Nematicity in Stripe Ordered Cuprates Probed via Resonant X-Ray Scattering

In underdoped cuprate superconductors, a rich competition occurs between superconductivity and charge density wave (CDW) order. Under debate, however, is whether rotational symmetry breaking (nematicity) also plays a central role - whether it occurs intrinsically and generically or merely as a consequence of other orders. Here we employ resonant x-ray scattering in stripeordered (La,M)$_2$CuO$_4$ to probe the relationship between electronic nematicity of the Cu $3d$ orbitals, structure of the (La,M)$_2$O$_2$ layers and CDW order. We find distinct temperature dependencies of the structure of the (La,M)$_2$O$_2$ layers and the electronic nematicity of the CuO$_2$ planes, with only the latter being enhanced by the onset of CDW order. These results suggest electronic nematicity is an order parameter that is distinct from a purely structural order parameter in underdoped cuprates.