Magnetic states of lightly hole

Magnetic states of lightly holedoped 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
Contents
• Introduction
High-Tc cuprate superconductors
• Measurement
muon spin rotation (μSR)
• Result
Phase diagram of YBa2Cu3O6+y
• Conclusion
Introduction
High-Tc Cuprate Superconductors
HgCaBaCuO
（under high pressure）
160
160
HgCaBaCuO
（under high pressure）
TlCaBaCuO
TlCaBaCuO
Tc (K)
BiCaSrCuO
100
100
80
HgCaBaCuO
Cuprate Superconductor
YBaCuO
liquid nitrogen
60
00
Hg
Pb NbC
Nb
1910
1911
NbN
V3Si
Nb3Sn
LaSrCuO
LaBaCuO
Nb3Ge
Nb-Al-Ge
1990
1986
(year)
Increase of Transition Temperature (Tc)
Introduction
High-Tc Cuprate Superconductors
La2CuO4
La3+→Ba2+
Cu(3d104s1)
d(x22-y
-y22))
3d(x
charge
reservoir
電荷供給層
3d(3z2-r2)
Cu+2
(3d9)
La (Ba)
CuO
CuO2 layer
面
La3+2-xBa2+xCuO4
3d(xy)
Cu2+x
3d(yz, zx)
charge
reservoir
電荷供給層
Cu
crystal structure
of La-Ba-Cu-O
La(Ba)
O
electric conductivity with hole doping
Superconductivity emerges with optimal doping.
Introduction
High-Tc Cuprate Superconductors
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.
sample
YBa2Cu3O6+y for various oxygen-content y
various hole density h
CuO-chain
CuO2 plane
T (K)
CuO2 plane
hole density
What is μSR (muon spin rotation) ?
Measurement
Property of Muon
• spin: I = ½
• gyromagnetic ratio: 135.53MHz/T
It’s very sensitive even to low magnetic field.
• mean lifetime: 2.2μs
pion mean lifetime: 26ns
What is μSR (muon spin rotation) ?
internal field
muon (μ+)
many muons
sample
positron
about
t μs later…
Measurement
detected!!
H
positron counter
• Internal field
Sμ
• The positron emission in the muon decay is asymmetric.
• Eech muon has different life.
Internal field is determined from time dependence of muon asymmetry.
Result
T (K)
μSR Result
h=0.02
hole density
h=0.04
only depend on muon’s life
Internal field is not static.
h=0.07
damped oscillation
static field
Temperature dependence of the moment
mh, T   2 D
TN
BAO h, T 
BAO (0)
m :magnetization
h :hole density
BAO :internal field at the apical oxygen
T (K)
Re-entrant
Thermally
activated
Result
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.
Thermally activated regime (high temperature) & Re-entrant regime (low temperature)
Activation temperature TA
hole doping
TA
hole dependence of TA
Result
extrapolation of
the m(h,T) power-law
Result
Phase diagram
AFM phase is separeted into two regimes.
• Re-entrant regime
Holes are localized.
Spins are freezing.
AFM
The moment recovers to 0.6μB.
Thermally
activated
Re-entrant
SC
• Thermally activated regime
Holes are delocalized.
AFM phase vanishes at
SC phase emerges at
QCP!!
Holes in CuO2 layer…
hole
spin
Holes are delocalized.
Holes are localized.
Spins are freezing.
Conclusion
• There are two distinct regimes in AFM phase.
Re-entrant and Thermally Activated
• 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.

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