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

2. Josephson Effect (see also hand-out) 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: 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. 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...) JJ’s essential in Superconducting Interference Devices

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

5. Possible High Tc superconductivity in the Ba – La – Cu – O system resistivity (  cm)  Temperature ( K )  35 K 10 K 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. High-T c Superconductivity Alex Müller and Georg Bednorz Paul Chu 164 K

7. 93 K ! 77 K liquid nitrogen

8. 1910 1930 1950197019751980 1990 1985 2000 1995 2005 Hg Pb Nb NbO NbN V 3 Sn NbAlSi Nb 3 Sn Ba(Pb,Bi)O 3 organic materials NbGe 3 Ba(K,Bi)O 3 Doped buckyballs A 3 C 60 MgB 2 39K Liquid N 2 Liquid He 0 - 10 - 70 - 30 - 20 - 120 - 60 - 50 - 40 - 110 - 90 - 100 - 80 - 130 - 140 - 150 - Temperature (K) conventional superconductors (La,Ba)CuO Bednorz and Muller TlBaCaCuO Bi 2 Sr 2 Ca 2 Cu 3 O x HgBaCaCuO pressure ~ 155K “High temperature” “cuprate” superconductors YBa 2 Cu 3 O 7-d pressure

9. The crystal structures of High-Tc superconducting materials all have copper- oxide CuO 2 layers Is a room-temperature superconductor out there waiting to be discovered ?? Have we reached the maximum possible T c in this class of materials? We are still not sure exactly why this is important!

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 (La 2 CuO 4, YBa 2 Cu 3 O 6, Bi 2 CaSr 2 LnO 8 ) 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) H c1 & H c2 (parallel to c-axis): 1 T & 120T : ~1400 Å  : 10-30 Å in ab plane ~ 3 Å in perpendicular plane Jc: ~10 4 amp./cm 2 (bulk) 10 6 -10 7 amp./cm 2 (thin films)

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

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

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-  m 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….

19. 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!!) http://superconductors.org/history.htm#resist