Fast and Slow Muons at PSIPaul Scherrer Institut • 5232 Villigen PSI Isis Muon Training Course/...

Paul Scherrer Institut • 5232 Villigen PSI Isis Muon Training Course / 25th-Feb-2005 / T. Prokscha

PAUL SCHERRER INSTITUT

Fast and Slow Muons at PSI

Thomas Prokscha

Laboratory for Muon Spin SpectroscopyPaul Scherrer InsitutCH-5232 Villigen PSI

Switzerland

Isis Muon Training Course, 21th – 25th February 2005

RAL/ISIS

γ SLS

Aareµ SµSn SINQ

SµS and SINQ

50 MHz proton cyclotron, 2mA,600 MeV

ð quasi-continuous muon andneutron beams

most powerful proton cyloctronworldwidemost intense muon beams

unique low-energy (0.5-30keV)muon beam

At PSI:∼1016 protons / sec @ 600 MeV (ð 1 MW power on 5x5mm2,40kW/mm2, Fe melts in 0.1ms,electric power demand of 3000 appartments)

∼ 107- 108 µ+/sec, 100 % pol., ∼ 4 MeV

PAUL SCHERRER INSTITUT50 MHz beam

PAUL SCHERRER INSTITUTContinuous muon beam experiment

Myon-Counter Positron-

Counter

e+sµ pµ

P(t)P(t=0)

SamplePositron-Counter

ω = γ Β γµ µ µ µ( = 135.5 MHz/T)·

Ø time resolution = 1 ns

Ø fast relaxation observable( > 10 µs-1)

Ø no segmentation/positioninformation for e+ necessary

Ø start counter needed

Ø random background (can bereduced by MORE)

Ø limited time window

Ø separator required for surface muons

continuous ïð pulsed

A(σt) = A0 x exp(-ω2σt2/2)

decay channel, µ+ and µ-E = 15 – 60 MeV

surface muon beam, µ+E = 0.1 – 4.2 MeV

reconstruction 2004

ALC, LEM, until 2003

LEM 2005

low-energy µ+ (LEM)0.5 – 30 keV

Muon beams at PSI

Decay and surface muons

Jess Brewer, UBC & TRIUMF:

PAUL SCHERRER INSTITUTµSR instruments at PSI

Ø GPS: General Purpose Surface muon instrument; permanent installation;πM3 beam shared with LTF; 4 MeV µ+, Separator/Spin Rotator ( 6 – 60o);0 – 0.6 T, 1.8 – 300 K; Muons on Request ( MORE)

Ø LTF: Low Temperature Facility; permanent installation; πM3 beamshared with GPS; 0 – 3 T, 0.01 K – 4.2 K; MORE

Ø Dolly: GPS „clone“; πE1 or πE3 beam, new Spin Rotator

Ø GPD: General Purpose Decay channel instrument; µE1 beam; 15 – 60 MeVµ+ and µ-; 0 – 0.5 T, 0.3 – 400 K; high pressure < 15 kbar

Ø ALC: Avoided Level Crossing instrument; πE3 beam; 4 MeV µ+;Separator; 0 – 5 T, 4 – 600 K; integral counting

Ø LEM: Low Energy Muon beam & µSR instrument; πE3 beam (new µE4 beamunder commisioning); 0 – 30 keV µ+ ( controllable implantation depth 0 – 300 nm)0 – 0.3 T, 2.2 – 700 K

General Purpose Surface muon instrument

Muons On Request(MORE)

Ø GPS “tells” Kicker to send a muon toGPS

Ø If a muon is detected in GPS “tell”Kicker to send the beam to LTF

Ø no random beam background in GPS

Ø if decay e+ is detected in GPS the next muon is requested from theKicker

MORE II:

MORE in UPt3

• Two Knight shift components

• Dramatic and opposite Tdependence around TN (6K)

• UPt3 is intrinsically inhomogenous

A. Yaouanc et al, PRL84, 2702 (2000).

MORE: Condon domains in Sn

G.Solt, V.S.Egorov, Physica B318, 2002 G.Solt, V.S.Egorov et al., Phys.Rev.B62, 2000

ν1 = 353.17 MHz ν2 = 353.25 MHz∆ν = 80 kHz !

need good time resolutionand small background

ð MORE

Condon domains are manifestations ofthe collective behaviour of electronsin quantized cyclotron orbits (Landau states)

MORE: Condon domains in Be

G.Solt, V.S.Egorov et al., PSI, 2002

ν1 = 356.93 MHz ν2 = 357.32 MHz∆ν = 390 kHz !

PAUL SCHERRER INSTITUTVortex state of a superconductor

inside the solid:

Scanning

Tunneling

Microscop

Decoration

surface:

YBa2Cu3O6.95

T=10 K, Bext=0.1 T

-100 -50 50 100 0

B-Bext[G]

OsO6octahedra

•Superconductivity in the pyrochlore related oxide RbOs2O6R. Khasanov et al., PRL 93, 157004 (2004)

– Novel superconductor recently discovered RbOs2O6 Tc = 6.3KHiroi et al. cond-matt/0402006

– From macroscopic measurements:controversy about type of superconductivityà BCS conventional ?à Unconventional (p-or d-wave) ?

ÆBulk µSR studies provide a direct measure of the field penetration depth λ(T) àcritical test for typeof superconductivity à weakly coupled s-wave BCS!

Opposite to the situation observed for NaxCoO2 • yH2O (ISIS+PSI)A. Kanigel et al., PRL 92, 257007 (2004)

Examples of µSR Research at PSI

need to measure up to 2.5T ð νµ = 340 MHz(Hc2 = 5.7T)

PAUL SCHERRER INSTITUTExamples of µSR Research at PSI

• Evidence of Two LengthScalesin Mg1-xAlxB2 from µSR

S. Serventi et al., PRL 93, 217003 (2004)

– Effect of the two gaps on the internal fielddistribution in the fluxlattice state

– Determine two coherencelength parameters

PAUL SCHERRER INSTITUTExamples of µSR Research at PSI

• Measuring the quadrupolar order parameter by µSR – A. Schenck et al., PRL 93, 257601 (2004)– CeB6 (TN = 2.3K and TQ = 3.2K)– Fermi contact hyperfine contribution to the µ+-Knight shift

Acon ∼ quadrupolar order parameter determined from resonant and nonresonant x-ray scattering.

– RKKY induced conduction electron spin polarization depends on theorientation and expectation value of the ordered 4f quadrupole moments.

had to measure Knight shift up to 2.5T( ð νµ = 340 MHz)to gain new insight

formation of ≈100% polarised spin label by Mu addition to an unsaturated chemical bond:

3 spin-½ system: µ, p, eFermi contact interaction (electron spin density at muon/proton)+ magnetic dipole interaction muon/proton – electron

avoided crossings of magnetic energy levels at high magnetic fields ( ≈2T)⇒ dips in the field-dependence of the µ spin polarisation: ÷ longitudinal field relaxometry: spin-spin cross relaxation

Avoided Level Crossing (ALC)

hfc tensor: fixed orientation with respect to the radical

⇒ study of reorientational dynamics

Longitudinal magnetic field:

| α β β >

| α β α >| α α β >

| α α α >

|∆M| = 2

muon-proton

spin flip-flip

|∆M| = 1

muon spin flip

∆M = 0

muon-proton

spin flip-flop

| e µ p >

avoided level crossings: mixing of eigenstates

⇒ time evolution of the µ+ spin polarization

loss of observed FW-BW asymmetry

M = me + m1 + mp

spin-spin cross relaxation

advantages:

• long Mu precursor lifetime (up to 1 µs) - phase coherence lost in TF after 0.1 ns

• low concentrations of tracer molecules, Mu addition within τµ- TF requires ≥ 100 mM for diffusion controlled Mu addition

surfactant bilayers separated by water

phase transition Tαβ ≈ 50 °C (DSC)T > Tαβ: Lα - alkyl chains ‚fluid‘T < Tαβ: Lβ - more ordered packing of hydrocarbon

chains

lamellar phase:

H2C O C

H3CH3C

C16H33

DHTAC: cationic dichain surfactant

H2CCH2

cosurfactant: 2-phenylethanol(‘perfume’: essence of roses)

partitioning (local environment) of cosurfactants in lamellar phases

40 mM 2-phenylethanol in 15% DHTAC dispersion

18000 20000 22000

∆0∆1

25 °C

35 °C

45 °C

55 °C

65 °C

75 °C

magnetic field [G]

∆1 resonances only above Tαβ: residual anisotropy! PEA-Mu axially aligned within bilayer lineshape: dynamical averaging

∆0: discontinuity in Bres(T) at Tαβ: change of local environment!

20 30 40 50 60 70 80

ortho-∆ 0

para-∆ 0

meta-∆ 0

T [°C]

tracer in water in bilayer(but not static!)

3 isomers:

PAUL SCHERRER INSTITUTRange of muons in matter

1104103102101

Energy [keV]

bulkthin films,multilayers..

§Allows depth-dependent µSR investigations ( ~ 1 – 300 nm)

§Extend the use of µSR to new objects of investigtions

§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

PAUL SCHERRER INSTITUTImplantation profiles of LE-µ

0 5 10 15 20 25 30 350

200RangeVariance

0 50 100 150 200

29.4 keV

24.9 keV20.9 keV

15.9 keV

6.9 keV

3.4 keV

Depth [nm]

Energy [keV]

YBa2Cu3O7

depth sensitive,microscopic,magnetic and spin probe

thin films, near surface regions, multi-layers, buried layers, nano cluster

(stopping profile calculated with Monte Carlo

code Trim.SP by W. Eckstein, MPI Garching,

Germany; see E.Morenzoni et al., NIM B192

(2002))

PAUL SCHERRER INSTITUTMuon moderation

1 10 102 103

Energy [keV]

Counts

Myonium

∼100 µm

surface muons ∼ 4 MeV∼ 100% polarised

∼300 nm s-Ne, s-Ar,... s-N26 K

∼100 µm

T. Prokscha et al, PRA 58, 3739 (1998)

Epithermische Myonen

[eV]0 25 50 75 100

Energie Energie(known as good positron moderators)

PAUL SCHERRER INSTITUTMuon moderation II

surface muons∼ 4 MeV∼ 100% polarised

∼100 µm ∼300 nm s-Ne, s-Ars-N2

Time [ s]µ

Source of ∼ 15 eV 100% polarised muons

Mechanism:Suppression of energy lossdue to electronic excitationsin eV region in soft, perfectinsulators

Conversion efficiency: ∼10- 4

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

PAUL SCHERRER INSTITUTThe PSI LEM beam

~3•107 µ+/s

~2800 µ+/s, Ne/N2

~1600 µ+/s, Ar/N2

~750 µ+/s, Ne @ 12kV

~670 µ+/s, Ar @ 20 kV

Polarized Low Energy Muon Beam ∼ 0.5-30 keV

PAUL SCHERRER INSTITUTDepth dependent LE-µSR studies

B(z) superconductor

àmagnetic field profile B(z)àCharacteristic lengths of the sc λ, ξ

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)

♦♦♦♦

PAUL SCHERRER INSTITUTMagnetic field profiles in superconductors

“local”

“non-local”

nonlocallocal

0abeB)z(B λ

−=→

à Direct Test of theories (London, BCS)

*∝λ

à Direct, absolute measurement of magnetic penetration depth

ßeffective massßdensity of supercarriers

à Local, non-local response

à Determination of the coherence length ξ, and κ = λ/ξ

PAUL SCHERRER INSTITUTMagnetic field profiles in Pb and YBa2Cu3O7-δ

A. Suter, E. Morenzoni, R. Khasanov, H. Luetkens, T. Prokscha, andN. Garifianov, Phys. Rev. Lett. 92, 087001 (2004).

0 50 100 150

0.01YBa

7-δ, T=20K, T

c=87.5K

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

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

)z (nm)

0 50 100 150

0.01Lead, T

c=7.0(2) K, h

ext = 91.5(3)G,

ξ0 = 90(5)nm, λ

0 = 58(3)nm

z (nm)

κ0 = 0.64(5) κ0 ≈ 90

non-local ßànon- exponential local ßà exponential

PAUL SCHERRER INSTITUTMagnetic field profile in YBa2Cu3O7-δ

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

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).

0abeB)z(B λ

−=→

Direct, absolute measurementof magnetic penetration depth

Field profile: B(z,T)

)T(n)e(m

ab 20 2µ

Vortices near surfaceYBa2Cu3O7-d film in vortex state:

Flux line lattice magnetic field distribution across the surface

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).

LE-muons in multi-layers

Fit-Function:

Free fit parameters:

Multi-layered samples:

-magnetic/non magnetic

-superconducting/ magnetic

-superconducting/ nonsuperconducting

4nm 20nm 4nm

Fe/Ag/Feimplantation profile (3 keV)

LE-muons in Ag/Fe/Ag

Observation of the spatially oscillating spin density in Ag !

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).

B(x) and IEC oscillate

with the same period but

attenuation with distance

from interface different !

PAUL SCHERRER INSTITUTSuperconducting and magnetic ordering in

Fe/Pb/FeCompare data above and below Tc

T<TcT>Tc

∑ φ+=∝i

i ix)xksin(

A B(x) )x(M

Oscillating polarisation of conducting/superconductingàelectrons

Pb 215 nm

Fe 2,6 nmMo 6 nm

Fe 2,8 nm

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

below Tc

uTolerance (coexistence) and Interaction betweenthe magnetic and superconducting order in the PbfilmuWeaker attenuation of electron polarization than

expected

A. Drew, S. Lee et al: St. Andrews-PSI-Leeds collaborationSubmitted to PRL

Muon developments and projects at PSI

Ø reconstructed, dedicated µE4 beamline for LEM, 5000/secLE-µ+ on sample, 2005; upgrade of LEM apparatus

Ø high-field µSR instrument, up to 15 T (νµ = 2 GHz)

Ø detector development, fast timing, position information

Ø change of DAQ system to MIDAS, new data format (Nexus)

Ø new VME based DAQ hardware, new progammable VME CFD

Ø GPD upgrade: new magnet (0-6.5kG), new cryostat (0.3-300K), new detectors

Ø active zero field compensation

PAUL SCHERRER INSTITUTµE4/LEM beam area

new LEM beam and LE-µSR spectrometer

Electrostatic (ExB) separator

new µE4 area

Status of LEM- and µE4-reconstruction,Feb-2005

µSR worldwide

PSI: continuous, the most intense muon beams, MORE, unique LEM beam

TRIUMF: continuous (Vancouver, Kanada)

ISIS: most intense pulsed muon source (near Oxford, Great Britain)

KEK: pulsed (Tsukuba, Japan); JAERI/KEK J-Parc project at Tokai: 3 GeV/333µA pulsed beam, 25Hz, 80-100ns bunches, 2009

JINR: pulsed (Dubna, Russia)

LMU – Laboratory for Muon Spin Spectroscopy

People at LMU:

Dierk Herlach (LMU Head)Bulk µSR group:

Alex Amato (Group Head), Huberturs Luetkens, Robert Scheuermann, Alexey Stoykov, Ulrich Zimmermann, Chris BainesPhD students: one open position (TU Braunschweig)

LEM group:

Elvezio Morenzoni (Group Head), Thomas Prokscha, Andreas SuterPhD students: two open positions (Univ. Zürich, TU Braunschweig)PostDocs: Dimitri Eshchenko (Univ. Zürich), Suriyakan Vongtragool (Univ. Leiden)

Technicians:

Xavier Donath (bulk, changing to SLS), Stefan Gloor (bulk+LEM), Hans-Peter Weber (LEM)Software support: Secretary:

Andrea Raselli Renate Bercher

(about 300 users from more than 20 countries per year)

Fast and Slow Muons at PSIPaul Scherrer Institut • 5232 Villigen PSI Isis Muon Training Course/...

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