Anisotropic charge dynamics in detwinned Ba(Fe1-xCox)2As2

We investigate the optical conductivity with light polarized along the in-plane orthorhombic a and b axes of Ba(Fe1−xCox)2As2 for x=0 and 2.5% under uniaxial pressure across their structural and magnetic transitions. The charge dynamics at low frequencies and temperatures on these detwinned, single-domain samples reveals an enhancement of both the scattering rate and Drude weight of the charge carriers along the antiferromagnetic a-axis with respect to the ferromagnetic b-axis. Our findings also allow us to estimate the dichroism, which extends to high frequencies and temperatures. These results reveal a nematic susceptibility as well as the electronic nature of the structural transition.