While conventional superconductors, discovered over a century ago, required cooling to extremely low temperatures, these new materials, primarily copper oxides known as cuprates, exhibited superconductivity at significantly higher temperatures achievable with liquid nitrogen. This opened the door to potentially revolutionary technologies, from lossless power transmission to ultra-fast computing. Yet, despite over three decades of intense research, the underlying mechanism driving this phenomenon remains one of the most profound unsolved mysteries in condensed matter physics. The initial excitement has tempered into a persistent, frustrating enigma, demanding a re-evaluation of fundamental principles.
The breakthrough came from researchers at IBM’s Zurich lab, led by Georg Bednorz and K. Alex Müller, who in 1986 published their findings on lanthanum barium copper oxide. This discovery, for which they were awarded the Nobel Prize in Physics in 1987, shattered the established understanding of superconductivity, rooted in the Bardeen-Cooper-Schrieffer (BCS) theory developed in 1957 by John Bardeen, Leon Cooper, and John Robert Schrieffer. BCS theory explained superconductivity as arising from the formation of Cooper pairs, pairs of electrons bound together by vibrations in the crystal lattice, known as phonons. However, the strength of the electron-phonon interaction in cuprates was deemed insufficient to explain the observed high transition temperatures. This immediately signaled that a fundamentally different mechanism was at play, one that continues to elude physicists today.
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