1. Charge Inhomogeneity and Electronic Phase Separation in Layered Cuprate
F. C. Chou
Center for Condensed Matter Sciences, National Taiwan University
National Synchrotron Radiation Research Center, Taiwan

2. Inhomogeneous Electron Density

3. CDW, Dimerization and Nesting
1d Peierls instability : q = 2kF
CDW => MIT
2d Fermi Surface nesting
Peierls Transition

4. Phase Diagrams
La2CuO4+d
La2-xSrxCuO4

5. Charge Inhomogeneity: Spin and charge stripes
La2-x-yNdySrxCuO4
Holes segregate into AF antiphase domain walls
Tranquada et al, Nature 1995

6. Spin/Charge Stripes and Superconductivity
Yamada et al, PRB 1998

7. 1d domain walls in low x La2-xSrxCuO4
L ~ 1/x
1-TN(x)/TN(0) ~ L-1/n
Finite size effect:
Cho et al, 1993

8. Charge Inhomogeneity: Checkerboard Type
Underdoped Bi2Sr2CaCu2O8+d
Underdoped Ca2-xNaxCuO2Cl2
Hanaguri et al, Nature 2004
Hashimoto et al, PRB 2006

9. Electrochemical oxygen intercalation
La2CuO4+d
Li et al, PRL 1996
La2CuO4
Reference Pt
NaOH/H2O electrolyte V
Grenier et al, Physica C 1991

10. Macroscopic Phase Separation in La2CuO4+d
Electrochemical oxygen intercalation
Undoped AF domain and hope-doped SC domain
La2-xSrxCuO4
Radaelli et al, PRB 1993; Statt et al, PRB 1995

11. Spinodal Decomposition

12. Staging: charge/oxygen segregation
La2CuO4+d
Wells et al, Science 1997

13. Electrochemical oxygen intercalation
La2CuO4+d
La2-xSrxCuO4
La2CuO4
Reference Pt
NaOH/H2O electrolyte V
Grenier et al, Physica C 1991

14. La2-xSrxCuO4+d: hole doping through Srx and Od
Identical SC onset ~40K
SC volume fraction indep. of x or d

15. La2-xSrxCuO4+d: magnetic phase by ZF-mSR
La1.91Sr0.09CuO4+d
Magnetic static ordering onset near ~40K
Magnetic volume fraction independent of x or d

16. Phase Separation?
Co-existing superconducting (SC) and magnetic (ISDW) phases
Identical SC and ISDW onsets
SC phase grows at the expense of ISDW phase
Chemical or Electronic origin?

17. Revisit LTT and ISDW Competing SC and ISDW, not LTT and ISDW LTT LTO
La2-xBa1/8CuO4
Non-SC
La2-xSrxCuO4+d SC
Structure ordering
LTT
LTO
Magnetic ordering
38K
3.5MHz
40K
Competing SC and ISDW, not LTT and ISDW
Luke et al, Physica C 1991

18. LTT and 1/8 dip of Tc

19. Why Electronic Phase Separation?
t-J model by Emery and Kivelson:
“Holes tend to phase separate but long-range Coulomb repulsion frustrates phase separation”
Competing AF correlation and Coulomb interaction
quantum confinement, paired electrons
Wigner crystal?
Löw, Emery, Fabricius, and
Kivelson, PRL 1994
Xiuqing Huang, cond-mat/

20. Summary and Conclusions
Large unexplored phase space
PS of electronic origin: indep. of x or d alone, identical ISDW phase, competing SC and static magnetic phases
Competing SC and ISDW, not SC and LTT
The electronic interaction of the doped holes is the primary driver of the phase separation rather than specific chemistry of O or Sr in this compound
Collaborators: Hashini Mohottala and Barry Wells (U. Conn.) et al, Nature Materials 2006

21. Wigner crystals
Phys. Rev. Lett. vol. 86, p (2001)

22. Stripes in La2-xSrxCuO4
Fujita et al, RRB 2002
Marouchkine, 2006

23. Staging behavior – neutron scattering
PHYSICAL REVIEW B 69, (2004)