| high-temperature superconductors | |
|---|---|
| Name | High-temperature superconductors |
| Type | Superconductor |
| Discovered | 1986 |
| Discoverer | Georg Bednorz and K. A. Müller and J. Georg Bednorz |
| Critical temperature | Variable (up to >100 K) |
| Composition | Copper oxides, iron pnictides, others |
high-temperature superconductors
High-temperature superconductors are classes of materials that exhibit superconductivity at temperatures much higher than those of conventional low-temperature superconductors, often above the boiling point of liquid nitrogen. They are central to Quantum physics because they manifest macroscopic quantum coherence, unconventional pairing symmetries and strong electronic correlations that challenge and extend microscopic theories such as the BCS theory.
High-temperature superconductors (HTS) include families of copper-oxide cuprate superconductors and iron-based superconductors such as pnictide and chalcogenide compounds. The discovery of superconductivity above 30 K in La2−xBaxCuO4 and later above 90 K in YBa2Cu3O7 (YBCO) transformed condensed matter physics and spurred intense efforts at institutions like IBM research labs, Bell Labs, Los Alamos National Laboratory, and universities including University of Zurich and University of Cambridge. HTS probe quantum many-body phenomena including Mott insulator behavior, antiferromagnetism, pseudogap phases, and non-Fermi liquid behavior, making them paradigmatic systems for studying electron correlation, quantum criticality, and emergent order.
The canonical HTS materials are layered oxides with perovskite-related structures. Prominent examples include La2−xSrxCuO4 (LSCO), Bi2Sr2CaCu2O8+δ (Bi-2212), YBCO, and HgBa2Ca2Cu3O8+δ (Hg-1223). Common features are copper-oxide (CuO2) planes separated by charge-reservoir layers; superconductivity is strongly anisotropic and primarily two-dimensional. Iron-based superconductors were discovered in the late 2000s (e.g., LaOFeAs), featuring FeAs or FeSe layers and distinct crystal symmetries (Pnma, P4/nmm). Other HTS families include bismuthates, ruthenates (e.g., Sr2RuO4 debated), and hydrogen-rich superconductors under high pressure such as metallic hydrogen analogs investigated at facilities like Lawrence Livermore National Laboratory and Max Planck Institute for Solid State Research.
HTS challenge the conventional BCS theory because the pairing glue and symmetry are often unconventional. In cuprates, the consensus favors d-wave pairing symmetry mediated by antiferromagnetic spin fluctuations; key theoretical frameworks include the Hubbard model, the t-J model, and resonating valence bond (RVB) theory as proposed by Philip W. Anderson. For iron-based superconductors, multi-band models and orbital fluctuations, as well as spin-density-wave correlations, are central. Theories invoke concepts from quantum field theory and renormalization such as quantum critical points, gauge fields, and emergent topology in some proposals. Advanced numerical methods—density matrix renormalization group (DMRG), dynamical mean field theory (DMFT), and quantum Monte Carlo—are routinely applied at centers like Princeton University, MIT, and ETH Zurich to compute spectral functions and phase diagrams.
Key experimental probes include angle-resolved photoemission spectroscopy (ARPES) performed at synchrotrons (e.g., European Synchrotron Radiation Facility), scanning tunneling microscopy/spectroscopy (STM/STS) pioneered in groups at IBM Zurich Research Laboratory and University of Geneva, neutron scattering at reactors such as Institut Laue–Langevin, nuclear magnetic resonance (NMR), muon spin rotation (µSR), and transport measurements under high magnetic fields at facilities like the National High Magnetic Field Laboratory. Landmark discoveries include the 1986 cuprate superconductivity by J. G. Bednorz and K. A. Müller, the determination of d-wave symmetry via phase-sensitive experiments by groups including C. C. Tsuei and John R. Kirtley, and the 2008 discovery of iron pnictide superconductors by H. Hosono's group. High-pressure experiments revealing record Tc in hydrides involved teams led by Drozdov (Eremets) at Max Planck Institute for Chemistry and Max Planck Institute for Solid State Research collaborations.
HTS have enabled practical devices such as superconducting magnets, prototype maglev systems, fault current limiters, SQUID magnetometers, and cables cooled by liquid nitrogen that reduce cryogenic costs. Companies and labs—American Superconductor Corporation, Sumitomo Electric Industries, and national labs—develop wires from YBCO and Bi-2212. Challenges include grain-boundary weak links, vortex pinning and flux creep, materials synthesis scalability, and reproducible high critical current density (Jc). Integration into quantum technologies requires low dissipation and coherence control for qubits; HTS are less used for superconducting qubits compared with low-Tc materials like aluminium and niobium but remain of interest for hybrid devices and topological proposals.
Major open questions concern the exact pairing mechanism in various HTS families, the nature of the pseudogap in cuprates, and the role of charge-density-wave order and nematicity. Active research areas include engineered heterostructures at institutions such as Columbia University and Stanford University, interface superconductivity (e.g., LaAlO3/SrTiO3), angle-resolved experiments resolving competing orders, and machine-learning approaches to materials discovery. Efforts to achieve room-temperature superconductivity focus on hydride systems under extreme pressure, chemical doping strategies, and strain or intercalation engineering. Cross-disciplinary collaborations among condensed matter theorists, materials scientists, and applied physicists at organizations like Argonne National Laboratory and the CERN continue to drive progress toward both fundamental understanding and technological deployment.
Category:Superconductors Category:Condensed matter physics