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Brian D. Josephson The Discovery of Tunnelling Supercurrents The Nobel Prize in Physics 1973

Brian D. Josephson The Discovery of Tunnelling Supercurrents The Nobel Prize in Physics 1973. In 1962 Josephson predicted Cooper-pairs can tunnel through a weak link at zero voltage difference. Current in junction (called Josephson junction – Jj) is then equal to:.

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Brian D. Josephson The Discovery of Tunnelling Supercurrents The Nobel Prize in Physics 1973

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  1. Brian D. Josephson The Discovery of Tunnelling Supercurrents The Nobel Prize in Physics 1973

  2. In 1962 Josephsonpredicted Cooper-pairs can tunnel through a weak link at zero voltage difference. Current in junction (called Josephson junction – Jj) is then equal to: Josephson Effect(see also hand-out) Electrical current flows between two SC materials - even when they are separated by a non-SC or insulator. Electrons "tunnel" through this non-SC region, and SC current flows.

  3. JJ’s essential in Superconducting Interference Devices The SQUID may be configured as a magnetometer to detect incredibly small magnetic fields - small enough to measure the magnetic fields in living organisms. Threshold for SQUID: 10-14 T Magnetic field of heart: 10-10 T Magnetic field of brain: 10-13 T • Many uses in everyday life • Making measurements using SQUIDs (magnetic susceptibility, static nuclear susceptibility, Nuclear Magnetic resonance...) • Biomagnetism (magnetoencephalography [MEG], magnetocardiogram) • Scanning SQUID microscopy • Geophysical applications of SQUID (oil prospecting, earthquake prediction, geothermal energy surveying) • Higher Temperature SQUIDs (nondestructive testing of materials...)

  4. Georg Bednorz and Alex Muller received the Nobel Prize 1987 for discovery of the first of the copper-oxide superconductors http://www.phys.ntnu.no/brukdef/prosjekter/super/Profiles/bednmull.jpg this is how it was announced 

  5. 35 K resistivity (cm)  10 K Temperature ( K)  Possible High Tc superconductivity in the Ba – La – Cu – O system Their sample at first became more resistive as it cooled! At 35 K, when the sample was 5000 x more resistive than copper, the resistance began to fall … Only by 10 K had the resistance fallen to (possibly) zero !

  6. Paul Chu Alex Müller and Georg Bednorz High-Tc Superconductivity 164 K

  7. 93 K ! 77 K liquid nitrogen

  8. ~ 155K pressure HgBaCaCuO TlBaCaCuO “High temperature” “cuprate” superconductors Bi2Sr2Ca2Cu3Ox YBa2Cu3O7-d Liquid N2 pressure Bednorz and Muller MgB2 39K (La,Ba)CuO Ba(K,Bi)O3 Doped buckyballsA3C60 Liquid He 150 - Temperature (K) 140 - 130 - 120 - 110 - 100 - 90 - 80 - 70 - conventional superconductors 60 - 50 - 40 - 30 - NbAlSi NbGe3 V3Sn 20 - NbN Nb3Sn organic materials Pb 10 - Nb Ba(Pb,Bi)O3 Hg NbO 0 - 2005 1950 1970 1975 1980 2000 1910 1930 1985 1995 1990

  9. We are still not sure exactly why this is important! Have we reached the maximum possible Tc in this class of materials? The crystal structures of High-Tc superconducting materials all have copper-oxide CuO2 layers Is a room-temperature superconductor out there waiting to be discovered ??

  10. General features of cuprate superconductors • Cu-O sheets (with square pyramidal or octahedral coordination) • Charge reservoirs in the form of Cu-O chains or TlO(BiO) layers • Superconducting cuprates have AFM parent members (La2CuO4, YBa2Cu3O6, Bi2CaSr2LnO8) • Anisotropic properties (e.g. ab<c) • Hole superconductors (residing on oxygen):Tc is maximum at a critical hole concentration

  11. Typical values of important parameters (HTSC) • Hc1 & Hc2 (parallel to c-axis): 1 T & 120T • : ~1400 Å • : 10-30 Å in ab plane ~ 3 Å in perpendicular plane • Jc: ~104 amp./cm2 (bulk) 106-107 amp./cm2 (thin films)

  12. magnetically launched space shuttle Energy Saving:power lineselectric motorstransformers Cargo-carryingsubmarines,all-electric US Navy Medical Diagnostics:Magnetic Resonance Imaging SQUID:Brain activity Heart function 350 mph levitated Intercity trains Computing: 1000 times fastersupercomputers Information Technology: much faster, wider band communications Underground rapid transit: Heathrow to Gatwick in 10 minutes The dream - “Tomorrow’s Superconducting World”

  13. Some of these dreams are already reality… SQUID measure-ment of neuro-magnetic signals www.lanl.gov/quarterly/q_spring03/meg_helmet.shtml www.rtri.or.jp/rd/maglev/html/english/maglev_frame_E.html Japanese levitating train has superconducting magnets onboard http://www.bestofjesse.com/projects /indust/project1.html (nuclear) magnetic resonance imaging of the brain, in the field from a superconducting magnet Superconducting power cable installed in Denmark

  14. Transmission Lines • 15% of generated electricity is dissipated in transmission lines • Potential 100-fold increase in capacity • BNL Prototype: 1000 MW transported in a diameter of 40 cm Pirelli Cables & Systems

  15. Superconducting magnets An electrical current in a wire creates a magnetic field around a wire. The strength of the magnetic field increases as the current in a wire increases. Because SCs are able to carry large currents without loss of energy, they are well suited for making strong magnets. When a SC is cooled below its Tc and a magnetic field is increased around it, the magnetic field remains around the SC. If the magnetic field is increased to a critical value Hc the SC will turn normal. • Support a very high current density with a very small resistance • A magnet can be operated for days or even months at nearly constant field A typical Nb3Sn SC magnet. It produces 10.8T with a current of 146A. Bore diameter is 3.8 cm. Cross-section of multifilament Nb-Ti of 1mm overall diameter, consisting from 13255 5-mm filaments

  16. Other Uses of Superconductivity • Fault current limiters • Electric motors • Electric generators • Petaflop computers (thousand trillion floating point operations per second)

  17. Applications of Superconductivity Trade off between: Cost Saving and Cost Increase Zero resistance, no energy lost, novel uses… Need refrigeration, fabrication costs….

  18. http://superconductors.org/history.htm#resist John Bardeen, Leon Cooper and Bob Schrieffer “ B. C. S.” Nobel Prize 1972 for their theory of 1957 which explained conventional superconductors: nearly 50 years after their discovery by Kamerlingh Onnes! Who knows tomorrow B may stand for Bhavya, Bikramjit, Bhaskar,..... C may stand for (unfortunately we don’t have anybody in our class!) S may stand for Samaya, Swagnik, Surabhi, Sherya, Shamik, Sourav (there are many contenders!!)

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