Superconductivity. Allen M. Goldman. School of Physics and Astronomy University of Minnesota

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1 Superconductivity Allen M. Goldman School of Physics and Astronomy University of Minnesota October 26, 2007

2 OUTLINE Introduction What is superconductivity? Phenomena Mechanism Superconducting Materials Impacts of HTS and LTS Challenges

3 Superconductivity is: Scientifically Challenging - offers new paradigms for our understanding of solids & physics Technologically Promising - may hold the key to the sustainable development of the world

4 Traditional Path for Industrialization (sustainable development is needed and HTS technology could play a key role) China? (Xu K. D., President, CAE) GDP Per Capita

What is Superconductivity? Zero Resistance Absolute Temperature Scale 0 Kelvin is -273 0 C Resistance goes to zero at a characteristic temperature.

5 What is Superconductivity? Zero Resistance Absolute Temperature Scale 0 Kelvin is C Resistance goes to zero at a characteristic temperature. This data is from Kammerlingh-Onnes in 1911, and shows the onset of superconductivity in the element mercury. Data actually taken by Hulst. Applications: Power lines, magnets, motors, generators

6 Flux Exclusion Perfect conductor Superconductor Superconductors exhibit nearly perfect diamagnetism below some characteristic field: Meissner-Ochsenfeld Effect-Type I Superconductors

7 Levitation Levitation

8 Persistent Currents Superconducting Magnets for MRI, accelerators, crystal growth, etc.

9 Flux Quantization Magnetic Flux = Magnetic Field x Area Flux is quantized in units of hc/2e Planck s constant: h Electron charge: e Velocity of Light: c

11 Vortex Lattice of a Type II Superconductor For Type II superconductors above a certain value of magnetic field, flux enters in the form of a lattice of quantized vortices. Superconductivity can then persist to extraordinarily high magnetic fields.

12 Phase Diagram of a Type II Superconductor

13 Tunneling Tunneling:- electrons transit an insulator that is sufficiently thin. This is an important quantum mechanical effect. For sufficiently thin barriers have the Josephson Effect - the barrier has zero resistance At nonzero voltage, V, the structure radiates: frequency = 2eV/ h Applications: detectors for Astronomy, highperformance computers, magnetometers.

SQUID (Superconducting Quantum Interference Device) Detector of magnetic field that is based on the quantum properties of superconductors Sensitivity:

14 SQUID (Superconducting Quantum Interference Device) Detector of magnetic field that is based on the quantum properties of superconductors Sensitivity: to of the earth s magnetic field. Prospecting for metallic ores Magnetoencephalography Magnetocardiography Low-field MRI Magnetic measurements

15 Mechanism The transition is an example of spontaneous global symmetry breaking. Repulsive interaction of like charges is overcome by over-screening. Electrons pair up--cooper Pairs. Theory: Bardeen, Cooper and Schrieffer (1957) Explains all conventional superconductors and all of the exact properties discussed.

16 The Special Role of the BCS Theory in Science Prediction and discovery of superfluidity in liquid 3 He (Condensed Matter Physics) Pairing in Nuclear Physics, explaining Nuclear Energy Levels (Nuclear Physics) Neutron Stars are Superfluid, Pulsar rate glitches are evidence of vortices (Astronomy) Pairing in Condensed Cold Atoms-Observation of Vortices(Atomic Physics) Color Superconductivity in Compact Stars (Astronomy and Particle Physics) The Higgs Particle (Particle Physics) (spontaneous symmetry breaking, mass) EMERGENT RATHER THAN REDUCTIONIST

17 Examples of Superconductors Nonmagnetic metallic elements Binary and ternary compounds Organic compounds Alkali metal intercalated C 60 Carbon Nanotubes Oxides

18 Historic Evolution of Superconducting Transition Temperatures Superconducting Transition Temperature, T C From Paul Chu (K) Pb Hg Freon LNG Hg-Ba-Ca-Cu-O Tl-Ba-Ca-Cu-O Bi-Sr-Ca-Cu-O Liquid Nitrogen NbN Nb 3 Sn NbC Nb V 3 Si La-Ba-Cu-O # Hg-Ba-Ca-Cu-O # Y-Ba-Cu-O La-Ba-Cu-O # La-Ba-Cu-O Year Nb 3 Ge Nb-Al-Ge Liquid Helium? Ba-Ca-Cu-O # Ba-Ca-Cu-O Mg-B # Under Pressure

19 Structures of High Temperature Superconductors

20 m Generic Crystal Structure EO AO AO EO CuO 2 R CuO 2 charge reservoir block (EO)(AO) (EO) active block (CuO 2 )[(R)(CuO 2 )] n-1 A Bi, Tl, Pb, Cu (AO) E Ca, Sr, Ba R Ca, RE, (REO) e.g. YBa 2 Cu 3 O 7 = CuBa 2 YCu 2 O 7 = Cu1212 R CuO 2 Layered Structure A m E 2 R n-1 Cu n O 2n+m+2 [(EO)(AO) m (EO)] + (CuO 2 )[R(CuO 2 )] n-1 Am(n-1)n 0m(n-1)n

21 Impacts of Superconductivity on S&T Pre-High Temperature Superconductivity (SC) - T c raised (to 23.2 K) - new SC & non-sc compounds discovered. - mystery of SC unraveled (BCS Theory) - viability of SC technology demonstrated [MRI, Accelerators, SQUIDs, possible Quantum Computers and other high performance computers] - new phenomena and physics discovered - understanding non-sc phenomena improved [via interaction with SC] - new material characterization and synthesis tools developed

22 Impacts (cont.) Post-High Temperature Superconductivity (HTS) - T c raised (to 134 K at ambient, 164 K under pressure) - new SC & non-sc compounds discovered - HTS prototypes constructed and demonstrated [cables, FCLs, Transformers, Filters, SQUIDs, MRI sensors] - new phenomena and physics discovered - understanding non-sc phenomena improved [via interaction with SC] - new material characterization and synthesis tools developed also for non- SC

23 Current Status Known HTS - a new paradigm for condensed matter physics More than 150 non-intermetallics with T c > 23 K (Cuprates, Bismuthates, and Fullerites, MgB 2 ) All HTS with T c > 77 K belong to Layered Cuprates HgBa 2 Ca 2 Cu 3 O 8+δ Has the Highest T c = 134 K (at ambient), 164 K (at 30 GPa) H c2 150 T (~ 3x10 6 H earth ) Intriguing generic phase diagram and magnetic phase diagram

24 From Mike Norman

25 More structures - George Crabtree

26 Current Status - Unknown No generally accepted microscopic theory after 20years!

27 HTS Considerations for Science Need intrinsic properties, but the materials are physically intricate, chemically complex and chemically unstable The grand challenge- higher T c -- no new record since 1994!

28 HTS Considerations for Technology Need high performance at low cost and the materials have to be in the proper forms for devices -improved properties via processing & modification -cryogenic efficiency -tedious processing -auxiliary material compatibility -lifetime and reliability

29 A vision for the future!

30 Program at Minnesota Tunneling and Transport in Ordered and Disordered Superconductors - Supported by NSF/DMR (quantum phase transitions) Tunneling and Transport in One-Dimensional Systems -Supported by DOE Basic Energy Sciences (Luttinger Liquid effects, clusters) Interfacial Phenomena in Superconducting Heterostructures -Supported by NSF/DMR and NSF/INT (The doping phase diagram, magnetic/superconducting structures) US-India Collaborative Research -Supported by NSF/INT (penetration depth measurements) University of Minnesota MRSEC-IRGs 2 and 3 Current Group: Sarwa Tan (postdoc), Yu Chen, Xiang Leng, Masaya Nishioka, Alexey Kobrinskii, Yen-Hsiang Lin, Yeon Bae Lee

31 The Superconductor Plague-The Outsiders sold the Puppeteers the location of the Ringworld in 1733 a.d. Searching for a way to expand trade at no risk, the Experimentalists immediately sent robotic probes to determine the feasibility of an expedition.the Puppeteers mistook the City Builders to be the Ringworld's engineers and become suddenly afraid to encounter so powerful a race. The Puppeteers examined the Ringworld's superconductor material and created a technophytic bacterium to seed the Ringworld and destroy the superconductor. The strategy was to follow the probes with trading ships and come to the profitable rescue of the City Builders. However, the Puppeteers quickly realised that the City Builders could not possibly have created the Ringworld, and soon discovered several Pak artifacts. The Puppeteers feared the Pak above nearly all other threats.the Conservatives took control of the government and the Ringworld project was abandoned. The Experimentalists regained power under the threat of Kzinti expansion and decided that a manned expedition to the Ringworld might reveal treasures worth the risk (especially if they could convince others to take the risk for them). When the decision was made, the plague had reduced the Ringworld to barbarism, destroying thousands of years of civilization.

Superconductivity and Superfluidity

Superconductivity and Superfluidity Contemporary physics, Spring 2015 Partially from: Kazimierz Conder Laboratory for Developments and Methods, Paul Scherrer Institute, 5232 Villigen PSI, Switzerland Resistivity