Using the exactly solvable model of quantum spin liquids, they demonstrated that higher-order two-dimensional non-linear susceptibilities would show sharp signatures of Majorana fermions, elusive particles that exist in quantum spin liquids, in contrast to conventional spectroscopic methods. This work is recently published in Physical Review Letters.

The link to the paper is as follows.

https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.124.117205