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| cuprate superconductors | |
|---|---|
| Name | Cuprate superconductors |
| Type | Ceramic oxide superconductors |
| Discovered | 1986 |
| Discoverer | Bednorz and Müller |
| Tc record | ~135 K (ambient pressure) Hg-based cuprates |
cuprate superconductors are a class of high-temperature superconductors based on copper oxide planes that show superconductivity at temperatures far above those of conventional elemental superconductors. They exhibit layered perovskite-derived structures, strong electron correlations, and a rich phase diagram with antiferromagnetism, pseudogap phases, and unconventional d-wave pairing. Research on cuprates bridges experimental work at facilities such as Bell Labs, IBM Research, Los Alamos National Laboratory, and CERN with theoretical efforts from groups associated with Stanford University, Princeton University, and Massachusetts Institute of Technology.
Cuprates comprise families like the lanthanum, yttrium–barium–copper oxide, and bismuth, together with mercury- and thallium-based compounds studied at University of Zurich and Max Planck Society laboratories. Early breakthroughs involved researchers at IBM Zurich Research Laboratory and teams led by J. Georg Bednorz and K. Alex Müller, whose work led to the Nobel Prize in Physics. Major experimental platforms include beamlines at Brookhaven National Laboratory, Argonne National Laboratory, and synchrotrons like European Synchrotron Radiation Facility for spectroscopy and scattering. The cuprates connect to topics investigated at Harvard University, Columbia University, and University of Cambridge through cross-disciplinary efforts in condensed matter physics.
The defining structural motif is the copper–oxygen plane found in perovskite-based unit cells such as those of YBCO and LSCO, often interleaved with charge reservoir layers incorporating elements like bismuth, thallium, mercury, and calcium. Variations include single-, double-, and triple-layer cuprates studied by groups at University of Tokyo and University of California, Berkeley; examples include Bi-2201, Bi-2212, and Bi-2223 families characterized by differing CuO2 plane counts. Crystal chemistry investigations at institutions such as National Institute of Standards and Technology and Oak Ridge National Laboratory employ diffraction methods refined by researchers from University of Oxford and ETH Zurich to determine lattice parameters, oxygen stoichiometry, and ordering phenomena.
The phase diagram versus doping and temperature shows antiferromagnetic order in parent compounds like La_2CuO_4 and superconductivity upon hole or electron doping by substitutions such as Sr for La or Ce for Nd, work developed in laboratories at University of Tokyo and Tsinghua University. Angle-resolved photoemission spectroscopy (ARPES) studies at SLAC National Accelerator Laboratory and Stanford Synchrotron Radiation Lightsource revealed Fermi surface arcs and nodal quasiparticles discussed by researchers from Rutgers University and University of Illinois Urbana-Champaign. The pseudogap regime, a topic of debate involving groups at Columbia University and University of British Columbia, juxtaposes superconducting fluctuations with competing orders such as charge-density waves observed by teams at Max Planck Institute for Solid State Research and Diamond Light Source.
The leading interpretation invokes unconventional pairing symmetry—predominantly d-wave—elucidated via phase-sensitive experiments by investigators at Ohio State University and University of Pennsylvania. Competing theoretical frameworks include spin-fluctuation-mediated pairing championed by theorists at Princeton University and University of Cincinnati, resonating-valence-bond (RVB) ideas associated with Anderson, P. W. and pursued at Bell Labs affiliations, and proposals involving quantum criticality studied at Perimeter Institute and Institute for Advanced Study. Numerical methods developed at Los Alamos National Laboratory and Institute Max Planck—including dynamical mean-field theory and density-matrix renormalization group—address strong-correlation effects derived from Hubbard and t-J models investigated by groups at University of California, Santa Barbara and Cornell University.
Key experimental tools include ARPES at SLAC, scanning tunneling microscopy (STM) pioneered by researchers at IBM Research and University of California, Irvine, neutron scattering at Oak Ridge National Laboratory and Institut Laue–Langevin, and muon-spin rotation experiments at Paul Scherrer Institute. Landmark findings include the observation of d-wave gap nodes by phase-sensitive corner-junction experiments performed at University of Maryland and Stanford University, stripe and charge-order phenomena detected by x-ray scattering at Brookhaven National Laboratory, and the identification of the highest ambient-pressure Tc in mercury-based cuprates investigated by teams at University of Cambridge and University of Tokyo.
Efforts to translate cuprate superconductivity into applications involve wire and tape fabrication by companies and labs such as American Superconductor and SuperPower Inc. as well as projects at National Renewable Energy Laboratory. Applications considered include superconducting magnets for ITER, fault current limiters evaluated by General Electric collaborations, and microwave filters deployed in telecommunications by Huawei research centers. Challenges remain in grain-boundary weak links addressed by groups at University of Wisconsin–Madison and in flux creep and vortex dynamics studied at Northeastern University, which limit critical current densities and practical deployment in power grids promoted by European Commission programs.
The discovery by J. Georg Bednorz and K. Alex Müller at IBM Zurich Research Laboratory in 1986 triggered an international rush involving teams at Bell Labs, Los Alamos National Laboratory, and University of Tokyo, culminating in rapid Tc improvements from initial lanthanum cuprates to yttrium- and mercury-based compounds whose development engaged researchers at Max Planck Society and Columbia University. The rapid progress led to awards such as the Nobel Prize in Physics and spawned conferences at venues like American Physical Society meetings and workshops at Isaac Newton Institute.
Major open questions pursued at research centers including Princeton University, Perimeter Institute, and SLAC concern the origin of the pseudogap reported by teams at Columbia University and MIT, the nature of competing orders studied at Max Planck Institute and Brookhaven National Laboratory, and routes to higher Tc and improved materials processing investigated at University of California, Los Angeles and Oak Ridge National Laboratory. Ongoing directions link cuprate research with investigations of other unconventional superconductors at Rice University and with quantum materials initiatives sponsored by European Research Council and National Science Foundation.
Category:High-temperature superconductors