A research study carried out by an international team comprising Dr. Shigeki Onoda from the Condensed Matter Theory Lab at the RIKEN Advanced Science Institute, Dr. Yixi Su from the Jülich Center for Neutron Science JCNS-FRM II at Forschungszentrum Jülich and Dr. Lieh-Jeng Chang belonging to the Japan Atomic Energy Agency and Physics Department of the National Cheng Kung University has yielded nominal evidence of Higgs transition of monopoles of electron spins in a magnet, Yb2Ti2O7 at an absolute temperature of 0.21 K.
"Neutron-scattering intensity map at 0.3 K (Copyright: Riken)
Left: Experimental result on Yb2Ti2O7.; Middle: Theoretical results based on the quantum spin ice model; Right: A map for conventional magnets slightly above a magnetic transition temperature"
Most magnetic materials are made up of electrons acting as tiny magnets labeled as spins by virtue of their rotation akin to that of the earth. Cooling leads to the formation of a magnetic order of the spins wherein the spin monopoles are restricted to each other. However, magnetic materials such as spin ice do not form a magnetic order on cooling and exhibit behavior that indicates fractionalization of the monopoles while they are still unstable. As opposed to this, Dr. Onoda and team developed a theoretical model in the period 2010 to 2012 named as quantum spin ice corresponding to magnetic materials Yb2Ti2O7 and Pr2Zr2O7 in which the monopoles achieved a magnetic order by means of Bose-Einstein condensation. The team wanted to establish that cooling would cause the transition of the quantum spin ice magnet from an unstable state of fractionalized monopoles to the state of condensed monopoles. For their experiment, the team irradiated a single crystal of Yb2Ti2O7 with a neutron beam with aligned neutron spins. By studying the pattern of intensity of the neutron scattering by the electron spin, they were able to determine the electron spin configuration. A measure of the electron spin correlation at a temperature of 0.3 K demonstrated the correctness of the quantum spin ice model. At a temperature below 0.21 K, the scattering pattern indicated the loss of neutron spin polarization and formation of magnetic order thereby establishing the transition into a ferromagnetic state. This state is important in achieving control of magnets for various applications.