Quantum spin liquids in honeycomb magnets
Martin Klanjšek
Jožef Stefan Institute, Ljubljana, Slovenia
In the last decade, honeycomb magnets based on transition metals have come to the spotlight of the physics community, for two reasons. First, Alexei Kitaev showed in 2006 that a honeycomb lattice of spins 1/2 coupled with bond-dependent Ising interactions exhibits an exact quantum spin liquid ground state with two types of fractional elementary excitations: Majorana fermions and gauge fluxes. And second, it was later theoretically predicted that such a model can be realized in compounds comprising edge-shared structural octahedra forming honeycomb lattice. I will present our nuclear magnetic resonance experiments in two such compounds, a-RuCl3 and BaCo2(AsO4)2. They allowed us to demonstrate a theoretically predicted cubic magnetic field dependence of the spin-excitation gap in a‑RuCl3, directly indicating the presence of Majorana fermions. In BaCo2(AsO4)2, we instead found the energy scale of spin excitations to be linear in the magnetic field, which together with other observables points to the realization of the quantum spin liquid state with Dirac spinon excitations.
