One of the leading models for studying 3D frustrated quantum magnets is the Heisenberg model on a pyrochlore lattice - a simple cubic crystal structure. Nevertheless, it has so far been extremely difficult to derive practical predictions, i.e. for specific materials and temperatures, from this theoretical model.
Teams from Germany, Japan, Canada, and India have now jointly conducted systematic investigations of this model with the aid of a new theoretical method and solved several of these difficulties. It is possible with this new method to vary the spin value of the lattice atoms as well as the temperature and other interaction parameters, and to calculate the parameter ranges in which novel magnetic quantum effects occur. The calculations were carried out at the Leibniz Supercomputing Centre (LRZ) in Munich.
"We were able to show that quantum physical effects surprisingly only occur over very limited parameter ranges", explained theoretical physicist Prof. Johannes Reuther from the Helmholtz-Zentrum Berlin für Materialien und Energie (HZB), co-author of the study. These quantum effects are most pronounced at the smallest possible spin (spin value ½). However, spin systems in the crystal structure investigated by the teams already behave almost completely like classical physical systems at spin values of 1.5 and above.
The work published deepens our understanding of solids and contributes to the systematic advancement of the search for 3D spin fluids in quantum materials.
The study is published Open Access inPhysical Review X(2019) and is titled " Quantum and Classical Phases of the Pyrochlore Heisenberg Model with Competing Interactions ". Yasir Iqbal, Tobias Müller, Pratyay Ghosh, Michel J. P. Gingras, Harald O. Jeschke, Stephan Rachel, Johannes Reuther, and Ronny Thomale are the authors.