At the edge where two exotic materials meet, scientists have discovered a completely new quantum state of matter. Called a “quantum liquid crystal,” this strange phase doesn’t follow the rules of solids, liquids, gases, or even plasma.
Instead, it behaves according to its own symmetry-breaking logic, and could one day help power ultra-sensitive quantum technologies that operate in extreme environments.
Where Quantum Worlds Collide
The Rutgers-led study, published June 13 in Science Advances, explored what happens when a conducting material known as a Weyl semimetal comes into contact with a magnetic insulator called spin ice. Each of these materials is exotic on its own. But when layered together into a wafer-thin sandwich and placed under powerful magnetic fields, the boundary between them revealed unexpected behavior.
“We observed new quantum phases that emerge only when these two materials interact,” said lead author Tsung-Chi Wu, who recently earned his PhD in physics at Rutgers. “This creates a new quantum topological state of matter at high magnetic fields, which was previously unknown.”
Electrons Flow in Strangely Patterned Ways
At the interface of the two materials, the electrons in the Weyl semimetal began to act differently based on direction. This directional behavior, called electronic anisotropy, meant that the material conducted electricity better in some directions than others.
In fact, conductivity dropped sharply at six specific angles within a full 360-degree circle. When the magnetic field was increased further, electrons began flowing in two opposite directions simultaneously—an abrupt shift in symmetry that marked the emergence of a new quantum phase.
This kind of symmetry-breaking is a hallmark of quantum liquid crystals, and suggests rich underlying physics that could lead to useful applications.
Why This Matters
Understanding and controlling the behavior of materials at their interfaces is key to building better quantum devices, especially in fields like sensing, computing, and communications. The Rutgers team believes this discovery could enable new types of sensors that detect magnetic fields in extreme conditions, such as in space or inside high-energy particle accelerators.
“By understanding how electrons move in these special materials, scientists could potentially design new generations of ultra-sensitive quantum sensors of magnetic fields that work best in extreme conditions,” Wu said.
What Are Weyl Semimetals and Spin Ice?
Weyl semimetals are materials where electricity flows almost without resistance due to special particle-like excitations called Weyl fermions. These fermions mimic relativistic particles with no mass, giving rise to unique surface states known as Fermi arcs.
Spin ice, on the other hand, is a magnetic material where magnetic moments—like tiny bar magnets inside each atom—are arranged in a frustrated pattern, similar to the positions of hydrogen atoms in water ice. This unusual magnetic structure gives rise to phenomena like emergent magnetic monopoles and complex spin dynamics.
Key Findings
- When layered, Weyl semimetals and spin ice form a sharp interface where electrons behave differently depending on direction.
- At low temperatures and high magnetic fields, this interface reveals a new quantum liquid crystal phase with broken rotational symmetry.
- Electrons suddenly flow in two opposite directions, marking a dramatic phase shift at 9 Tesla and above.
- The angular magnetoresistance shows a sixfold symmetry at low fields, transitioning to twofold symmetry at high fields.
- These effects are driven by interfacial coupling between mobile electrons and the spin excitations in the spin ice layer.
The Challenge of Building the Interface
Constructing such a complex material stack wasn’t easy. The researchers spent years developing a method to grow atomically sharp layers of Eu2Ir2O7 (the Weyl semimetal) and Dy2Ti2O7 (the spin ice) using pulsed laser deposition and in situ epitaxy.
The interface needed to be nearly perfect to observe the effect. “The ultra-low temperatures and high magnetic fields were crucial for observing these new phenomena,” Wu said. The measurements were conducted at the National High Magnetic Field Laboratory in Tallahassee, Florida.
Team Effort, Deep Modeling
The study was a result of close collaboration between experiment and theory. Wu credited theoretical physicist Jedediah Pixley and postdoctoral researcher Yueqing Chang for helping interpret the complex data. “It took us more than two years to understand the experimental results,” Wu said.
“The experiment-theory collaboration is what really makes the work possible,” he added.
What Comes Next?
By tweaking the materials or replacing the spin ice with a quantum version, the researchers hope to uncover even stranger states of matter. Their work opens the door to exploring heterostructures made of other strongly correlated materials, which could lead to devices that sense, compute, or store information in entirely new ways.
“This is just the beginning,” Wu said. “There are multiple possibilities for exploring new quantum materials and their interactions when combined into a heterostructure.”
And for now, one thing is certain: strange and wonderful things happen where the quantum worlds of magnetism and topology collide.
Journal: Science Advances
Article Title: Electronic anisotropy and rotational symmetry breaking at a Weyl semimetal/spin ice interface
Publication Date: June 13, 2025
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