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Magnetic states of lightly hole-doped cuprates in the clean limit as
seen via zero-field muon spin spectroscopy
Kitaoka LabKaneda Takuya
F. Coneri, S. Sanna, K. Zheng, J. Lord, and R. De Renzi, Phy. Rev. B 81, 104507 (2010)
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Contents
• IntroductionHigh-Tc cuprate superconductors
• Measurementmuon spin rotation (μSR)
• ResultPhase diagram of YBa2Cu3O6+y
• Conclusion
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1910 19900
60
80
100
160
LaSrCuO
YBaCuO
BiCaSrCuO
TlCaBaCuOHgCaBaCuOTlCaBaCuO
HgCaBaCuO( under high pressur
e )
HgCaBaCuO( under high pressure )
NbNbC
V3SiNbN
Nb3SnPb
Nb3Ge
Nb-Al-Ge
liquid nitrogen
Hg
1911 1986
0
100
160
LaBaCuO
Tc (K)
(year)
Increase of Transition Temperature (Tc)
Cuprate Superconductor
High-Tc Cuprate Superconductors Introduction
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crystal structureof La-Ba-Cu-O
La3+2-xBa2+
xCuO4
Cu2+x
CuO2 面
電荷供給層
電荷供給層
La (Ba)
electric conductivity with hole doping
Superconductivity emerges with optimal doping.
Cu
O
La(Ba)
High-Tc Cuprate Superconductors Introduction
charge reservoir
CuO2 layer
charge reservoir
La2CuO4
d(x2-y2)
Cu+2
(3d9)
3d(x2-y2)Cu(3d104s1)
3d(3z2-r2)
3d(xy)
3d(yz, zx)
La3+→Ba2+
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In order to understand the ground state of cuprate superconductor, careful study about its underdoped region is required.
High-Tc Cuprate Superconductors Introduction
AFM
SCSC
AFM
charge reservoir
CuO2 layer
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sample
YBa2Cu3O6+y for various oxygen-content y
various hole density h
CuO-chain
CuO2 plane
CuO2 plane
hole density
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• spin: I = ½• gyromagnetic ratio: 135.53MHz/T
• mean lifetime: 2.2μs
What is μSR (muon spin rotation) ? Measurement
Property of Muon
It’s very sensitive even to low magnetic field.
pion mean lifetime: 26ns
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sample
internal field
positron counter
muon (μ+)
positron
• Internal field
about t μs later…
Internal field is determined from time dependence of muon asymmetry.
What is μSR (muon spin rotation) ? Measurement
H
Sμ
detected!!
• The positron emission in the muon decay is asymmetric.
many muons
• Eech muon has different life.
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μSR Result Result
h=0.02
h=0.04
h=0.07
hole density
only depend on muon’s life
damped oscillationstatic field
Internal field is not static.
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TN
hole density
• TN drop rapidly with increasing the hole density h.
• For h =0.035, m(h,T) deviates from power-law behavior (dashed line) and an upturn (solid line) appears.
)0(
,, 2
AOB
ThBThm AO
D
m :magnetizationh :hole densityBAO :internal field at the apical oxygen
Temperature dependence of the moment Result
Thermally activated regime (high temperature) & Re-entrant regime (low temperature)
Thermally activated
Re-entrant
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Activation temperature TAResult
TA
hole dependence of TA
extrapolation of the m(h,T) power-law
hole dopinghole doping
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Phase diagram Result
AFM
SCRe-entrant
Thermallyactivated
• Re-entrant regime Holes are localized.
Spins are freezing.
The moment recovers to 0.6μB.
• Thermally activated regimeHoles are delocalized.
AFM phase is separeted into two regimes.
AFM phase vanishes atSC phase emerges at
QCP!!
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hole spin
Holes in CuO2 layer…
Holes are localized.Spins are freezing. Holes are delocalized.
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• There are two distinct regimes in AFM phase.
• In re-entrant regime holes are localized and spins are freezing.
• The critical hole density hc and hs have the same value. And the value h = 0.056 is a quantum critical point (QCP) for the cuprate clean limit.
Conclusion
Re-entrant and Thermally Activated