It was noted that single crystals of this material could be de-twinned by the simultaneous application of heat and uni-axial stress. However, this did not work for thin films as they became heavily twinned due to strain from the underlying substrate as well as from the orthorhombic unit cell. Such a lack of control over twinning made it difficult to determine the role played by twins in governing transport properties. A technique was presented here for de-twinning thin films. This was achieved by suspending a portion of the film above the substrate. The suspended material was no longer influenced by the confining effects of the substrate, and this permitted it to de-twin under the application of a uni-axial stress which was imposed by annealing. By using this technique, it was possible to produce high-quality de-twinned regions.

Detwinning YBa2Cu3O7–δ Thin Films. J.Nam, R.A.Hughes, A.Dabkowski, J.S.Preston: Applied Physics Letters, 2003, 82[21], 3728-30