Super-Diffusion In Quantum Spin Chains

A drop of ink in a glass of water will diffuse outwards with time, eventually colouring the whole of the water homogeneously. A ball on a billiard board, on the other hand, will roll around, colliding and scattering off other balls. Transport of mass, energy or other properties in nature seem to occur predominantly in either way, called diffusive and ballistic, respectively. They constitute our intuition into the natural world and universe. However, physicists suspect that there could be other new types of transport defying our common sense. For instance, the transport of magnetic fluctuations in certain materials could occur neither diffusively nor ballistically, but somewhat intermediate. This unconventional transport is called the super-diffusion and is predicted to occur in one-dimensional quantum magnetic materials. It is also exciting that such unconventional transport could occur at room temperature in contrast with our naïve expectation that unique behaviour from quantum systems should be only observed at extremely low temperature. This could be a useful aspect for potential application such as in Spnitronics.

In this research project, I aim to provide the first clear experimental evidence for super-diffusion in quantum magnets. More specifically, I will look into crystals where magnetic ions are predominantly coupled along one direction, rather than three directions. This allows the crystals essentially behave as a collection of one-dimensional chain of magnetic ions. I will use Nuclear Magnetic Resonance (NMR) technique, akin to MRI, to evidence that the transport of magnetic fluctuations in such one-dimensional quantum chain occurs as super-diffusion. Through this research, we will be able to better understand the properties of quantum materials, which will underpin the development of new quantum technologies such as quantum sensors or computers.