Types of Superconductors| Types of Superconductors |
In General
* Type I: The ones in which
λ < ξ; They have positive wall energy and
are not so useful, they can't be used for magnets.
* Type II: The ones in
which λ > ξ; They have negative wall
energy, maximize surface and create vortices, quantized in units of
φB = hc/2e; This
type includes all high-Tc superconductors.
* BCS vs unconventional (non-BCS):
In conventional (BCS) superconductors the pairing interaction arises from
lattice distortions, in other superconductors the mechanism is different;
For example, there is evidence that ferromagnetic fluctuations provide the
pairing force in UCoGe.
* Examples: The heavy fermion
compound UPt3; UCoGe, an exotic type in
which ferromagnetism and superconductivity seem to happily coexist.
@ Various materials:
news pw(02)jan;
Canfield & Bud'ko SA(05)apr [MgB2];
Michelle Phy(08)
[iron pnictides and other iron compounds];
Day PT(09)aug [iron-based];
Donnelly PT(09)oct [He, Tisza's contributions];
Julian Phy(02)feb [UCoGe];
Dave et al PRL(13)
+ news(13)mar [cuprates, current and Luttinger's theorem];
Song et al PRL(16)
+ Phy(16) [two distinct mechanisms in FeSe];
news Phys(20)feb [twisted bilayer graphene].
@ Unconventional: Scalapino RMP(12) [arguments for pairing mediated by spin fluctuations].
@ Other special types:
Arutyunov et al PRP(08) [1D systems].
High-Temperature Superconductivity
> s.a. Insulators.
* History: 1986, Discovery and
almost immediate hopes for room-temperature superconductors; 2004, 2016, Still not
completely understood and no Tcs near
room temperature; Theorists suspect that metallic hydrogen might be superconducting
at room temperature; 2019, Simulations with lattices ultracold atoms playing the role
of electrons with tunable parameters may provide clues.
* Properties: Usually very
anisotropic (the energy gap is direction-dependent).
* Mechanism: 2004, It is widely
believed that the classic BCS theory cannot explain it; Cooper pairs are involved but
it is not clear what holds them together; There are claims that interactions between
phonons and electrons or magnetic resonances are relevant, but recent experiments seem
to rule those explanations out; 2008, Electron-phonon interactions can only account for
a fraction of the behaviour; 2017, Cuprates (Tc
= 134 K) have vortex states, so they may be conventional superconductors after all.
* Examples: The most common one by far is YBCO
(YBa2Cu3O7).
@ Books, reviews: Ginzburg SPU(91) [rev];
Cyrot & Pavuna 92;
Holton et al AS(96)jul [discovery];
Nowotny & Felt 02 [r PT(98)mar];
Kresin & Wolf RMP(09) [electron-lattice interaction];
Zaanen a1012-ch [history];
Lederer a2007 [history, on scientific errors].
@ News: Maddox Nat(90)apr;
Hamilton Sci(90)oct
[Tc = 125 K];
news pw(06)aug [evidence for role of phonons];
news pw(06)sep [decline in number of publications];
news pn(07)jul [and Mott insulator properties];
news PT(08)jan [use on the power grid];
news pw(08)apr [not explained by phonons];
Norman video Phy(10) [layered iron arsenides];
Bovensiepen Phy(10)aug [relaxation of excited electrons and phonons];
news pw(10)aug [role of fractals];
news mt(11)apr
[role of next-nearset neighbor interactions in superconductivity in iron-based compounds];
news caltech(11)dec [proposed explanation];
Dal Conte et al sci(12)mar
+ news PhysOrg(12)mar [fine-grained data on electron relaxation its effects on the superconductor];
news at(12)jun [quantum fluctuations rather than changes in temperature or pressure may be a key];
news ls(13)aug [unexpected magnetic excitations];
news pw(15)aug [hydrogen sulfide becomes superconducting at a record 203 K
(–70 °C), when under a pressure of 1.5 million bar];
Song & Xue Phy(17) [re cuprates];
Somayazulu et al PRL(19)
+ news sn(18)sep [high-pressure lanthanum-hydrogen compounds, 260 K];
news Phy(19) [simulation using a lattice of ultracold atoms];
news Phy(19)aug,
sn(19)aug [proposed, above room T, superhigh p];
news sn(20)apr [pair-density wave seen in cuprate];
news sn(20)oct [squeezed C, H and S at very high pressures, 15°C].
@ Theory: Davydov PRP(90);
Kulic PRP(00);
Lanzara et al Nat(01)aug [phonon-electron];
Herbut PRL(05)cm/04 [effective theory];
Alexandrov PS(11) [developments in the bipolaron theory];
Sachdev PRX(15) [entropy, and Bekenstein-Hawking entropy];
> s.a. physical theories [scientific pluralism].
In Particle Physics and Field Theory
> s.a. cosmic strings [superconducting]; QCD [vacuum].
* Color superconductivity: A property of the
ground state of QCD at high densities and low temperatures, believed to involve Cooper pairs of quarks.
@ Color superconductivity: Shovkovy FP(04) [lectures];
Alford et al RMP(08)-a0709 [in dense quark matter];
Anglani et al RMP(14) [and astrophysics].
@ Holographic superconductors: Horowitz LNP(11)-a1002 [introduction];
Brito et al PLB(14)-a1211 [domain-wall description of superconductivity];
Musso a1401-ln [intro].
main page
– abbreviations
– journals – comments
– other sites – acknowledgements
send feedback and suggestions to bombelli at olemiss.edu – modified 15 oct 2020