Research: Spontaneous Formation of Exceptional Points at the Onset of Magnetism

Researchers at the University of Würzburg and TU Dresden have revealed a profound interplay between the ubiquitous phenomenon of spontaneous symmetry breaking and topological phases unique to dissipative systems. Generally speaking, in the realm of topological matter symmetry protected surface states are intuitively expected to perish when a system undergoes an ordering transition spontaneously breaking the underlying symmetry. Quite remarkably, this situation is drastically changed for dissipative symmetry breaking perturbations which may instead stabilize symmetry protected surface states, thus promoting them to full topological stability. Along these lines, studying the fate of time-reversal symmetry protected surface states of a three-dimensional topological insulator at the onset of ferromagnetism, L. Crippa et al. have now demonstrated and exemplified how magnetic fluctuations may induce topologically stable surface exceptional points, the dissipative counterpart of Weyl semimetals.

L. Crippa, G. Sangiovanni, J. C. Budich,
Spontaneous Formation of Exceptional Points at the Onset of Magnetism,
Phys. Rev. Lett. 130, 186403 (2023) (arXiv)