YBa$$_$$Cu$$_4$$4O$$_8$$8

High temperature superconductivity in copper oxides remains a challenge more than 25 years after their discovery by Bednorz and Mueller (Zeitschrift fur Physik B 64:189, 1986, [1]). High quality single crystals in the field of iron-pnictides were available within months after their discovery, whereas it took almost 20 years until advances in crystal quality and measurement techniques in high magnetic field lead to the first observation of quantum oscillations in the cuprates (Doiron-Leyraud et al., Nature 447:565, 2007, [2]).