A 3D quantum spin liquid has been discovered in the vicinity of a member of the langbeinite family. The material’s unique crystalline structure and magnetic interactions lead to an unusual behavior that can be attributed to a region of liquidity. An international team conducted experiments at the ISIS neutron source and employed theoretical modeling on a nickel-langbeinite sample to make this discovery. When spins in a crystal lattice cannot align to reach a minimum energy, it is known as magnetic frustration.
Quantum spin liquids (QSLs) are materials with remarkable properties, including topologically protected phenomena that could be beneficial for future applications such as stable qubits. Initially studied in two-dimensional structures, QSLs can also occur in 3D structures, although less frequently. The search for frustration led to the demonstration of this behavior in langbeinites, a class of materials with a 3D structure. Langbeinites are sulfate minerals that are rarely found in nature, and variations in their composition can also exhibit this behavior.
Artificial langbeinite crystals with the molecular formula K2Ni2(SO4)3 were created for the study. Nickel ions in the structure form entangled trillium lattices, causing magnetic frustration, which is further intensified when an external magnetic field is applied. The magnetic moments of the nickel ions fluctuate in a disordered manner, forming a quantum spin liquid even at low temperatures. Neutron data collected at the ISIS neutron source in Oxford confirmed the quantum spin liquid behavior.
Theoretical modeling led by HZB theorist Johannes Reuther explained the measured data using various methods. Their theoretical phase diagram identified an “island of liquidity” within a strongly frustrated tetratrillium lattice, as confirmed by Monte Carlo simulations conducted by postdoctoral researcher Matias Gonzalez. The interactions between the spins were calculated using a method based on Feynman diagrams developed by Reuther, with the agreement between experimental and theoretical results being surprisingly accurate.
Langbeinites represent a large and relatively unexplored class of materials that could potentially exhibit quantum behavior. The study suggests that exploring quantum phenomena in langbeinites could be worthwhile, with the potential for applications in quantum information. HZB physicist Bella Lake’s team has synthesized new langbeinite materials that could also display 3D quantum spin liquid behavior. While still in the realm of fundamental science, interest in new quantum materials has the potential to make Langbeinite materials relevant for future applications.
