AFM correlation and the pairing mechanism in the iron pnictides and the (overdoped) cuprates Fa Wang...
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Transcript of AFM correlation and the pairing mechanism in the iron pnictides and the (overdoped) cuprates Fa Wang...
AFM correlation and the pairing mechanism in the iron pnictides and the (overdoped) cuprates
Fa Wang (Berkeley)Hui Zhai (Berkeley)Ying Ran (Berkeley)A. Vishwanath (Berkeley)
Collaborators
Fa Wang et al, PRL 102, 047005 (2009) Fa Wang, Hui Zhai & DHL, EPL 85, 37005 (2009)Hui Zhai, Fa Wang & DHL, Phy. Rev. B (in press)
Fa Wang Hui Zhai
• Heavy fermion compounds, e.g., CeCoIn5, CeRhIn5, YbPd2Sn, CePd2Si2, CeIn3
Mathur et al, Nature, 394, 39 (‘98)
Systems with superconductivity near antiferromagnetic order
• Organic Compounds, e.g., -(BETS)2FeBr4, -(BEDT-TTF)2Cu[N(CN)2]Br
BEDNORZ, MULLER, Z. PHYSIK B-COND MAT 64 189 (86). M.K. WU et al PHYS. REV. LETT. 58 908 (87).
The Question
Does the AFM correlation have anything to do with the pairing mechanism in these materials?
Let’s focus on the iron pnictides and the cuprates.
Method: Functional Renormalization Group (FRG)
There is a lack of an ideal `ab initio' method for (strongly) correlated systems.
• FRG: Unbiased, applicable to infinite system, but lacks a small parameter (such as the in 4-) to justify it rigorously.
• Exact diagonalization, Quantum Monte-Carlo,DMFT, Mean-field, Variational method, LDA, each has its own limitation.
Results for the (overdoped) Cuprates
Approach from the overdoped side
k1 k3
k2 k4
Pairing mechanism
Dual scattering processes !
A
B
AFM driven correlations
Note that SDW correlation grow over a very wide energy scale. It is not due to nesting.
FRG results for the iron pnictides
Recent FRG resultsC. Platt, C. Honerkamp, W. Hanke, arXiv: 0903.1963
FeAs trilayer
k1 k3
k2 k4
k1+k2=k3+k4
2 x 106 scattering vortices have to be re-evalueated at each step of RG
• Order parameter has opposite sign on electron and hole FS.• The gap function has large variations.• Large variation of the order parameter around some FS.
I. I. Mazin, et al. PRL 101, 057003 (2008) (LDA)K. Kuroki et al PRL 101, 087004 (2008). (LDA)Z.J. Yao et al, New J. Phys. 11, 025009 (2009) (FLEX)K. Seo et al, PRL 101, 206404 (2008). (Exchange model)
Gap variation
• The degree of gap anisotropy depends on microscopic parameters.• It originates from the orbital dependence of pairing.• It should be considered when fitting NMR and heat transport measurements.
Subleading pairing channels
SDW and orbital current order
Two types of Pomeranchuk instability
•This is a band version of “orbital ordering”. •Expect this type of distortion to couple strongly with AFM.• Give rise to Lattice distortion.• Brings in magnetic anisotropy in the AFM ordered state.
Pairing Mechanism
Dual scattering processes !
A
B
AFM driven correlations
SC
AFM
Current order
PI
AF correlation grow over a very wide energy range hence it is notdue to nesting. However whether the AFM will be surpassed by SC does depend on how well the FS are nested.
Gap function
Pnictide Ladder RG results
Conclusion
Thank You !