Extended nematic quantum criticality in FeSe_xTe_1-x

Unconventional superconductivity is often accompanied by non-Fermi liquid behavior, which arises near a quantum critical point — a point where an electronic ordered phase is terminated at absolute zero by non-thermal parameters [1]. Quantum criticality may extend over a wide region of parameter space, yet the materials exhibiting such behavior are limited [2]. Here, we report evidence for extended quantum criticality in strongly correlated iron-based superconductors FeSe_xTe_1−x, characterized by temperature-linear resistivity and logarithmic divergence of thermoelectricity over a wide substitution range of 0.08 ≤ x ≤ 0.45 situated between antiferromagnetic and nematic quantum critical points. Notably, the Seebeck coefficient peaks sharply at the nematic quantum critical point x = 0.45, suggesting a dominant role of nematic fluctuations in the NFL transport. Our results reveal the pervasive nature of the extended quantum criticality and could open new avenues for exploring novel superconducting phases arising from strong quantum fluctuations.