Anisotropic charge dynamics in detwinned Ba(Fe 1-x Co x ) 2 As 2

We investigate the optical conductivity with light polarized along the in-plane orthorhombic a and b axes of Ba(Fe 1− x Co x ) 2 As 2 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.