Long-awaited discovery on the shores of Lake Zurich (Brief Review)

The discovery of high-temperature superconductivity in copper oxides by Karl Alexander Müller and Johannes Georg Bednorz in 1986 marked a turning point in condensed matter physics and opened a new era in the science of superconducting materials. This article retraces the scientific path that led to the breakthrough achieved at the IBM laboratory near Lake Zurich, placing it within the broader historical and theoretical context of the long search for superconductors with higher critical temperatures. We discuss the limitations imposed by the conventional BCS framework, the role of lattice stability, and the emergence of alternative ideas based on low-dimensional systems and non-phononic pairing mechanisms, as proposed by William Little and Vitaly Ginzburg. Particular attention is devoted to the discovery of superconductivity in oxide compounds and organic conductors during the 1970s and early 1980s, developments that prepared the ground for the identification of superconductivity in the perovskite compound La2–xBaxCuO4–δ at 35 K. The article also highlights the unusual circumstances of this discovery: it was achieved by a small team with limited resources, using simple ceramic materials, yet it revolutionized the field and rapidly led to the discovery of cuprate superconductors with ever higher transition temperatures. Finally, we discuss the enduring mystery of the microscopic mechanism of high-temperature superconductivity in cuprates and the continuing theoretical challenges posed by these remarkable materials.