The Kasteleyn transition is an unconventional phase transition originally introduced in the context of classical dimer models. Unlike conventional critical phenomena, it exhibits a strikingly asymmetric behavior: the system remains frozen on one side of the transition, while on the other side defects proliferate in the form of system-spanning strings, accompanied by singular thermodynamic behavior.

In this talk, I will show that Kasteleyn physics is not restricted to classical systems but can also emerge in frustrated quantum magnets. We demonstrate this for the spin-1/2 Heisenberg model on the diamond-decorated honeycomb lattice, where a highly frustrated quantum phase built from dimer and plaquette singlets admits an exact mapping onto dimer coverings of the honeycomb lattice. A weak spatial distortion generates anisotropic dimer activities and drives the system towards a Kasteleyn transition. At finite temperature, a small and tunable density of monomer defects rounds the transition into an arbitrarily sharp crossover while preserving its characteristic signatures.

This provides, to our knowledge, the first realization of Kasteleyn physics in a frustrated quantum spin model and opens a route towards exploring this unconventional phenomenon in quantum magnetic materials. I will also briefly discuss possible generalizations to other lattice geometries and prospects for its realization in organometallic compounds.