High temperature superconductivity research at the IBM thomas J. Watson and Almaden research centers

Complementing the work of Bednorz and Müller, which started the field of high temperature oxide superconductivity, the IBM Research laboratories at Yorktown Heights in Almaden have made contributions also via many outside collaborations across the full scope of this field. Materials work includes the identification, separation and structural characterization of the YBa₂Cu₃O_7–x phase, the detection of superconductivity and antiferromagnetism in La₂CuO₄, and the deposition of YBaCuO films with transition temperatures above 77 K by electron-beam deposition and plasma spraying. Characterization work includes measurement of the superconducting energy gap by far-infrared and tunneling measurements, study of Meissner and diamagnetic shielding, observation of superconducting fluctuations, correlation of Cu–O]⁺ complex concentration withT _c, and determination of valence electronic structure by photoemission. Theoretical work includes proposal of an interband scattering mechanism for superconductivity, a mean-field solution to an electron-interaction model, band-structure calculations, and a phenomenological model for lattice parameters and their influence onT _c. YBa₂CU₃O_7–d single crystals have been synthesized and shown to exhibit up to 70:1 magnetic anisotropy. In work of relevance to applications, the first thin film SQUIDs have been operated in temperatures up to 68 K, epitaxial films on SrTiO₃ have been found to sustain critical currents of more than 10⁵ A/cm² at 77 K, and coatings, superconducting above 77 K, have been deposited by plasma spraying.