Unconventional Dynamical Scaling close to a Nematic Quantum Critical Point*

In the vicinity of quantum critical points, the complex interplay between electronic and structural order can lead to a vast range of highly unconventional phases. Of particular interest is the electronic nematic order, with its predicted long-range interactions mediated through the lattices shear modes. Here, we report an unusual scaling relation of the magnetoresistivity in the iron-based superconductor FeSe_0.89S_0.11 when tuned to its nematic quantum critical point under hydrostatic pressure. We observe a remarkably sharp crossing over two decades in temperature, which fulfills a power-law scaling relation with diverging critical exponents at low temperatures, in stark contrast to the usual fixed exponent ansatz. We discuss our findings in the context of disconnected static and dynamic quantum fluctuations, a coupling between electronic and phononic modes, and topological changes of the Fermi surface. These lead to the emergence of an atypical non-zero energy scale at the quantum critical point which strongly affects superconductivity.