| YBa2Cu3O7 | |
|---|---|
| Name | YBa2Cu3O7 |
| Caption | Crystallographic motif of the orthorhombic phase |
| Formula | YBa2Cu3O7 |
| Othernames | YBCO, Y-123 |
| Category | High-temperature superconductor |
YBa2Cu3O7
YBa2Cu3O7 (commonly abbreviated YBCO or Y‑123) is a ceramic copper oxide compound known for its high critical temperature superconductivity in the orthorhombic oxygen-stoichiometric phase. It is a prototype high-temperature superconductor that has played a central role in experimental and theoretical developments in Condensed matter physics and the study of quantum coherent phenomena relevant to quantum information science.
YBa2Cu3O7 crystallizes in a layered perovskite-derived structure containing CuO2 planes, chains of CuO linear units, and planes of yttrium and barium that act as charge reservoirs. The ideal stoichiometry is often written YBa2Cu3O7−δ to reflect oxygen deficiency (δ), which controls the electronic doping and the transition between orthorhombic and tetragonal phases. Key structural motifs include the square-planar copper coordination in the CuO2 plane and the chain copper sites that modulate carrier concentration; these features are directly related to superconducting properties and anisotropic transport measured along the crystallographic a, b, and c axes. The compound was first discovered in 1987 at University of Houston-affiliated labs and by teams including researchers at Bell Labs and IBM, rapidly catalyzing the field of high-Tc superconductivity.
YBa2Cu3O7 exhibits superconductivity with a critical temperature (Tc) typically around 92 K for nearly oxygen-stoichiometric samples, above the boiling point of liquid nitrogen, which enabled practical cryogenic experiments. Critical parameters include the coherence length (ξ) that is highly anisotropic between the CuO2 plane and interlayer directions, the London penetration depth (λ), and large upper critical fields (Hc2) and high critical current densities (Jc) in textured or engineered films and wires. Vortex physics in YBCO—pinning, flux creep, and vortex-liquid phases—has been investigated extensively at institutions such as Los Alamos National Laboratory, Argonne National Laboratory, and university research centers, with implications for dissipation and device performance in quantum circuits.
The electronic structure of YBa2Cu3O7 is governed by strongly correlated electrons in the copper-oxygen planes; the low-energy states derive mainly from hybridized Cu 3d and O 2p orbitals. Angle-resolved photoemission spectroscopy (ARPES) studies at facilities like Stanford Synchrotron Radiation Lightsource and European Synchrotron Radiation Facility resolved Fermi surface segments and pseudogap behavior. The superconducting order parameter in optimally doped YBCO is predominantly d-wave symmetry, inferred from phase-sensitive experiments by groups including C. C. Tsuei and J. R. Kirtley and from tunneling and Josephson-junction interferometry. Competing orders—charge density waves, spin fluctuations, and the pseudogap—are active research topics linked to microscopic pairing mechanisms involving antiferromagnetic exchange (J) and spin-fluctuation–mediated pairing in many-body models.
High-quality YBCO single crystals and thin films are produced using techniques such as the flux-growth method, pulsed laser deposition (PLD), molecular beam epitaxy (MBE), and metal-organic chemical vapor deposition (MOCVD). Control of oxygen content is achieved through annealing under controlled oxygen partial pressure and quenching protocols; processing steps are critical to obtain the orthorhombic superconducting phase and to optimize grain boundary connectivity. Industrial-scale wire and tape conductors exploit second-generation superconducting wire architectures with YBCO coated conductors and buffer layers developed by companies and labs including SuperPower (company) and American Superconductor.
YBa2Cu3O7 has been used in prototypes of quantum devices where high critical temperature or particular material properties are advantageous. Examples include superconducting microwave resonators, rapid single flux quantum (RSFQ) logic demonstrators, and hybrid devices coupling YBCO to spin ensembles or superconducting qubits. Research at centers such as MIT and Caltech has explored YBCO junctions and grain-boundary Josephson junctions for quantum interference devices (SQUIDs), while integration challenges with conventional low-Tc qubit architectures (e.g., transmon (qubit)) motivate hybrid approaches and studies of dissipation from quasiparticles and two-level systems.
Characterization techniques for YBCO span structural, spectroscopic, and transport methods: x-ray diffraction (XRD) and neutron scattering for crystallography and magnetic order (performed at facilities including Oak Ridge National Laboratory), ARPES and scanning tunneling microscopy (STM) for electronic structure and gap mapping, nuclear magnetic resonance (NMR) and muon spin rotation (μSR) for local magnetism and penetration depth, and magneto-transport and magnetization for critical fields and vortex dynamics. Advanced nanofabrication combined with low-temperature cryogenics and microwave spectroscopy allow measurements of coherence times and loss mechanisms relevant to quantum device performance.
YBCO is a paradigmatic system for theoretical studies in quantum many-body physics. Models applied include the single-band and three-band Hubbard models, the t–J model, and renormalization-group and dynamical mean-field theory (DMFT) approaches to capture correlation effects. The interplay of superconductivity with competing orders has been studied using numerical techniques such as quantum Monte Carlo and density matrix renormalization group (DMRG). Insights gained from YBCO inform broader topics in strongly correlated electron systems, quantum criticality, and the emergence of superconductivity from doped Mott insulators, with active theoretical contributions from groups at Princeton University, University of Cambridge, and Harvard University.
Category:High-temperature superconductors Category:Copper oxide superconductors