1. ARPES studies of unconventional
superconductors
Hong Ding
Institute of Physics, Chinese Academy of Sciences
Swiss architecture firm Herzog & de Meuron
Heavy Fermion Physics Workshop, January 9, 2012

2. Phase diagrams
pnictide SC
heavy fermion SC
organic SC
cuprate SC

3. Fermi surface mapping of cuprates
Bi2Sr2CaCu2O8
Tight binding fitting
Large FS, area = 1-x: Luttinger’s theorem

4. d-wave superconducting gap in cuprates
Half-Integer Flux Quantum Effect

5. Pseudogap in underdoped cuprates

6. Phase diagram of Ba122 system
Electron doping
Hole doping
Electron-hole asymmetry?
M. Neupane et al., PRB 83, (2011)

7. ARPES observation of five bands and five FSs

8. Fermi surface evolution in “122”
Heavily OD
Slightly OD
OPT UD
QAF
Tc = 3 K
Tc = 22 K
Tc = 37 K
Tc = 26 K
Hole doping
Parent UD
OPT
Heavily OD
QAF
TN = 135 K
Tc = 0 K
Tc = 11 K
Tc = 25 K
Tc = 0 K
Electron doping

9. ARPES observation of superconducting gap
2/Tc ~ 7
H. Ding et al., EPL 83, (2008)

10. Nodeless SC gap in Ba0.6K0.4Fe2As2 (Tc = 37K)
H. Ding et al., EPL 83, (2008)
K. Nakayama et al., EPL 85, (2009)

11. - + J1 – J2 model predicts almost isotropic s± gap +
Order parameters in
momentum Space
Real space configuration
of pairing symmetry
local interactions
J1- J2 - + +
pnictides: large J2 and FS topology favor
D = D0 coskxcosky, s±-wave
cuprates: large J1 and FS topology favor
D = D0 (coskx–cosky)/2, d-wave
K. Seo, A. B. Bernevig, J. Hu PRL 101, (2008)

12. Most weak-coupling theories predict anisotropic s± gap
D.H. Lee
EPL 85, (2009)
I. Mazin
PRB 79, (2009)
S. Graser
NJP 11, (2009)
when

13. overdoped Ba0.3K0.7Fe2As2 (Tc ~ 20K)
K. Nakayama et al., PRB 83, (R) (2011)

14. underdoped Ba0.75K0.25Fe2As2 (Tc = 26K)
Y.-M. Xu et al.,
Nature Communications
2, 392 (2011)

15. Doping dependence of the SC gaps in Ba1-xKxFe2As2
K. Nakayama et al., PRB 83, (R) (2011)

16. Electron doped BaFe1.85Co0.15As2 (Tc = 25.5K)
K. Terashima et al, PNAS 106, 7330 (2009)

17. kz dependence of SC gaps
single gap function
Jab = 30
Jc = 5
D2/D1
≈ Jc/Jab
≈ 0.17
Y.-M. Xu et al., Nature Physics 7, 198 (2011)

18. “111” - NaFe0.95Co0.05As (Tc = 18K)
Z.-H. Liu et al., arXiv: , PRB

19. “11” - FeTe0.55Se0.45 (Tc = 13K)

20. J1 = -34
J2 = 22
J3 = 6.8
D2/D3
≈ J2/J3
≈ 0.3
H. Miao et al., arXiv:

21. (Tl,K)Fe2-xSe2 (Tc ~ 30K)
T. Qian et al., PRL (2011)

22. Isotropic SC gap on electron FS
J1 < 0, FM, d-wave is not favored
X.-P. Wang et al., EPL 93, (2011)

23. Selection Rules of Pairing Symmetry
Self-consistent meanfield equation for t-J model
Overlap strength between pairing form factor and Fermi surface
OS =

24. Three classes of high-Tc superconductorsJ1 J2
J2+J3

25. Three classes of high-Tc superconductorsJ1 J2
J2+J3

26. Summary
The SC gap of all iron-based superconductors measured by ARPES can by described approximately by J1-J2-J3 model
A possible unified paradigm of high-Tc superconductivity:
local AFM magnetic exchange
+ collaborative FS topology
J.-P. Hu and H. Ding, arXiv: