Research: Elastoresist­ance evidences nematic criticality under the superconducting dome of an iron-based superconductor

Unconventional superconductivity has long been considered to have intimate relationship with the ‘melting’ of other ordered states, in particular of magnetic and nematic order. Elastoresistance, the strain effect on resistance, was recently introduced to study the nematicity and has provided evidences for a nematic critical point and pertinent fluctuations in some iron-based compounds. We have used elastoresistance to study the evloution of nematicity of Co doped LaFeAsO. Our results reveal that a nematic critical point should exist under the superconducting dome, evident by the sign changing of the nematic temperature (T^nem) close to the optimal doping level. As summarized in the figure above, the amplitude of nematic susceptibility (color-coded contour plot) follows the same trend of the superconducting transition temperature T_C. Additionally, another enhancement of the nematic susceptibility is found on top of the magnetic critical one in the under-doped region. These facts can be explained by a dichotomic origin of nematicity, which may be general for all iron-based superconductors.

X. Hong, F. Caglieris, R. Kappenberger, S. Wurmehl, S. Aswartham, F. Scaravaggi, P. Lepucki, A. U. B. Wolter, H.-J. Grafe, B. Büchner, C. Hess,
Evolution of the nematic susceptibility in LaFe_1−xCo_xAsO,
Phys. Rev. Lett. 125, 067001 (2020) (arXiv)