Future of Superconductivity Paul M. Grant Science Fellow EPRI pgrant@epri.com

1911 A Big Surprise! Thus the mercury at 4.2 K has entered a new state, which, owing to its particular electrical properties, can be called the state of superconductivity H. Kamerlingh-Onnes (1911)

Magnetic Susceptibility -1/4  T H off H on -1/4   T H on H on Expected (Lenz’ Law) Weird ! (Meissner Effect)

“Cooper’s Problem”  = N(EF) V0

“Cooper Pairs” California Style

BCS Origin of   = N(EF) V0 -/a /a -/2a /2a quasi-momentum (k) Energy EF 4 N(EF) = 1/(dE(k)/dk) = 1/[2 {1-(EF/2)2}1/2] E(k) = 2 cos(ka) N(EF) ~ -1 ~ [ AUB d ]-1  = N(EF) V0 V0 ~ A(UB) d

Strong Coupling (1) McMillan/Eliashberg Equation: “Coulomb Repulsion:” “Dimensionless electron-phonon Coupling Term:”

Strong Coupling (2) “Tunnel Spectral Term” e-p matrix element deformation potential matrix element

TC vs Year | 1911 2001 1930 1950 1970 1993 1988 1987 1986 20 K 140 K 40 K 60 K 80 K 100 K 120 K Absolute Zero Helium Boils Hydrogen Nitrogen Methane Hg La-214 Y-123 Bi-2223 Tl-2223 Hg-1223 Nb Compounds MgB2 p-C60

Theory Situation “Gap” line “Triple Point” No complete quantitative theory exists (i.e., “computable”) “Simple” superconductors can be dealt with by M-E quasi-quantitatively TC for hex-Si was predicted MgB2, C60, (SN)x can be “explained” 15 years after their discovery, there is still no accepted microscopic theory for layered copper oxide perovskites “We may never know exactly what interactions play out at the triple point.” Bob Laughlin

Type II Superconductivity  = / > 1/2 Irreversibility Line Meissner Mixed Normal HC2 HC1 Magnetic Field TC Temperature -M H 1/4p

Abrikosov Vortex Lattice H Dipole Force FP = FP(0) [1-(T/TC)]n J FLorentz Type II Superconductor in the Mixed State

Vortex Matter “The Party’s Over” Thermally activated Tinkham, PRL 61, 1658 (1988) Static Phase Diagram Temperature Magnetic Field Dynamic Phase Diagram TC HC2 HC1 FLorentz Elastic Flow Plastic Flow Liquid Flow Normal Liquid Glass Solid Bose Glass Polymer Glass Melting Line Meissner State SC Fluctuation Regime R/Rn = {I0[A(1-t)3/2/2B]}-2 T = T/TC Thermally activated flux flow possible Showstopper for “real high” TC

ac Losses H M

Superconductivity Yesterday Magnetic Resonance Imaging Philips Tevatron Fermi National Laboratory

Important Numbers in Superconductivity Transition Temperature, TC Way below 300 K Critical Current Density, JC 10-2 - 106 A/cm2 Critical Magnetic Field, HC 10-4 - 10 T London Penetration Depth,  10 - >1000 Å Pippard Coherence Length,  10 - >1000 Å Mean Free Path, l 150 – 5000 Å G-L Parameter,  = / 0.01 - 100 NB! All these numbers depend on each other. E.g., HC ~ TC ~ 1/

Metrics of Superconductors Operating Temperature (~ 2/3 TC) Irreversibility Field (~ 70% HC2) Operating Current (~ 80% JC) Wire/Cable Weight Cryogenic Load (cooling watts/plug watts) Cost ($/kAm)

Power Application Specs Figure taken from: T, H, Jc requirements roughly reflect those of current DOE Superconductivity Partnership Initiative Projects T(K) = 25 - 40 25 - 77 H(T) = 1 - 4 0.5 - 2 Jc(A/cm2) = 154,000 – 192,000 7,000 – 231,000 R. D. Blaugher, NREL

Power Device Req’mts T (K) H (T) Jc (A/cm2) Motors/ Generators 30 4 100,000 Transformers 2 80,000 Current Limiters Cables 77 0.5 70,000 Specifications roughly reflect requirements of present DOE Superconductivity Partnership Initiative projects. See www.eren.doe.gov/superconductivity.

Merit Factor for Superconducting Wire: Wire Cost Issues Merit Factor for Superconducting Wire: C/P = $/kAmp × meters Wire C/P Cost Driver NbTi (4.2 K, 2 T) 0.90 Materials (Nb) Nb3Sn (4.2 K, 10 T) 10 Bi-2223 (25 K, 1 T) 20 Materials (Ag) Y-123 (25 K, 1 T) 4 Capital Plant Above data drawn from the following paper presented at the 1998 Applied Superconductivity Conference held in Palm Desert, CA. C/P adjusted from projected $50/kAm for Bi-2223 and $10/kAm for Y-123 wire at 77 K, self field, as their commercial goals to 25 K, 1 T.

Superconductivity Today Frisbie Substation, Detroit, 2001

Gen I has Problems… Silver is one… JC Paths @ 12 K > 3.6105 A/cm2 > 2.6105 A/cm2 > 1.6105 A/cm2 = 0 A/cm2

HTS Tape Gen II: It’s Coming! “1-2-3 is Better” Y Ba CuO Pyramids Chains Planes YBa2Cu3O7-y TC = 93 K JC > 106 A/cm2 JC > 105 A/cm2 (1 T)

Coated Conductors Generation II Wire Biaxially Oriented Y-123 Out of Japan, LANL, ORNL DOE/Industry Alliance to Commercialize

Frisbie Cable

Men at Work

Men at Work, II

Men at Work, III

Pull Visualization

Finding New Superconductors “Advances in superconductivity begin with the empirical search for new materials.” Bednorz and Mueller, Z. Phys., Sept., 1986 “No new superconductor was ever found using theory.” Berndt Matthias “If you run across a strange metal, new or old, it’s a good idea to cool it down…you might get a surprise. P. M. Grant

Nature, 1 March 2001 How was it ever missed!

Maybe It Wasn’t ! ? 39 32

Cost Issues: MgB2 Alfa Aesar Assumptions/Givens: JC = 100,000 A/cm2 IC = 2000 A/wire (Area = 2 mm2) Non-Materials C/P = 0.11 $/kA•m (NbTi) Alfa Aesar MgB2 Price Quote (10 kg) 750 $/kg (0.75 $/gm) MgB2 Wire C/P 2.03 $/kA•m @ 25 K, 1 T The following calculation assumes an eventual non-materials basic manufacturing cost (BMC) similar (in this case equal) to that of present commercially available NbTi wire. 10 kg batch quote from Alfa Aesar on 8 March 2001.

The Nuclear/Hydrogen/Superconductivity It’s 2015 A World at Peace Global Climate at Risk Continuing Industrialization Reaches All Corners of the Planet The Nuclear/Hydrogen/Superconductivity Economy at last!

Climate Friendly Energy National Climate Change Technology Initiative (NCCTI – “Necktie”) “Absolutely Zero GHG Emissions by 2050” George W. Bush MgB2 1/5/01 40 K Cheap Fall Issue, The Industrial Physicist Tunnels Fermilab 2 m Dia. 150 m Deep Cheap

“The 60-fold Way”

“Little” Model TC ~ 400 K !!! = “hole-exciton” coupling W. A. Little, Sci. Am. 212, 21 (1965) “Conducting Polyene Spine” “Paired Holes” = “hole-exciton” coupling (“weak,” ~ 0.25) “Polarizable Side Groups” ”E” = “exciton energy” (~ 2 eV, ~ 23,000 K) TC ~ 400 K !!!

“The 60-fold Way” The separation between the electronic states and vibrational modes of C60 exploited by Schön et al. is just the sort of thing Little had in mind in the 1960s when he proposed his ‘excitonic’ model of superconductivity.

The Future 2028 Is “Room Temperature” Superconductivity Possible? Why Not? 2028

Defense Drivers for Superconductivity Many “weapons” need power…lots of it Ships, planes, tanks, KE devices, … Launch technologies SC cables, generators, motors, storage… Hardened Infrastructure Everything underground Power (electrical/chemical) superhighway Maglev

R&D Road to 2020 Old materials (survey) New materials (empirical, exotic) Combinatorial chemistry (???) Computational Chemistry & Physics “Configuration Interaction” Role of “dimensionality” Luck !

“You can’t always get what you want…”

“…you get what you need!”

“Gap” line