Spin is the intrinsic magnetic moment of a particle—an electron, for example. It is a fundamental magnitude, like mass and charge. Simply put, it is as if the particle had a magnet inside it that enabled it to interact, even while at rest, not only with the spins of other particles but also with external magnetic fields.
Honeycomb lattice with two impurities located in the center of the areas shaded blue. Credit: Eric Andrade/USPBy analogy with usual liquids, a system in which spins do not exhibit magnetic order, even at temperatures close to absolute zero, is termed a spin liquid. In accordance with the same logic, a system with magnetic order is a spin solid, since the magnetic order of its spins is analogous to the periodic order of the atoms in a crystal.Exploration of these systems helps scientists understand fundamental aspects of matter and could lead eventually to an important practical application—topological quantum computing. A considerable research effort is under way in the field for this very reason. An example is the article "Disorder, low-energy excitations, and topology in the Kitaev spin liquid" published in Physical Review Letters."The Kitaev model [formulated by Alexei Yurievich Kitaev, born in Russia in 1963, now a naturalized US citizen and a professor at the California Institute of Technology] is a two-dimensional spin liquid. It's very interesting but somewhat artificial. Deviations from the original model are expected to appear in real materials and that is what we investigated," Eric Andrade, last author of the article, told Agência FAPESP. Andrade is a professor at the University of São Paulo's São Carlos Institute of Physics (IFSC-USP) in Brazil.Andrade and Vitor Dantas, whose Ph.D. research he supervises, studied how Kitaev's model behaves in a honeycomb lattice in the presence of defects and disturbances such as a magnetic field and additional interactions."Since 2009, there have been robust theoretical proposals that the model can be realized in Mott insulators, which exhibit strong spin-orbit coupling," Andrade said.Mott…