Weird Quantum State of Matter Observed for the First Time

Andrea Bianchi, a physicist, discovered the "quantum spin liquid" condition in a magnetic substance he developed in his lab.

It's not every day that someone in quantum physics discovers a new state of matter in order to better comprehend their characteristics.

An multinational team of researchers has done just that. Andrea Bianchi, a physics professor at the University of Montreal and a researcher at the Regroupement québécois sur les matériaux de pointe, and his students Avner Fitterman and Jérémi Dudemaine make up the team.

The scientists describe a "quantum spin liquid ground state" in a magnetic material made in Bianchi's lab in a recent paper published in the scholarly journal Physical Review X: Ce2Zr2O7 is a cerium, zirconium, and oxygen-based molecule.

Like a liquid locked inside an extremely cold solid

Spin is an intrinsic feature of electrons that is connected to their rotation in quantum physics. Spin is what gives a magnet's material its magnetic characteristics. In some materials, spin results in a disorganized structure similar to that of molecules in a liquid, hence the expression “spin liquid.”

As a material's temperature rises, it gets more disordered. When water transforms into steam, for example, this is the situation. Spin liquids, on the other hand, have the property of remaining disordered even when chilled to absolute zero (–273°C / –459.67°F).

Because the direction of spin continues to fluctuate as the material cools, rather than stabilizing in a solid state as it does in a conventional magnet, where all the spins are aligned, spin liquids remain disordered.

The art of “frustrating” electrons

Consider an electron to be a little compass that may point up or down. The electron spins in conventional magnets are all orientated in the same direction, either up or down, forming a "ferromagnetic phase." This is how you maintain images and messages on your refrigerator.

However, in quantum spin liquids, the electrons create a "ménage à trois" marked by strong turbulence that disrupts their order. As a result, there is no magnetic order and an entangled wave function.

“When a third electron is added, the electron spins cannot align because the two neighboring electrons must always have opposing spins, creating what we call magnetic frustration,” Bianchi noted. “This generates excitations that maintain the disorder of spins and therefore the liquid state, even at very low temperatures.”

So how did they add a third electron and cause such frustration?

Creating a ménage à trois

Bianchi's frustrated magnet Ce2Zr2O7 was made in his lab. We can now add “master of the art of frustrating magnets!” to his already extensive list of accomplishments in producing breakthrough materials like superconductors.

The cerium-based substance Ce2Zr2O7 has magnetic characteristics. 

The cerium-based substance Ce2Zr2O7 has magnetic characteristics. “The existence of this compound was known,” Bianchi stated. “Our breakthrough was creating it in a uniquely pure form. We used samples melted in an optical furnace to produce a near-perfect triangular arrangement of atoms and then checked the quantum state.”

Bianchi and his UdeM team were able to induce magnetic frustration in Ce2Zr2O7 thanks to this near-perfect triangle. They evaluated the compound's magnetic diffusion in collaboration with researchers from McMaster and Colorado State universities, Los Alamos National Laboratory, and Dresden's Max Planck Institute for the Physics of Complex Systems.

“Our measurements showed an overlapping particle function—therefore no Bragg peaks—a clear sign of the absence of classical magnetic order,” Bianchi added. “We also observed a distribution of spins with continuously fluctuating directions, which is characteristic of spin liquids and magnetic frustration. This indicates that the material we created behaves like a true spin liquid at low temperatures.”

From dream to reality

The scientists determined that they were observing a never-before-seen quantum state after confirming their observations with computer simulations.

“Identifying a new quantum state of matter is a dream come true for every physicist,” Bianchi said. “Our material is revolutionary because we are the first to show it can indeed present as a spin liquid. This discovery could open the door to new approaches in designing quantum computers.”

Frustrated magnets in a nutshell

Magnetism is a phenomena in which all of a material's electrons spin in the same direction. The ferromagnet, for example, gets its magnetic characteristics from the alignment of spins. Electrons in close proximity can also spin in opposing directions. The spins have well-defined orientations in this scenario, but there is no magnetism. Frustrated magnets are frustrated because nearby electrons strive to orient their spins in opposite directions, and when they reach a triangle lattice, they can't find a common, stable configuration. As a consequence, a frustrated magnet emerges.