Nematicity in the superconducting mixed state of strain detwinned underdoped Ba( Fe1−xCox)2As2

Abstract

Evidence of nematic effects in the mixed superconducting phase of slightly underdoped Ba(Fe1−xCox)2As2 is reported. We have found strong in-plane resistivity anisotropy for crystals in different strain conditions. For these compositions, there is no magnetic long range order, so the description may be ascribed to the interplay between the superconducting and nematic order parameters. A piezoelectric-based apparatus is used to apply tensile or compressive strain to tune nematic domain orientation in order to examine intrinsic nematicity. Measurements are done under a rotating magnetic field and the analysis of the angular dependence of physical quantities identifies the cases in which the sample is detwinned. Furthermore, the angular dependence of the data allows us to evaluate the effects of nematicity on the in-plane superconductor stiffness. Our results show that although nematicity contributes in a decisive way in the conduction properties, its contributions to the anisotropy properties of the stiffness of the superconducting order parameter is not as significant in these samples.

Vortices in a Ginzburg Landau Theory of Superconductors with Nematic Order

“…[51,52] (for a case in which the nematic parameter is complex see [53]). Superconducting-nematic coupling of this kind was also considered in [37] in the study of strain detwined mixed states [54]. In a more general setting additional terms incorporating strain, stress, and their couplings to the order parameters can also be included [55][56][57][58][59].…”

“…Growing experimental evidence points towards this connection, where competition and cooperation are suggested in iron based superconductors BaFeAs [33,34] and FeSe [35], respectively [36]. However, the character of this coupling is still matter of debate [37,38].…”