No Nematicity at the Onset Temperature of the Pseudogap Phase in the Cuprate Superconductor YBa2Cu3Oy

Electronic nematicity is the spontaneous loss of rotational symmetry in a metal, without breaking translational symmetry. In the cuprate superconductors, there is experimental evidence for nematicity, but its origin remains unclear. Here we investigate the onset of nematicity in the transport of charge by means of electric and thermoelectric measurements in underdoped YBa2Cu3Oy, performed by passing the current (electrical or thermal) first along the a axis then the b axis of the orthorhombic structure in the same crystal, with a hole doping p = 0.12. Upon cooling, we observe no additional in-plane anisotropy-beyond the background anisotropy due to the CuO chains-in either the resistivity rho or the Seebeck coefficient S as the temperature T* for the onset of the pseudogap phase is crossed. We conclude that the pseudogap phase of cuprates is not nematic. However, at temperatures much lower than T*, a strong additional anisotropy is observed, most clearly in the Peltier coefficient alpha = S/rho. We interpret it as nematicity associated with the development of charge order.