Iron based high temperature superconductors k haule, Rutgers University

Iron based high temperature superconductors

• K Haule, Rutgers University

Technologically relevant

How it all started….

And exploded….

First family of SC

Crystal Structure:Tetragonal I4/mmm

Variety of materials

What is the glue?

Phase diagrams SmFeAsO

Phase diagrams

Common features of the parent compound

Magnetic and structural PT

Fe magnetism ?

Itinerancy & Frustration

Signatures of moments in 1111 compounds

Susceptibility of 122

Nonmagnetic impurities not detrimental to SC

Band structure of LaOFeAs

Importance of Hund’s coupling

ARPES on Ba0.6K0.4Fe2As2

Anisotropy of the gap

Other common possibilities

Conclusions

• Variety of materials with common SDW feature and SC

• 1111: LaOFeAs, CeOFeAs,…SmOFeAs
• 122: BaFe2As2, CaFe2As2
• 111: LiFeAs
• 11: FeSe, FeTe

• Highest Tc~55K achieved in SmFxO1-xFeAs

• Some similarities with cuprates, but also differences (Co doping)

• Correlations weaker than in cuprates (not doped Mott insulators)

• ARPES shows almost uniform gap on FS sheets (s-wave, extended s-wave,….)

• Other probes of gap symmetry are still controversial (1/T1~T3, 1/~exp/powerlaw, Cv~exp/powerlaw)

Optics in LaFeAsO

One more possibility

LaOFeAs under pressure Tc~43K