Superconductivity: there’s plenty of cream at the bottom P.J. Hirschfeld, U. Florida
SESAPS, 6 November 2020 Superconductivity B Shivaram U Chatterjee
S Johnston T Maier E Dagotto A Moreo N Manella L Kemper D Kumah C DeMelo, HB Schuettler, M Geller T. C l ay I Vekhter S Sarker P Adams
G Boebinger, D Larbalestier, K Yang, G Stewart, J Hamlin, O Vafek, Y Wang, D. Maslov, L Greene, L. Steinke, D. Laroche, D Popovic, A. Biswas, HP Cheng, PJH L Balicas Collaborators SC theory
from rest of world:
from U. Florida Dept. of Physics: Roser Valenti Brian Andersen (Frankfurt) (Niels Bohr)
Doug Scalapino Thomas Maier UCSB ORNL
Vivek Mishra Maxim Korshunov Lex Kemper Hai-Ping Tom Berlijn (ORNL) (Krasnoyarsk) (NC State) Cheng (ORNL) Andrey Chubukov Igor Mazin, GMU U. Minn.
Saurabh Maiti Peayush Shinibali Andreas Kreisel YanWang (Concordia U.) Choubey Bhattacharyya Indranil Paul, Ilya Eremin, (Leipzig) (ORNL) (Bochum) Paris-VII Bochum Discovery of superconductivity
Heike Kammerling Onnes (1911) Conventional superconductors
•During 46 years, from 1911 to 1957, superconductivity is recognized as one of the most important problems in theoretical physics - Search for a theory of superconductivity: series of failures (see J. Schmalian in 50 Years of BCS)
Richard Feynman: “No one is brilliant enough to figure it out”
Fail: F Fail: F Fail: F Fail: F Fail: F
Heisenberg Bohr Landau Feynman Einstein Conventional superconductors
BCS theory (1957)
Quantum mechanical behavior at the macroscopic scale
Leon Cooper Nobel prize : 1972
John Bardeen Robert Schrieffer
Macro. Quantum State uvcc |0 BCS k k kk k i s-wave symmetry Vc-k ck ~ e SC Ground State
Superconducting Normal State (Metal) Low Temp. Ground State Cooper Pairing KY KY KY L=0 S=0
K K KX X |k> |-k> K X K KF F F
Degenerate ~free electron gas ~ Gas of Cooper Pairs Superconductivity: why is pairing good?
Naive answer: once we have an attraction, we get pairs. Pairs of fermions are bosons, so they can Bose condense pair superfluid
S=0
Q: is this the right picture of a BCS superconductor? A: No! Superconductivity: Ground state
In reality, Remember that all pairs -1/3 are phase coherent! vF>> n
Simple metal: ~ 103 A n-1/3 ~ 1A
St. Matthew’s Passion Oxford, UK How Cooper pairs form in conventional superconductors: the “glue”: electron-phonon interaction
+ + + + + + + + + + + + + + + + + + + + + + + + + + ------+ + + + + + + + + + + + + + + + + + + + + + + + + + + +
Effective “residual” ab For realistic system, e-e interaction ab! Depends on including Coulomb details (“Jellium model”) Screened Coulomb Electron-phonon attraction
Note: electrons avoid Coulomb repulsion in time (interaction is retarded) Why do some elements superconduct, others not?
a,b depend on a b details! Is that all there is? Brian Pippard and “The Cat and the Cream” speech IBM 1961 Is that all there is? Brian Pippard and “The Cat and the Cream” speech IBM 1961
“I think I might remark that in low- temperature physics the disappearance of liquid helium, superconductivity, and magneto- resistance from the list of major unsolved problems has left this branch of research looking pretty sick from the point of view of any young innocent who thinks he's going to break new ground.” 1979: superconductivity in “heavy electron“ systems
“effective masses” of electrons ~ 100- 1000 times larger than bare electron mass!
Pairing by electronic rather than ionic excitations? 1986: High temperature superconductivity in cuprates
Z. Physik, June 1986
Alex Müller and Georg Bednorz Great expectations 1987 Power Efficiency/Capacity/Stability Power Density Renewable Power
Efficient Power Generation Quantum Technology Next Generation HEP
HE Accelerators Science / Medicine
Future Particle Accelerators Medical Technology Fusion Tokomak kk cos cos -wave SC: d 0 2 kxy -wave d Cuprates are are Cuprates What holds pairs together? is too high for electron-phonon “glue” to work! c T 2 paradigms for superconductivity according to how pairs choose to avoid Coulomb interaction
“conventional” : isotropic s-wave pair
wave fctn, interaction retarded in time
Overall effective interaction attractive
“unconventional”: anisotropic or sign-changing pair wave fctn,
Overall effective interaction repulsive 2008: discovery of LaO1−xFxFeAs
Kamihara et al JACS 2008 Tc=26 K
H. Hosono
Monolayer FeSe 2014:
Group of M. Eremets (Mainz) 2018: Tc=250-260K in LaH10 R. Hemley (Carnegie), M. Eremets (Mainz)
“Clathrate”-type structure Room temperature superconductivity?
H3S under 2 Mbar pressure: Tc=210K = -63C = Lowest recorded temperature in Yakutsk
LaH10 under 1.5 Mbar pressure: Tc=250K = -23C = average low temperature in Yakutsk in November
Challenge: duplicate physics of hydrides & related high-pressure SC at ambient pressure Room temperature superconductivity?
H2S+CH4+H2 mixture under 2.6 Mbar pressure: Tc=288K = 15C = 59F = average temperature in Yakutsk in June!
Snider et al, Nature October 14 2020 ~1.1o
Moire’ pattern Is magic angle graphene analogous to cuprates???
MATPG Cuprates
Mott metal Conclusions/questions
• Two paradigms for superconductivity: “conventional” (el- ph, retarded in time, “unconventional” (electronic excitations, higher angular momentum pairs).
• Are there several families of SC linkedThank by you! common pairing mechanism—”common thread”?
• Superconductivity in twisted bilayer graphene (Herrera, 2018)
• Superconductivity at 200K in H3S under pressure (Drozdov et al 2015…Snider et al 2020). No limit on e-ph Tc!
• Superconductivity: a field that constantly renews itself!