Superconductivity David Kelley ECPE

What is Superconductivity?  State/Phase of matter with unique electrical, magnetic, and thermal properties.

1.The Discovery of Superconductivity 2.Properties Exhibited by Superconductive Materials 3.The BCS Theory of Superconductivity 4.High Temperature Superconductivity (HTSC) 5.The Current State of Research in HTSC 6.Development of Superconductive Technology 7.Obstacles of Superconductivity 8.Concluding Remarks

1. The Discovery of Superconductivity  Onnes – Liquefaction of Helium  Tests of electrical resistance of Hg

Nomenclature  T C – Critical Temperature  H C – Critical Magnetic Field

2. The Properties Exhibited by Superconductive Materials  Zero electrical resistance / Perfect conduction  Perfect Diamagnetism (The Meissner Effect)

Type II Superconductors  Incomplete Meissner effect

3. How Superconductivity Works (The BCS Theory)  Fritz London – ‘Giant Atom’  Cooper pairs

 Scattering – phonons  No scattering – Virtual Phonons

More on Cooper Pairs  Equal but opposite momentum/opposite spin  Momentum pair  Equalibrium – 0 net momentum  Cooper pairs are dynamic

Discrete energy  Energy to alter the momentum of an electron  Cooper pairs always have the same momentum  Energy to alter the momentum of a horde of cooper pairs

Bandgap and T C  Discrete energy required to excite an electron across bandgap (break cooper pair)  Not all materials with large bandgaps become superconductive – cooper pairs

4. High Temperature Superconductivity (HTSC)  Limits of the BCS theory  Bednorz and Muler: 30K  90K… 125K (3 groups)

If the BCS theory failed how does it work?  ‘Giant Atom’ – New Electron Mediator  Common themes amongst HTSC  Pervoskite – copper planes

5. The current state of research  Mott insulators and doping  Copper planes cause ‘resonating valence bonds’ – antiparallel electron configuration  Non copper oxide HTSC  Field effect doping superconductivity

6. Superconductive Technology  Long distance power transmission  Energy storage  Interconnects  MRI

 Maglev  Particle Accelerators

7. Obstacles  Critical temperature  Mechanical properties  Technology Inertia  No one knows how it really works?

8. Concluding remarks  Useful for magnetic and electric properties  Must balance T C and H G with other qualities  No complete theory for HTSC, perhaps we missed something with low temp SC  Field effect doping

Acknowledgements  Buckel, Werner. Superconductivity: Fundamentals and Applications. Weinheim, Germany: VCH Verlagsgesellschaft mbH,  Iovine, John. “Superconductors.” Poptronics. July November,  Iovine, John. “Superconductors.” Poptronics. July November,  Kresin, Vladimir Z. and Stuart A. Wolf. Fundamentals of Superconductivity. New York: Plenum Press,  Orlando, Terry, and Kevin A. Delin. Foundations of Applied Superconductivity. Reading, Massachusetts: Addison-Wesley Publishing Company Inc.,  Pines, David, and Ulam Scholar. Understanding High Temperature Superconductivity: Progress and Prospects. Center for Nonlinear Studies at Los Alamost National Laboratory and Physics Department, University of Illinois:  Pines, David, and Ulam Scholar. Understanding High Temperature Superconductivity: Progress and Prospects. Center for Nonlinear Studies at Los Alamost National Laboratory and Physics Department, University of Illinois:  Superconductivity for Electric Systems. U.S. Department of Energy:  Superconductivity for Electric Systems. U.S. Department of Energy:  Vidali, Gianfranco. Superconductivity: The Next Revolution? Cambridge: Cambridge University Press, 1993.