In-plane anisotropy of charge density waves in YBa2Cu4O8 under uniaxial strain

Charge density waves (CDWs) have been observed in all underdoped cuprates, but the role of in-plane anisotropy is still missing in their microscopic description to date. In the model system YBa2Cu3O6+x (Y123), the a- and b-CDW domains have a significant in-plane anisotropy that cannot be attributed to crystal orthorhombicity. Our recent RIXS experiments on minimally disordered YBa2Cu4O8 (Y124) further revealed an asymmetric response of the CDW domains to different uniaxial strain directions. This a/b anisotropy is not present in Y123 and possibly rooted in the intrinsic nematic responses of CuO2 planes. We therefore propose a continuation RIXS experiment on Y124, to systematically measure both a- and b-CDW response under a- and b-axis uniaxial strain, respectively. We believe that the full evolution of intensity and correlation lengths of both domains will provide a better understanding of in-plane anisotropy and underlying nematicity in the yttrium-based cuprate family.