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Charge Inhomogeneity and Electronic Phase Separation in Layered Cuprate

F. C. ChouCenter for Condensed Matter Sciences, National Taiwan UniversityNational Synchrotron Radiation Research Center, Taiwan

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Inhomogeneous Electron Density

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CDW, Dimerization and Nesting

Peierls Transition

1d Peierls instability : q = 2kF

CDW => MIT

2d Fermi Surface nesting

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Phase DiagramsLa2CuO4+ La2-xSrxCuO4

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Charge Inhomogeneity: Spin and charge stripes

Tranquada et al, Nature 1995

•Holes segregate into AF antiphase domain walls

La2-x-yNdySrxCuO4

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Spin/Charge Stripes and Superconductivity

Yamada et al, PRB 1998

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1d domain walls in low x La2-xSrxCuO4

Cho et al, 1993

L ~ 1/x

1-TN(x)/TN(0) ~ L-1/

Finite size effect:

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Charge Inhomogeneity: Checkerboard Type

Hanaguri et al, Nature 2004

Underdoped Ca2-xNaxCuO2Cl2Underdoped Bi2Sr2CaCu2O8+

Hashimoto et al, PRB 2006

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Electrochemical oxygen intercalation

Grenier et al, Physica C 1991 Li et al, PRL 1996

La2CuO4+

La2CuO4

ReferencePt

NaOH/H2O electrolyte

V

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Macroscopic Phase Separation in La2CuO4+

Radaelli et al, PRB 1993; Statt et al, PRB 1995

• Electrochemical oxygen intercalation• Undoped AF domain and hope-doped SC domain

La2CuO4+

La2-xSrxCuO4

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Spinodal Decomposition

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Staging: charge/oxygen segregation

Wells et al, Science 1997

La2CuO4

+

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Electrochemical oxygen intercalation

Grenier et al, Physica C 1991

La2CuO4

ReferencePt

NaOH/H2O electrolyte

V

La2CuO4+ La2-xSrxCuO4

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La2-xSrxCuO4+: hole doping through Srx and O

• Identical SC onset ~40K

• SC volume fraction indep. of x or

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La2-xSrxCuO4+: magnetic phase by ZF-SRLa1.91Sr0.09CuO4+

• Magnetic static ordering onset near ~40K

• Magnetic volume fraction independent of x or

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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?

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Revisit LTT and ISDW

Luke et al, Physica C 1991

La2-xBa1/8CuO4

Non-SC

La2-xSrxCuO4+

SC

Structure ordering

LTT LTO

Magnetic ordering

38K

3.5MHz

40K

3.5MHz

• Competing SC and ISDW, not LTT and ISDW

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LTT and 1/8 dip of Tc

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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

Löw, Emery, Fabricius, andKivelson, PRL 1994 Xiuqing Huang, cond-mat/060617

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•quantum confinement, paired electrons•Wigner crystal?

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Summary and Conclusions

• Large unexplored phase space• PS of electronic origin: indep. of x or 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

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Wigner crystals

Phys. Rev. Lett. vol. 86, p. 3851 (2001)

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Stripes in La2-xSrxCuO4

Fujita et al, RRB 2002 Marouchkine, 2006

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Staging behavior – neutron scattering

PHYSICAL REVIEW B 69, 020502 (2004)