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SQUIDs (Superconducting QUantum Interference Devices)

SQUIDs (Superconducting QUantum Interference Devices). By Agnieszka Czeszumska. Talk Outline. Superconductivity Josephson Tunneling Phase of electron pairs DC SQUID Laboratory Setup Applications. Why SQUIDs?. Can detect extremely small magnetic fields For example, read out TES device.

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SQUIDs (Superconducting QUantum Interference Devices)

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  1. SQUIDs(Superconducting QUantum Interference Devices) By Agnieszka Czeszumska

  2. Talk Outline • Superconductivity • Josephson Tunneling • Phase of electron pairs • DC SQUID • Laboratory Setup • Applications

  3. Why SQUIDs? • Can detect extremely small magnetic fields • For example, read out TES device

  4. Superconductivity Below certain temperature: • Resistanceless • supercurrent • Meissner effect

  5. Superconductivity Explained – BCS Theory • Electron – lattice interaction • Cooper pairs • Energy Gap • Coherence • Flux Quantization Phonons!

  6. Superconductivity Explained – BCS Theory • Electron – lattice interaction • Cooper pairs • Energy Gap • Coherence • Flux Quantization Two coupled electrons with opposite momenta and spins Boson-like Does not scatter - resistanceless Energetically favorable in superconducting state

  7. Superconductivity Explained – BCS Theory • Electron – lattice interaction • Cooper pairs • Energy Gap • Coherence • Flux Quantization

  8. Superconductivity Explained – BCS Theory • Electron – lattice interaction • Cooper pairs • Energy Gap • Coherence • Flux Quantization Can calculate phase and amplitude at any point on the wave Coherence length One wave equation describes all Cooper pairs:

  9. Superconductivity Explained – BCS Theory • Electron – lattice interaction • Cooper pairs • Energy Gap • Coherence • Flux Quantization Magnetic flux around a closed superconducting current loop must be quantized One fluxon

  10. Josephson Tunneling • Josephson Junction – small gap between two superconductors • Cooper pairs can tunnel • Critical current supercurrent Phase difference across the junction

  11. Change in Phase Due to: • Current • Magnetic field • Josephson Junctions = P

  12. DC SQUID • Superconductor • Current loop • Two Josephson Junctions

  13. How it works Voltage change Phase change due to external magnetic field Current flow Due to B field Due to junctions Must be quantized

  14. How it works

  15. Aiding Detection • Gradiometer, Magnetometer, Voltometer

  16. Lab Setup – Two Stage

  17. Characterisation • I V curve • V Phi curve

  18. Other Applications Beyond X-Ray Astrophysics... • Medical imaging (MEG) • Geology

  19. References • A.C. Rose-Innes and E.H. Rhoderick, „Introduction to Superconductivity”, 2nd ed., 1978 • Kittel, Charles, „Introduction to Solid State Physics”, 6th ed., 1986 • Clarke, John, „SQUIDs”, Scientific American (August 1994) • STAR Cryoelectronics, Manual • SQUID Magnetometry, http://www.cmp.liv.ac.uk/frink/thesis/thesis/node41.html • http://hyperphysics.phy-astr.gsu.edu/hbase/solids/supcon.html#c1 • Thank you Mark and Prof. McCammon for answering my random questions • Special thanks to Emily Barrentine for help and resources

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