usually these rotations form an ordered pattern, but the grid they occupy in our model does not allow such accuracy, which leads to geometric violations," said C.

Instead, the spins form a more fluid structure known as a quantum spin fluid, which is chiral and chooses the direction in time. When this spin fluid connects to fast-moving electrons, a topological effect occurs.

The research team found that this connection also causes a transition to the Kondo phase, where the spins of slow electrons are captured by fast. The study reveals a complex interaction between electron topology and quantum phase transitions.

Ordinary electric transport

When electrons pass through these transitions, their behavior changes dramatically, especially in the way they conduct electricity.

According to Pashen, one of the most important discoveries concerns the Hall effect, which describes how an electric current bends under the influence of an external magnetic field.

"The Hall effect contains a component that is activated by electronic topology," she said. "We show that this effect is experiencing a sudden jump through the quantum critical point."

Implications for future technologies

This discovery expands our understanding of quantum materials and opens up new opportunities for future technologies. According to C, an important part of the discovery of the research team is that the Hall effect reacts sharply to the quantum phase transition.