| superconductivity | |
|---|---|
| Name | Superconductivity |
| Caption | Flux lines in a type II superconductor (schematic) |
| Discovery | 1911 |
| Discovered by | Heike Kamerlingh Onnes |
| Field | Condensed matter physics |
| Key people | John Bardeen, Leon Cooper, Robert Schrieffer, Vitaly Ginzburg, Lev Landau |
superconductivity
Superconductivity is a quantum phenomenon in which certain materials exhibit exactly zero electrical resistance and expel magnetic fields below a characteristic critical temperature. It is central to Quantum Physics and Condensed matter physics because it manifests macroscopic quantum coherence and enables applications ranging from precision measurement to national infrastructure.
Superconductivity was first observed in mercury by Heike Kamerlingh Onnes in 1911 while studying electrical resistance at cryogenic temperatures at the Leiden University laboratory. Early experimental milestones included the identification of the critical temperature, critical field and critical current, and the discovery of the Meissner effect by Walther Meissner and Robert Ochsenfeld in 1933. The development of low-temperature techniques such as the use of liquid helium by Onnes and the later commercialization of cryocoolers by companies like Cryomech and Sumitomo Heavy Industries enabled wider research. Theoretical progress grew slowly until mid-20th century advances culminating in the microscopic BCS theory and later phenomenological models by Lev Landau and Vitaly Ginzburg. National research programs at institutions like Bell Labs, Argonne National Laboratory, IBM Research, Los Alamos National Laboratory, and universities including Harvard University and University of Cambridge accelerated both basic science and technological transfer.
At the quantum level, superconductivity arises from paired electrons forming bound states called Cooper pairs, which condense into a collective ground state described by a macroscopic wavefunction. The pairing mechanism in conventional superconductors involves electron–phonon interactions as formulated in BCS theory by John Bardeen, Leon Cooper, and Robert Schrieffer. The condensate exhibits long-range phase coherence and a finite energy gap in the single-particle excitation spectrum, observable via tunneling experiments pioneered by Ivar Giaever and spectroscopic methods such as ARPES at facilities like Stanford Synchrotron Radiation Lightsource and SLAC National Accelerator Laboratory. Quantum field theory techniques, Ginzburg–Landau theory, and the concept of spontaneous symmetry breaking link superconductivity to broader paradigms in Quantum field theory and the Standard Model context through analogies with the Higgs mechanism.
Superconductors are classified as conventional (phonon-mediated) or unconventional (non-phononic pairing). Notable classes include elemental superconductors (e.g., lead, niobium), intermetallic compounds (e.g., NbTi, Nb3Sn), cuprate high-temperature superconductors such as YBCO discovered by the Bednorz and Müller group, and iron-based superconductors like the pnictides discovered in laboratories at University of Tokyo and elsewhere. Other families encompass heavy-fermion systems (e.g., CeCu2Si2), organic superconductors (e.g., BEDT-TTF salts), and recently discovered hydride superconductors under high pressure such as H3S and LaH10 investigated at facilities like Max Planck Institute for Chemistry and high-pressure laboratories. Materials research is conducted by corporations, national labs, and university centers including MIT, University of Illinois Urbana-Champaign, and Oak Ridge National Laboratory.
BCS theory provides a microscopic description of superconductivity via an instability of the Fermi surface to Cooper pairing, predicting the superconducting energy gap and critical temperature. Extensions include Eliashberg theory for strong-coupling superconductors and Gor'kov's Green function formalism linking BCS to Ginzburg–Landau theory. For unconventional superconductors, models invoking spin fluctuations, charge order, and topological pairing have been developed by theorists at institutions such as Princeton University and Stanford University. Theoretical tools include density functional theory for superconductors, renormalization group methods, and numerical techniques like quantum Monte Carlo and dynamical mean field theory applied by research groups worldwide.
Key manifestations of superconductivity include the Meissner effect, which distinguishes a superconductor from a perfect conductor by active magnetic field expulsion, and flux quantization in units of the flux quantum φ0 = h/2e observed in superconducting rings. The Josephson effect—direct current and alternating current tunneling across weak links—gives rise to devices such as the SQUID (Superconducting Quantum Interference Device) developed at IBM and used in biomagnetism and geophysics. Vortex physics in type II superconductors underlies applications in high-field magnets, described by models from Abrikosov and experimental visualization by scanning tunneling microscopy groups.
Characterization techniques include electrical transport measurements (four-point probe), magnetic susceptibility via SQUID magnetometry, heat capacity, tunneling spectroscopy (including scanning tunneling microscopy), and neutron scattering at user facilities like the Spallation Neutron Source. High-pressure synthesis and diamond anvil cell experiments are essential for hydride superconductors. Cryogenic infrastructure—liquid helium, dilution refrigerators, and closed-cycle cryocoolers—supports low-temperature experiments. Standards and collaborations involve agencies such as National Institute of Standards and Technology and multinational consortia in superconducting materials and instrument development.
Superconductors enable powerful electromagnets for magnetic resonance imaging (MRI) machines produced by firms such as GE Healthcare and Siemens Healthineers, high-field magnets for particle accelerators at CERN and Fermilab, lossless power transmission experiments, and fault-current limiters for resilient grids overseen by utilities and national laboratories. Emerging quantum technologies exploit superconducting circuits in superconducting qubits used by companies and research centers including Yale University, Google's quantum computing team, and Rigetti Computing. The stability and strategic value of superconducting infrastructure intersect with national priorities for energy security, advanced manufacturing, and defense, motivating sustained public and private investment.
Category:Condensed matter physics Category:Quantum mechanics