Nematic fluctuations in iron-based superconductors studied by resistivity change under uniaxial pressure

Abstract

Antiferromagnetic, nematic and superconducting phases have been widely found in iron-based superconductors. The study on their relationships is thus crucial for understanding the low-energy physics and high-temperature superconductivity. The so-called nematic phase represents a spontaneous in-plane rotational symmetry breaking of the electronic states, which results in strong in-plane anisotropic properties. We have developed a uniaxial pressure device, which enables us to obtain nematic susceptibility by studying the resistivity change under uniaxial pressure at low temperature. In this paper, we brief two of our recent researches on nematic fluctuations in iron-based superconductors. The first research shows the presence of a nematic quantum critical point in BaFe2-xNixAs2, which exhibits several characteristics, including the zero mean-field nematic transition temperature x=0.11, broad hump feature in the nematic susceptibility in overdoped samples, strongest nematic susceptibility along the (100) direction at x=0.11, and the divergence of zero-temperature nematic susceptibility at x=0.11 for uniaxial pressure along both the (110) and (100) directions. We further study the nematic susceptibility in many other iron-based superconductors and find that the ordered moment at zero temperature linearly scales with nematic Curie constant, which is obtained from the Curie-Weiss-like temperature dependence of nematic susceptibility in these materials. Accordingly, we propose a universal phase diagram for iron-based superconductors, where superconductivity is achieved by suppressing the long-range antiferromagnetic order in a hypothetical parent compound though the enhancement of nematic fluctuations by doping, including both carrier doping and isovalent doping. Our results suggest that nematic fluctuations play a very important role in both the antiferromagnetism and superconductivity in iron-based superconductors.