NMR Study of Single Crystal CaKFe₄As₄ Under Pulsed Uniaxial Strain

CaKFe₄As₄ is an Fe-based superconductor with a T_c ~ 34K. Previous measurements of the non-superconducting parent compound BaFe₂As₂ utilizing pulsed alternating strain fields during Larmor precession were able to improve sensitivity to nematic susceptibility by 3 orders of magnitude. We use this improved resolution to perform measurements of nematic susceptibility down into the superconducting regime, investigating the role of nematicity in the superconducting transition in these materials. The presence of two distinct ⁷⁵As sites allows for a detailed NMR study under uniaxial strain in the [110] direction under an in-plane 11.7T field.