Mark Potts

---

We propose using spin-qubit noise magnetometry to probe dynamical signatures of
magnetic Berezinskii-Kosterlitz-Thouless (BKT) physics. For a nitrogen-vacancy (NV) center coupled
to two-dimensional XY magnets, we predict distinctive features in the magnetic noise spectral density
in the sub-MHz to GHz frequency range. In the quasi-long-range ordered phase, the spectrum
exhibits a temperature-dependent power law characteristic of algebraic spin correlations. Above the
transition, the noise reflects the proliferation of free vortices and enables quantitative extraction
of the vortex conductivity, a key parameter of vortex transport. These results highlight NV as a
powerful spectroscopic method to resolve magnetic dynamics in the mesoscopic and low-frequency
regimes and to probe exotic magnetic phase transitions.

---

MPI-PKS Dresden
0.03
Contact: Urban Seifert