# Nematicity in the superconducting mixed state of strain detwinned underdoped $\text{Ba}(\text{Fe}_{1-x}\text{Co}_x)_2\text{As}_2$

## TL;DR

This study investigates nematic effects in the superconducting phase of underdoped Ba(Fe,Co)2As2, revealing strong in-plane resistivity anisotropy influenced by strain and nematicity, but limited impact on superconducting stiffness anisotropy.

## Contribution

It demonstrates how strain-induced nematicity affects resistivity and superconducting properties in underdoped iron pnictides, providing new insights into nematic-superconductivity interplay.

## Key findings

- Strong in-plane resistivity anisotropy linked to nematicity.
- Nematic effects significantly influence conduction but less so on superconducting stiffness.
- Strain tuning reveals intrinsic nematicity effects in detwinned samples.

## Abstract

Evidence of nematic effects in the mixed superconducting phase of slightly underdoped $\text{Ba}(\text{Fe}_{1-x}\text{Co}_x)_2\text{As}_2$ 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 {\em 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.