Organically Made Quantum Spin Liquids
The spin-1/2 atoms in a so-called quantum spin liquid form a liquid-like magnetic state in which spins never order as a unit. The phase has been linked to certain forms of superconductivity and might be useful for quantum computing. But quantum spin liquids have been observed in only a handful of materials. Theorists at the University of Tokyo suggest looking for them in a new kind of system: crystals known as metal-organic frameworks (MOFs), in which spin-bearing metal ions are linked by organic molecules.
The team focused on a spin liquid model, proposed by Alexei Kitaev in 2006, that is considered attractive for quantum computing. Here, spin-1/2 atoms are arranged in a honeycomb lattice, and each spin couples to its three neighbors. These couplings “ask” the spin to align along three different directions, making ordering impossible. Some iridium-based oxides are thought to fit this description, though experimentalists have so far found evidence for the Kitaev spin liquid in only one compound, (which does not contain iridium).
Departing from the focus on inorganic solids, Masahiko Yamada and his colleagues proposed a MOF whose metal ions (such as ruthenium) are each surrounded by a “cage” of oxygen ions. These cages would be connected by organic ligands to form six-sided rings. Based on density-functional-theory calculations, the team estimates that the spins in this honeycomb MOF, which chemists are trying to grow, would form a Kitaev quantum spin liquid below 1 K. The researchers also suggest that, since MOFs can grow in a variety of structures, chemists might be able to synthesize an exotic 3D version of the Kitaev phase.
This research is published in Physical Review Letters.
–Jessica Thomas
Jessica Thomas is the Editor of Physics.