Quantum mechanical nature of magnetic charge dynamics in artificial honeycomb ice*

Magnetic charges, arising due to the non-vanishing magnetic fluxes on Kagome vertices, are at the core of emergent novel phenomena in artificial magnetic honeycomb lattices. We have unveiled the quantum mechanical nature of magnetic charge dynamics in honeycomb ice via neutron spin echo measurements on an artificial magnetic honeycomb lattice of permalloy elements of nanometer size. It is found that the magnetic charge dynamics in honeycomb ice is self-propelled and insensitive to the thickness of the honeycomb in the range studied. The quantized charge dynamics is manifested in both time and space. Magnetic charges relax at around 20 ps time scale, comparable to Dirac's monopole's dynamics in atomistic spin ice. Most importantly, magnetic charge dynamics prevails at low temperature, confirming its temporal quantum characteristic. In addition, magnetic charge relaxations localize at distinct wave-vectors corresponding to the integral multiples of honeycomb element length, suggesting its spatial quantization. The observed quantum nature of magnetic charge dynamics is supplemented by first principal quantum mechanical calculation. Finally, we will discuss the implication of our findings in broader perspective in artificial spin ice research.