Discovery of BKT correlations in a kagome compound published in Physical Review Letters

M. Grbić, I. Jakovac and I. Kupčić discovered that in Cs2Cu3SnF12 compund (with a kagome crystal lattice) at temperatures above 20 K, below which the system transitions to an antiferromagnetic state, freely traveling magnetic defects, so-called vortices and antivortices, appear. These topological structures in two dimensions were first predicted in 1973 by V. Berezinskii, J. M. Kosterlitz and D. J. Thouless (BKT). This is the first time that BKT correlations have been found in a compound with a frustrated kagome lattice. So far, only a few cases have been recorded in spin systems, and of those in only one frustrated system (with a triangular lattice). While in all previous systems BKT correlations are typically localized within a narrow temperature range above the magnetic transition, in this compound they exist in a wide temperature range (more than 100 K). Interestingly, the BKT correlations appear together with the onset of short-range chiral order previously detected by neutron scattering.

The system was studied using nuclear magnetic and quadrupolar resonance techniques and all measurements were done at the Department of Physics of the Faculty of Science. The results clearly show the onset and evolution of short-range order, and the paper also revises the magnetic structure that forms below 20 K.

The paper has been accepted for publication in Physical Review Letters.