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Possible High T c Superconductivity in the Ba-La-Cu-O System* J.G. Bednorz, K.A. Muller

Possible High T c Superconductivity in the Ba-La-Cu-O System* J.G. Bednorz, K.A. Muller. Theoretical Background. Introduction and Historical Context. The Experiment. Samples made by Coprecipitation with oxalates, Heating to 900 °C, 4 kbar Reheated to 900 °C

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Possible High T c Superconductivity in the Ba-La-Cu-O System* J.G. Bednorz, K.A. Muller

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  1. Possible High Tc Superconductivity in the Ba-La-Cu-O System* J.G. Bednorz, K.A. Muller Theoretical Background Introduction and Historical Context The Experiment • Samples made by • Coprecipitation with oxalates, • Heating to 900 °C, 4 kbar • Reheated to 900 °C • Superconducting grain size - 100Å • Resistivity measured using the four-point method, where two pair of electrodes are used to measure current and voltage, as shown in the adjacent figure. • The Achievement • Reported discovery of high Tc superconductivity • Resulted in Nobel Prize (1987) for authors • BCS Theory (Bardeen,Cooper,Schrieffer) • Pairing of electrons in presence of attractive electron-electron interaction • Conventional wisdom – Attractive interaction due to phonons – Strong electron-phonon interactions required – Jahn-Teller mechanism? • Previous attempts to create a high-Tc superconductor: • Metals (Hg, Pb, Al, Nb, Os, Tc) – Up to 4.46 K • Alloys (NbN, Nb3Sn) – Up to 23.3 K • Oxides (Li-Ti-O) – Up to 13.3K Jahn-Teller Distortion of an octahedral lattice. By Jahn-Teller theorem, the lattice distorts to break the degeneracy. Four point resistivity measurement • Observations • X-ray analysis shows 3 phases • K2NiF4-type perovskite • Ba concentration related cubic • Oxygen deficient perovskite • The samples exhibit high temperature metallic behavior, with increase in resistivity at low temperatures. • There is a sharp drop in resistivity at still lower temperatures – onset of superconductivity. • The drop in resistivity depends strongly on the composition as well as the way the samples were prepared (i.e., annealing temperature and pressure) Superconducting Transition Temperature Timeline • Impact • Superconductivity blasted to the forefront of public attention and became a hot topic in scientific research • Subsequent superconductivity research heavy hitters: Tony Leggett, Bob Schrieffer, Karl Mueller, Phil Anderson, Bob Laughlin, Alexei Abrikosov • Conclusions • Conventional BCS predicts Tc < 30 K – Clearly not the case for cuprates • Mechanism for electron-electron coupling – Still not clear from these results • We are still far from a theory of high temperature superconductivity Team #3: Brandon Emmerich, VatsalDwivedi, Kanuo Chen and Gilberto de la Peña *Bednorz, J. G. and Müller, K. A., Zeitschrift für Physik B, 64(2) 193 (1986)

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