New quantum state discovered

A predicted quantum state of matter has now been detected by an international team of scientists.

Quantum spin liquid causes electrons to break into pieces and was first predicted almost 80 years ago by Ettore Majorana. The first signatures of these particles, called Majorana fermions, were measured in a two dimensional material – alpha-ruthenium chloride (?-RuCl₃).

Dr Johannes Knolle, the study’s co-author from Cambridge University, said: “This is a new addition to a short list of known quantum states of matter.”

The team say their results match with the Kitaev model – a theoretical model for quantum spin liquid. QSL are states of matter thought to be present in some magnetic materials.

In materials containing a spin liquid state, when cooled to absolute zero, the electrons do not align but instead form an entangled soup. This differs from a typical magnetic material where all the electrons would arrange themselves to face the same direction.

Dr Dmitry Kovrizhin, another co-author from Cambridge said: “Until recently, we didn’t even know what the experimental fingerprints of a quantum spin liquid would look like. One thing we’ve done in previous work is to ask, if I were performing experiments on a possible quantum spin liquid, what would I observe?”

Neutron scattering techniques were used to look for evidence of fractionalisation (electron splitting) by the scientists testing the magnetic properties of ?-RuCl₃. The team observed a pattern of ripples consistent with earlier predictions made by Dr Knolle in 2014.

Dr Kovrizhin said: “It’s an important step for our understanding of quantum matter. It’s fun to have another new quantum state that we’ve never seen before – it presents us with new possibilities to try new things.”

It is thought the Majorana fermion could be used as ‘building blocks’ for quantum computing.

The study, a collaboration between researchers at Cambridge University and Oak Ridge National Laboratory in Tennessee, was published in Nature Materials.