What it is
The authors experimentally realize a non-Hermitian phase transition in a bulk condensed-matter system, a regime where the dynamical behavior rather than steady-state properties changes qualitatively at a critical exceptional point. Optically exciting charge carriers in ferromagnetic europium monoxide, they observe a temperature-dependent change in the relaxation dynamics that appears in time-resolved reflection data as a shift from biexponential real decay to single-exponential complex decay. An accompanying theory reproduces this behavior.
Why it matters
Non-Hermitian phase transitions had largely been the domain of engineered, driven systems rather than ordinary bulk materials. Observing one intrinsically in a bulk solid, in interplay with the material's own ferromagnetic ordering and matched to theory, suggests such transitions may emerge generically in condensed matter rather than only in specially designed setups.
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Filed underQuantum Mechanics and Non-Hermitian Physics, Thermal properties of materials, Quantum, superfluid, helium dynamics