Magnetic states of lightly hole-doped cuprates in the clean limit as seen via zero-field muon spin spectroscopy

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Magnetic states of lightly hole-doped cuprates in
the clean limit as seen via zero-field muon spin
spectroscopy
F. Coneri, S. Sanna, K. Zheng, J. Lord, and R. De
Renzi, Phy. Rev. B 81, 104507 (2010)

• Kitaoka Lab
• Kaneda Takuya

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Contents

• Introduction
• High-Tc cuprate superconductors
• Measurement
• muon spin rotation (µSR)
• Result
• Phase diagram of YBa2Cu3O6y
• Conclusion

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High-Tc Cuprate Superconductors
Introduction
Increase of Transition Temperature (Tc)
4
High-Tc Cuprate Superconductors
Introduction
La3?Ba2
charge reservoir
CuO2 layer
La (Ba)
charge reservoir
Cu
crystal structure of La-Ba-Cu-O
O
La(Ba)
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High-Tc Cuprate Superconductors
Introduction
charge reservoir
CuO2 layer
AFM
AFM
SC
SC
In order to understand the ground state of
cuprate superconductor, careful study about its
underdoped region is required.
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sample

• YBa2Cu3O6y for various oxygen-content y
• various hole density h

CuO-chain
CuO2 plane
T (K)
CuO2 plane
hole density
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What is µSR (muon spin rotation) ?
Measurement
Property of Muon

• spin I ½
• gyromagnetic ratio 135.53MHz/T
• mean lifetime 2.2µs

 
Its very sensitive even to low magnetic field.
 
pion mean lifetime 26ns
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What is µSR (muon spin rotation) ?
Measurement
internal field
sample
muon (µ)
about t µs later
positron counter
 

• Internal field

• The positron emission in the muon decay is
  asymmetric.

• Eech muon has different life.

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µSR Result
Result
h0.02
h0.04
 
only depend on muons life
 
Internal field is not static.
h0.07
 
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Temperature dependence of the moment
Result
Re-entrant
Thermally activated

• 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.

Thermally activated regime (high temperature)
Re-entrant regime (low temperature)
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Activation temperature TA
Result
 
hole doping
extrapolation of the m(h,T) power-law
TA
hole dependence of TA
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Phase diagram
Result
AFM phase is separeted into two regimes.

• Re-entrant regime
• Holes are localized.
• Spins are freezing.
• The moment recovers to 0.6µB.
• Thermally activated regime
• Holes are delocalized.

AFM
Thermally activated
SC
Re-entrant
AFM phase vanishes at SC phase emerges at
 
 
QCP!!
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Holes in CuO2 layer
 
 
hole
spin
Holes are localized. Spins are freezing.
Holes are delocalized.
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Conclusion

• 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.

Re-entrant and Thermally Activated
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Solving the degeneracy of 3d-orbital
Appendix
?????
?????
x2-y2
x2-y2, 3z2-r2
3z2-r2
3d
xy
xy, yz, zx
yz, zx
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Magnetic volume fraction
Appendix
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Power-law
Appendix
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Equations
Appendix
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Equations
Appendix