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)

Contents

• IntroductionHigh-Tc cuprate superconductors

• Measurementmuon spin rotation (μSR)

• ResultPhase diagram of YBa2Cu3O6+y

• Conclusion

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

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+

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

sample

YBa2Cu3O6+y for various oxygen-content y

various hole density h

CuO-chain

CuO2 plane

CuO2 plane

hole density

• 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

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.

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.

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

Activation temperature TAResult

TA

hole dependence of TA

extrapolation of the m(h,T) power-law

hole dopinghole doping

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!!

hole spin

Holes in CuO2 layer…

Holes are localized.Spins are freezing. Holes are delocalized.

• 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