1. ‘Tc’ ~ 70 K: Fe-Based SC 200 Tc (K) 100 1970 1980 1990 2000 2010 year
1UC FeSe on STO
100
~ 70 K
55 K
SmFeAsO
2012
LaFeAsO
2008
LaFePO
2006
1970
1980
1990
2000
2010
year

2. FeSe Monolayer on a SrTiO3 Substrate
Tc = 65±5 K (100 K ?) Se Fe Se
SrTiO3
I. Mazin, Nature Mater. 14, 755 (2015).
Review
Dung-Hai Lee, Chin. Phys. B 24, (2015).

3. FeSe Monolayer on a SrTiO3 SubstrateTc
S. He, Q-K. Xue, X.J. Zhou et al., Nature Mater. 12, 605 (2013).

4. FeSe Monolayer on a SrTiO3 SubstrateTc
Tc = 108 K ??
Science Bulletin 60 (14), (2015)
S. He, Q-K. Xue, X.J. Zhou et al., Nature Mater. 12, 605 (2013).
Z. Zhang, D.-L. Feng, Yayu Wang et al., arXiv:
J.F. Ge, Q.K. Xue et al., Nature Mater. 14, 285 (2015).

5. Z. Zhang, K.A. Moler, D.L. Feng, Yayu Wang, arXiv: 1507.00129;
Onset of Meissner effect in FeSe monolayer on Nb doped SrTiO3 substrate
Z. Zhang, K.A. Moler, D.L. Feng, Yayu Wang, arXiv: ;
Science Bulletin 60 (14), 1301 (2015)

6. Low-energy mSR: Depth profile

7. Thickness dependence of Tc for FeSe films on STO80 60
Tc (K) 40
electron doping
applying pressure
Y. Mizuguchi et al., Appl. Phys. Lett. 93, (2008).
Medvedev et al., Nature Materials 8, 630 (2009).
Margadonna et al., Phys. Rev. B 80, (2009). 20
1UC
2UC
3UC
4UC
50UC
∞UC
FeSe Thickness

8. Pressure dependence of Tc for bulk FeSe
J.P. Sun, T. Shibauchi et al., arXiv: ; Nat. Commun. 7, (2016)

9. Thickness dependence of Tc for FeSe films on STO80 60
Tc (K) 40
electron doping
applying pressure
Y. Mizuguchi et al., Appl. Phys. Lett. 93, (2008).
Medvedev et al., Nature Materials 8, 630 (2009).
Margadonna et al., Phys. Rev. B 80, (2009). 20
1UC
2UC
3UC
4UC
50UC
∞UC
FeSe Thickness

10. Thickness dependence of Tc for FeSe films on STO80
C. Tang, Q.-K. Xue et al., arXiv: ; Phys. Rev. B92, (R) (2015). 60
Y. Miyata, T. Takahashi et al., Nature Mater. 14, 775 (2015).
Tc (K)
C.H.P. Wen, D.-L. Feng et al., arXiv: ; Nat. Commun. 7, 40
J. Shiogai et al., Nature Phys. 12, 42 (2016). 20
1UC
2UC
3UC
4UC
50UC
∞UC
FeSe Thickness

11. SC of 2UC-FeSe (double-layer) on STO
C. Tang, Q.-K. Xue et al., arXiv: ; Phys. Rev. B92, (R) (2015).

12. Electron Doping into FeSe Films on STO
K deposition
Electric field
SrTiO3 MgO
Y. Miyata et al., Nature Mater. 14, 775 (2015).
J. Shiogai et al., Nature Phys. 12, 42 (2016).

13. Electron Doping into FeSe Films on STO
K deposition
Electric field
Y. Miyata et al., Nature Mater. 14, 775 (2015).
J. Shiogai et al., Nature Phys. 12, 42 (2016).

14. Electron Doping into FeSe Films on STO
K deposition
C.-L. Song, Q.-K. Xue et al., arXiv: ; Phys. Rev. Lett. 116, (2016).
Y. Miyata et al., Nature Mater. 14, 775 (2015).

15. Electron Doping into FeSe Films on STO
I. Mazin, Nature Mater. 14, 755 (2015).

16. FeSe Monolayer on SrTiO3: Interface Effect (1)
Tc = 65±5 K Se Fe
Interface effects :
Electron transfer (doping) from O vacancies in the STO surface layer (?)
Doping/transfer is only to the bottom FeSe layer – Open question (?) Se
SrTiO3 Se O O
Dung-Hai Lee,Chin. Phys. B 24, (2015). Ti Ov
Review O

17. Interface Atomic Structure: 1UC-FeSe on STO
F. Li, Q.-K. Xue et al., arXiv: (State Key Labo. of Low-Dimensional Quantum Physics, State Key Labo. of New Ceramics and Fine Processing, Tsinghua Univ.) Se O O Ti O OV Ti O O Sr
TiO2-x

18. FeSe Monolayer on SrTiO3: Charge Transfer (?)
Hao Ding, Q-K. Xue et al., arXiv: ; Phys. Rev. Lett. 117, (2016).
J. Shiogai et al., Nature Phys. 12, 42 (2016).

19. Enhanced Tc in Monolayer FeSe on STO80
C. Tang, Q.-K. Xue et al., arXiv: ; Phys. Rev. B92, (R) (2015). 60
Y. Miyata, T. Takahashi et al., Nature Mater. 14, 775 (2015).
Tc (K)
C.H.P. Wen, D.-L. Feng et al., arXiv: ; Nat. Commun. 7, 40
J. Shiogai et al., Nature Phys. 12, 42 (2016). 20
1UC
2UC
3UC
4UC
50UC
∞UC
FeSe Thickness

20. FeSe Monolayer on a SrTiO3 Substrate
Tc = 65±5 K Se Fe
Interface effects :
Electron transfer (doping) from O vacancies in STO (?)
An additional pairing channel from a coupling with the bond-stretching O vibrations (W0 ~ 100 meV) in SrTiO3. Se
SrTiO3 Se O O
Dung-Hai Lee,Chin. Phys. B 24, (2015). Ti OV
Review O

21. FeSe on STO: Interface Effect (2)
Dung-Hai Lee,　Chin. Phys. B 24, (2015).

22. Proposed 1UC FeSe-TiO Complex
Dung-Hai Lee,Chin. Phys. B 24, (2015).

23. Enhanced Tc in Monolayer FeSe on STO80
Tc = 60 K-class SC cannot be achieved by bulk and thicker films of FeSe. 60
Tc (K) 40 20
1UC
2UC
3UC
4UC
50UC
∞UC
FeSe Thickness

24. Summary of Tc and Gap in Bulk, Doped, and Monolayer FeSe
S.N. Rebec, Z.-X.. Shen et al., arXiv:

25. Interface Atomic Structure: 1UC-FeSe on STO
F. Li, Q.-K. Xue et al., arXiv:
aFeSe = 3.86 Å　 (3.76 Å)
hSe = 1.31±0.01 Å (1.45 Å )
dSe-Ti = 3.58 Å
hSeopt = 1.38 Å
a = 111.4°±0.9° (103.6°)
a opt = 109.5°
bulk FeSe

26. FeSe Monolayer on a SrTiO3 (110) Substrate

27. Small Electron Fermi Surface Pockets in FeSe
L.P. Gor’kov, arXiv: ; Phys. Rev. B 93, (2016)..
B. Rosenstein et al., arXiv:
● Validity of Migdal theorem
- low EF
The Fermi energy is small; EF ~ ħW0
EF ~ 60 meV
ħW0 ~ meV EF
m* = m / [1 + m ln (EF/ħW0)]

28. s-Wave SC Gap in Monolayer FeSe on STO
Q. Fan, D.-L. Feng et al., Nature Phys. 11, 946 (2015).

29. Exfoliated Monolayer Materials
Anomalous charge transport

30. Exfoliated Monolayer Materials
“Magnetic graphene”
MPS3 (M: 3d-TM, Mn, Fe, Co, Ni)
J.-G. Park (IBS-CCES, Seoul)
Anomalous charge transport
Bulk single crystal
P.A. Joy & S. Vasudevan, PRB 46, 5425 (1992).

31. Families of Iron-Based SuperconductorsSr O V As Fe
FeSe
Sr4V2O6Fe2As2
LaFeAsO
BaFe2As2
LiFeAs
Tcmax = 55 K
Tcmax = 39 K
Tcmax = 22 K
Tcmax = 8 K
Tcmax = 38 K

32. Families of Iron-Based SuperconductorsSr O V As Fe
FeSe
Sr4V2O6Fe2As2
BaFe2As2
LaFeAsO
LiFeAs
KxFe2-ySe2
Ca4(Mg, Ti)3Fe2As2O8-y
(Ca, La)Fe2As2
Tcmax = 55 K
Tcmax = 39 K
Tcmax = 22 K
Tcmax = 8 K
Tcmax = 38 K
Tcmax = 55 K
Tcmax = K
Tcmax = K
Tcmax = 47 K
Already optimized !?

33. Why is Fe-As(Se) unique ? Tc vs Bond Angle
1UC FeSe
FeSe

34. Tc vs Pn/Ch Height
1UC FeSe
Y. Takano (NIMS)