Transcript Phase Separation in La2

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
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Inhomogeneous Electron Density
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CDW, Dimerization and Nesting
1d Peierls instability : q = 2kF
CDW => MIT
2d Fermi Surface nesting
Peierls Transition
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Phase Diagrams
La2CuO4+d
La2-xSrxCuO4
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Charge Inhomogeneity: Spin and charge stripes
La2-x-yNdySrxCuO4
•Holes segregate into AF
antiphase domain walls
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Tranquada et al, Nature 1995
Spin/Charge Stripes and Superconductivity
Yamada et al, PRB 1998
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1d domain walls in low x La2-xSrxCuO4
L ~ 1/x
Finite size effect:
1-TN(x)/TN(0) ~ L-1/n
Cho et al, 1993
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Charge Inhomogeneity: Checkerboard Type
Underdoped Ca2-xNaxCuO2Cl2
Hanaguri et al, Nature 2004
Underdoped
Bi2Sr2CaCu2O8+d
Hashimoto et al, PRB 2006
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Electrochemical oxygen intercalation
La2CuO4+d
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Reference
La2CuO4
Grenier et al, Physica C 1991
Pt
NaOH/H2O electrolyte
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Li et al, PRL 1996
Macroscopic Phase Separation in La2CuO4+d
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
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Spinodal Decomposition
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Staging: charge/oxygen segregation
La2CuO4
+d
Wells et al, Science 1997
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Electrochemical oxygen intercalation
La2CuO4+d
La2-xSrxCuO4
V
Reference
La2CuO4
Grenier et al, Physica C 1991
Pt
NaOH/H2O electrolyte
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La2-xSrxCuO4+d: hole doping through Srx and Od
• Identical SC
onset ~40K
• SC volume
fraction indep. of x
or d
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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
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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
La2-xBa1/8CuO4
Non-SC
La2-xSrxCuO4+d
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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Luke et al, Physica C 1991
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
•quantum confinement, paired
electrons
•Wigner crystal?
Löw, Emery, Fabricius, and
Kivelson, PRL 1994
Xiuqing Huang, cond-mat/0606177
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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
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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 22
Staging behavior – neutron scattering
PHYSICAL REVIEW B
69, 020502 (2004)
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