Electronic nematicity revealed by torque magnetometry in EuFe2(As1−xPx)2

Electronic nematics, an electron orientational order which breaks the underlying rotational symmetry, were observed in iron pnictide superconductors several years after their discovery. However, the universality of the doping dependence of this phase and its relation to other symmetry-breaking orders (such as superconductivity) in distinct families of iron pnictides remain outstanding questions. Here we use torque magnetometry as a probe to study the rotational symmetry breaking in EuFe2(As1-xPx)(2) without introducing external pressure. The nematic phase is found to proliferate well above the structural transition and to persist into the superconducting regime at optimal doping, after which it becomes absent or very weak, in sharp contrast to the behavior observed in BaFe2(As1-xPx)(2). These measurements suggest a putative quantum nematic transition near optimal doping under the superconducting dome.