An international team of scientists has, for the first time, observed a new quantum state of matter. They observed a ‘quantum spin liquid ground state’ in a magnetic material called Ce2Zr2O7. Ce2Zr2O7 is a compound composed of cerium, zirconium, and oxygen.
In quantum physics, spin is an essential property influencing the ordering of electrons. In some materials, spin results in a disorganized structure similar to that of molecules, hence the expression “spin liquid.”
As a material’s temperature rises, it gets more disorganized. When water transforms into steam, for example, this is the situation. On the other hand, Spin liquids have the property of remaining disorganized even when cooled to absolute zero (–273°C).
Because of continuous fluctuations in spin direction as the material cools, spin liquid remains disorganized.
Unlike conventional magnets, where electron spins are all oriented in the same direction- creating a ferromagnetic phase- the electrons in quantum spin liquids are positioned in a triangular lattice and form a “ménage à trois.” This “ménage à trois” is characterized by intense turbulence interfering with their order. The result is an entangled wave function and no magnetic order.
Andrea Bianchi, University of Montreal physics professor, said, “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. This generates excitations that maintain the disorder of spins and therefore the liquid state, even at very low temperatures.”
“Ce2Zr2O7 is a cerium-based material with magnetic properties. The existence of this compound was known. 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.”
This triangular arrangement allowed scientists to create magnetic frustration in Ce2Zr2O7. They also measured the compound’s magnetic diffusion.
Bianchi said, “Our measurements showed an overlapping particle function—therefore no Bragg peaks—a clear sign of the absence of classical magnetic order. 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.”
After verifying their observations with computer simulations, scientists confirmed that they were observing a never-before-seen quantum state.
Bianchi said, “Identifying a new quantum state of matter is a dream for every physicist. 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.”
- E. M. Smith, O. Benton et al. Case for a U(1)π Quantum Spin Liquid Ground State in the Dipole-Octupole Pyrochlore Ce2Zr2O7. DOI: 10.1103/PhysRevX.12.021015