Engineering underdoped CuO2 nanoribbons in nm-thick a-axis YBa2Cu3O7−δ films

In underdoped cuprate high-Tc superconductors, various local orders and symmetry-breaking states, in addition to superconductivity, reside in the CuO2 planes. The confinement of the CuO2 planes can therefore play a fundamental role in modifying the hierarchy between the various orders and their intertwining with superconductivity. Here we present the growth of a-axis oriented YBa2Cu3O7−δ films, spanning the whole underdoped side of the phase diagram. In these samples, the CuO2 planes are confined by the film thickness, effectively forming unit-cell-thick nanoribbons. The unidirectional confinement at the nanoscale enhances the in-plane anisotropy of the films. By x-ray diffraction and resistance vs temperature measurements, we have discovered the suppression of the orthorhombic-to-tetragonal transition at low dopings, and a very high anisotropy of the normal state resistance in the b−c plane, the latter being connected to a weak coupling between adjacent CuO2 nanoribbons. These findings show that the samples we have grown represent a novel system, different from the bulk, where future experiments can possibly shed light on the rich and mysterious physics occurring within the CuO2 planes. Published by the American Physical Society 2024