Applied muon science: novel perspectives133.1.141.121/~nufact04_talks/talks/28_ple_morenzoni.pdf ·...

NuFact04 Osaka, Japan 27.07.2004 1

Applied muon science:novel perspectives

E. Morenzoni

Paul Scherrer InstituteCH-5232 Villigen PSI

Switzerland

2Paul Scherrer Institut • 5232 Villigen PSI Nufact2004-Osaka / 28.7.2004 / E. Morenzoni

Applied muon scienceMuons for non-particle physicists:

µ− : heavy electron ( mµ ≈ 200 me)µ+ : light proton (mµ ≈ 1/9 mp), Muonium (µ+ e-) hydrogen isotope

Many applications (see also WG4):

atomic/molecular physics: muonic atoms and molecules,Mu spectroscopy (muon mass, magnetic moment...)

nuclear physics: nuclear charge moments,muon catalized fusion, nuclear capture

condensed matter physics, material science, chemistry: muon spin rotation/ relaxation/ resonance, µSR

latest development:muons for nanoscience, polarized muons for investigations on nm scaleneeds intense polarized muon beams and would greatly benefit from further intensity and beam quality increase

Measurement of :

-parity violation-muon spin, g-factor, decay asymmetryand

first muon spin rotation spectrum


µSR: Muon Spin Rotation/Relaxation

P(t) 31 A

)n)t(PA(eNdt

)t(dNt

e

=

↑

⋅+= µ+ τ− rr

10

Implant and thermalize polarized muons in the sample (no loss of polarization,stop site: generally interstitial)

Observe time evolution of muon polarization via asymmetric muon decay: (positrons preferentially emitted along muon spin)

Positron intensity as a function of time after implantation:

θS

)cos31(1

d)(dN

e θ+∝Ω

θ+

:1P For =


µSR: Muon Spin Rotation/Relaxation

Time evolution of the polarization of the muon ensemble is characterizedby precession and/or depolarization/relaxationin the local magnetic fields (spins, moments, currents)

Static and dynamic properties of fieldsvery sensitive magnetic/spin probe: 10-3 – 10-4 µBtime window for fluctuations: 10-5 – 10-11 s

Distribution of fields with field distribution p(B):

Fourier transform of P(t) p(B)

loclocloc

locL

dB)tBcos()B(p)t(P

B :precession Larmor

ϕ+γ=

γ=ω

µ

µ

∫

locL Bµγ=ω


Range of muons in matter

nm

mm

µm

102

10

1

1

102

10

1104103102101

Cu

Ran

ge

Energy [keV]

bulk

thin films,multilayers..

Allow depth-dependent µSR investigations ( ~ 1 – 200 nm)

Extend the use of µSR to new objects of investigations

New magnetic/spin probe for thin films, multilayers, surface regions, buried layers,..

“Surface Muons” from π+

decay at rest ( ~ 4 MeV) generally used for condensed matter studiesfor bulk studies: no depth resolution


Laser Ionization of thermal Muonium

1S

2P

unbound

355nm

122.09nm (Mu)

Muonium

µ e+

4 MeVµ+

Thermalization+ diffusion

Mu

µ+

Tungsten foil2000 K

0.5 µm

122

nm

355

nm

µ+

(0.2 eV)e-

e-

µ+

µ+Mu

µ+ e-

122.09 nm(Lyman-α)

1S

2P

-13.6 eV

0 eV

Mu

355 nm

Courtesy of P. Bakule, RIKEN-RALP. Bakule, Y. Matsuda, K. Nagamine et al., RIKEN-RAL, KEK

Stop surface muons in hot W foil

Ionize thermal Mu diffusing from foil by pulsed operation (25 Hz) of speciallydeveloped laser systems

Timing determined by laser pulsing (8 ns),better than muon pulse width (100 ns)

Intrinsic energy spread 0.2 eV

Energy spread after accel. < 50 eV

Energy interval 1 –10 keV

Efficiency

Intensity ~ 15 µ+/sec

Polarization: 50%

Principally achievable efficiency: 1%Scalable to high intensity but technologicallydemanding

510−µ

≅ε∆

≅ε + ionMu

Rd

SiO2

×10

Energie [eV]0 25 50 75 100

10

20

30

40

50

Spek

trale

Dic

hte

[a.u

.]

1 10 102 103

Energy [keV]

Cou

nts

/(keV

10

)

9µ

20

40

60

1

MyoniumMuonium

Surface Muons

∼ 4 MeV∼ 100% polarized

∼100 µm ∼500 nms-Ne, Ar,s-N2

6 K

Generation of polarized epithermal muons by moderation

8D. Harshmann et al. 1987, E. M. 1992

Surface Muons

∼ 4 MeV∼ 100% polarized

∼100 µm ∼500 nms-Ne, Ar,s-N2

6 K

Mechanism of epithermal µ+ production in weakly bound insulators:

-Suppression of electronic energy losses-Soft elastic collisions in the eV region

escape before thermalization E. Morenzoni, F. Kottmann, D. Maden, B. Matthias, M. Meyberg, Th. Prokscha, Th. Wutzke, U. Zimmermann, Phys.Rev.Lett. 72, 2793 (1994).

Characteristics of epithermal muons

9

Time [ s]µ

Asy

mm

etry

Polarization: ~ 100%

AP

(t)

LE-muons source:

100% polarized peak energy: ∼ 15 ± 10 eVmoderation efficiency ∼ 10-4

escape depth : 15-100 nmangular distribution: dN ∼ cosθdΩ

R

d

∆≅ε

+

+µ

µ

• UHV:p ∼ 10-10 mbar

• Electrostaticaccel-decel and transport system (LN2 cooled)

10

Very low energy µ+ beam and set-up forLE-µSR

Very low energy µ+ beam and set-up forLE-µSR

11

~2.5 •107 µ+/s

~3000 µ+/s

~1000 µ+/s

Polarized Low EnergyMuon Beam (Tertiary DC beam)∼0.5-30 keV(∼1 – 200 nm)Energy uncertainty: 400 eV


Experimental program: main topicsMagnetism

Interlayer exchange coupling in multilayers, superparamagnetism in mass selected nanoclusters, Magnetic ordering in buried, strained/stressed films, surface vs bulk magnetism in LaCoO3

Superconductivity (near surface)Non-local effects, Isotope effects, Vortex motion and pattern formation in 2D

Interplay/Coexistence Magnetism/SuperconductivityYBCO/SRO superlattices, Fe/Pb multilayers, YBCO/PBCO/YBCO multilayers, Spin glass transition /sc in LSCO meanderfilms, Surface magnetism/superconductivity in La1.9Ce0.1CuO4, search for spontaneous magnetization at the surface of YBCO110

Dimensional or surface effectsSurface polymer dynamics, Finite size effects in spin glass freezing,Surface vs bulk magnetism in LaCoO3

Hydrogen states and dynamics in semiconductors and dieletricsLow k-materials (nanoporous silica), hydrogen states in semiconductor and insulating films

Basics of LE-µSRImplantation studies, behavior at surfaces, diffusion at interfaces, muon moderation studies

B(z) superconductor

z

muon implantation profile for a particularmuon energy Eµ

n(z,Eµ)

µSR experiment ⇒magnetic field probability distribution p(B) sensed by the muons

n(z)dz = p(B)dB ⇒ B(z)n(z)dz = p(B)dB ⇒ B(z)

♦

♦

♦

♦

♦♦

Depth dependent µSR measurements in near surface regions

Bext

0

λ

magnetic field profile B(z)Characteristic lengths of the sc λ, ξ


Magnetic Field Profiles in Pb and YBa2Cu3O7-δ

0 50 100 150

1E-3

0.01YBa2Cu3O7-δ, T=20K, Tc=87.5K

hext

= 91.5(3) G, ξ0 = 1.5 nm fixed, λ0 = 137(10) nm

hext exp(-z/λ(T)) 3.4 keV 8.9 keV 15.9 keV 20.9 keV 29.4 keV

B (T

)z (nm)0 50 100 150

1E-3

0.01

0 50 100 150

1E-3

0.01

0 50 100 150

1E-3

0.01Lead, Tc=7.0(2) K, hext = 91.5(3)G,

ξ0 = 90(5)nm, λ0 = 58(3)nm

6.66K

6.19K

2.85K

z (nm)

B (T

)

κ0 = 0.64(5) κ0 ≈ 90

non-local non- exponential local exponentialA. Suter, E. Morenzoni, R. Khasanov, H. Luetkens, T. Prokscha, and N. Garifianov Phys. Rev. Lett. 92, 087001 (2004).

Magnetic field profiles beneaththe surface with a few nm resolution

ξ

ξ

λ

0

z

“local”

“non-local”

)T(z

0abeB)z(B λ

−=→

Direct Test of theories (London, BCS)

)T(nm)T(s

*∝λ

Local, non-local response

Determination of the coherence length

Direct, absolute measurement of magnetic penetration depth

effective mass density of

supercarriers

700

600

500

400

300

200

1000 10 20 30 40 50 60 70 80 90

Thin Film (Meissner state) Thin Film (mixed state) Single crystal (mixed state, Sonier et al., PRL (1994) 744)72

Temperature [K]

λ ab(T

) [nm

]

T.J. Jackson, T.M. Riseman, E.M. Forgan, H. Glückler, T. Prokscha, E. Morenzoni, M. Pleines, Ch. Niedermayer, G. Schatz, H. Luetkens, and J. Litterst, Phys. Rev. Lett. 84, 4958 (2000).



Isotope effects in YBa2Cu3O7-δ

0 10 20 30 40 50

0.0

0.5

1.0

-0.10

-0.05

0.00

(a)

σ sc (µ

s-1)

T(K)

16Opac

18Opac

16Op18Oac

18Op16Oac

(b)

σ sc(T

) - σ

fit(T

)(16

0)

cba

CuO Chain

Apical Oxygen

CuO2 Plane

O(2,3)

Cu(2)

O(4)

Cu(1)O(1)

Ba

Y

16O

18O

YBa2Cu3O7-δ Film

Oxygen isotope effect on the magnetic penetration depth.

Which Oxygen in the crystal lattice mainly contributes to the effect?

Selective site substitution

Y0.6Pr0.4Ba2Cu3O7-δ Powder

Bulk-µSR measurements show that the substitution of 16O Atoms in the CuO2 plane is responsible for the effect.

Structure of YBa2Cu3O7-δ

21λ

∝σ

R. Khasanov, D.G. Eshchenko, H. Luetkens, E. Morenzoni, T. Prokscha, A. Suter, N. Garifianov,M. Mali, J. Roos, K. Conder, and H. Keller Phys. Rev. Lett. 92, 057602 (2004)

0 % .

nn

mm % .

s

s

ab

ab

ab

ab

≅⇓⇓

⎟⎟⎠

⎞⎜⎜⎝

⎛ ∆−

∆=

λλ∆

=

65

2182

dB Φ)Btcos(p(B)(t)P µx ∫ +γ=

Flux line lattice field distribution across the surface

π2/a

Near surface region of a Type II superconductor in the vortex state

18

Ch. Niedermayer, E.M. Forgan, H. Glückler, A. Hofer, E. Morenzoni, M. Pleines, T. Prokscha, T.M. Riseman, M. Birke, T.J. Jackson, J. Litterst, M.W. Long, H. Luetkens, A. Schatz, and G. Schatz, Phys.Rev.Lett. 83, 3932-3935 (1999).


Magnetic Multilayers (ML)

Normal Metal FerromagnetFerromagnet

Interlayer exchange coupling in magnetic ML

IEC oscillates with spacer thickness(RKKY)

Different techniques to probe the FM layer (polarization of secondary electrons, MOKE, …)

oscillation period, coupling strength

Muons can locally probe the polarization of the nonmagnetic spacer mediating the coupling

20

M1 M2d

4nm 20nm 4nm

Fe/Ag/FeImplantation profile (3 keV)

Oscillating polarization of conduction electrons

∑=

⊥ θ+=2

1

1

ii

ini )xqsin(

xC)x(B

i

Polarisation of conduction electrons

Oscillating magnetic field in Ag

B(x) and IEC oscillate

with the same period but

attenuation with distance

from interface different !

H. Luetkens, J. Korecki, E. Morenzoni, T. Prokscha, M. Birke, H. Glückler, R. Khasanov, H.-H. Klauss, T. Slezak, A. Suter, E. M. Forgan, Ch. Niedermayer, and F. J. Litterst Phys Rev. Lett. 91, 017204 (2003).


Magnetism/Superconductivity in ML

Superconductor FerromagnetFerromagnet


Superconducting and magnetic orderingCompare data above and below Tc

T<TcT>Tc

Pb 215 nm

Fe 2,6 nmMo 6 nm

Fe 2,8 nm

A. Drew, S. Lee et al: St. Andrews-PSI-Leeds collaboration

Spin Density Wave in Pb induced above and belowTc with same wave vectors but phase shifts by 900

below Tc

Tolerance (coexistence) and Interaction betweenthe magnetic and superconducting order in the PbfilmWeaker attenuation of electron polarization thanexpected∑ φ+

=∝i

nii

i ix)xksin(A B(x) )x(M

Oscillating polarisation of conducting/superconductingelectrons

New high-intensity surface muon beamfor LE-µ+ applications

24

Replaced withnew beam in 2004

used up to now for thin films studies

Target E: 60 mm graphite

proton beam

Installation/ Commissioning

2003/2004

Intensity increase: 7

Parameters of the new surface muon beam

T. Prokscha∼ 7000 eV-keV µ+/sec 25


Conclusions and outlook

Polarized low energy muons (eV-keV) can be used as a tool for depth resolved investigations of single- and multilayered samples over distances of the order ~ 1 - 200 nm. Applications in superconductivity, magnetism, soft matter, semiconductors...The new surface muon beam line and the present upgrade at PSI will improve the exploitation of the potential of this technique.High quality muon beams (flux, emittance, brillance) would have great impact on the application of muons in nanoscience (e.g. microbeam, possibility of lateral resolution on µm scale, investigation of ~100 µm x 100 µm samples).

N. GarifianovH. Luetkens

T. Prokscha

E. MH.P. Weber

A. SuterR. Khasanov

27


Also thanks tofor selected experiments and samples:

University of Birmingham: E. Forgan, T. Jackson, T. Riseman

Technische Universität Braunschweig: M. Birke, J. Litterst

Universität Konstanz: C. Niedermayer

Universität Zürich: H. Keller

Academy of Mining and Metallurgy, Krakau: J. Korecki, T. Slezak

Paul Scherrer Institute: K. Conder, M. Horisberger

for the construction of the new surface muon beam line :

Paul Scherrer Institute: R. Kobler, K. Deiters, D. George, S. May

and the PSI technical divisions

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