Identification of strongly correlated spin liquid in herbertsmithite

An exotic quantum spin liquid (QSL) is formed with such hypothetic particles as fermionic spinons carrying spin 1/2 and no charge. Here we calculate its thermodynamic and relaxation properties. Our calculations unveil the fundamental properties of QSL, forming a strongly correlated Fermi system located at a fermion condensation quantum phase transition. These are in good agreement with experimental data and allow us to detect the behavior of QSL as that observed in heavy-fermion metals. We predict that the thermal resistivity of QSL under the application of magnetic fields at fixed temperature demonstrates a very specific behavior. The key features of our findings are the presence of spin-charge separation and QSL formed with itinerant heavy spinons in herbertsmithite.