The Neutron Resonance Spin Echo Option @ V2/FLEXX at BER...

Klaus HabichtHelmholtz-Zentrum Berlinfür Materialien und Energie

The Neutron Resonance Spin Echo Option @ V2/FLEXX at BER II

Klaus Habicht, Master Class on Neutron Precession Techniques, Erice, 4th July 2017 2

Key Question

Is an NRSE option better than a dedicated instrument?

V2/FLEXX, the cold-neutron host spectrometer

Features of the NRSE option at V2/FLEXX


Acknowledgements

FLEX-upgrade project

Duc Manh Le – now STFC, ISIS, UKMarkos Skoulatos – now MLZ, Germany Kirrily Rule – now ANSTO, Australia

Diana Lucía Quintero-Castro, now Univ. Stavanger, Norway

Rasmus Toft-Petersen, now DTU, Denmark

Zhilun Lu, HZB, GermanyZita Hüsges, HZB, GermanySiqin Meng, HZB, Germany

Thomas Krist, HZB, Germany

NRSE

Felix Groitl – now at EPFL and PSI,Thomas Keller, MPI Stuttgart, Germany


Probing Material Structures: Scattering Techniques

structure dynamics

Neutron scattering techniques probe static or dynamic correlations

Inte

nsity

(arb

itrar

y un

its)

Distance of lattice planes d (Å)

Ener

gy tr

ansf

er (m

eV)

Wavevector q [h h 0] (r.l.u.)

Klaus Habicht, Master Class on Neutron Precession Techniques, Erice, 4th July 2017

2.0 2.5 3.00.0

0.5

1.0

1.5 data model

5

Probing Material Structures: Scattering Techniques

structure dynamics

Neutron scattering techniques probe static or dynamic correlations

Inte

nsity

(arb

itrar

y un

its)

Distance of lattice planes d (Å)1 2 3 4 5

0.0

0.5

1.0

1.5

2.0

Wavevector [h h 0] (r.l.u.)

Ene

rgy

trans

fer (

meV

)


1 2 3 4 50.0

0.5

1.0

1.5

2.0


Ene

rgy

trans

fer (

meV

)

1 2 3 4 50.0

0.5

1.0

1.5

2.0


Ene

rgy

trans

fer (

meV

)

6

Dispersion relates quasiparticle energy to quasiparticle momentumEnergy width in the dispersion encodes quasiparticle lifetime

NRSE Motivation: Quasiparticle Linewidth

∆𝐸𝐸


2 3 4 50.0

0.2

0.4

0.6

0.8

1.0

Sca

tterin

g S

igna

l (a.

u.)

Energy transfer (meV)2 3 4 5

0.0

0.2

0.4

0.6

0.8

1.0

Sca

tterin

g si

gnal

(a.u

.)

Energy transfer (meV)

7

Energy linewidth 𝛤𝛤 inversely proportional to lifetime 𝑇𝑇𝐷𝐷 : 𝛤𝛤 = ℏ/𝑇𝑇𝐷𝐷

Quasiparticle Linewidth and Lifetime

0 10 200.0

0.2

0.4

0.6

0.8

1.0

Sca

tterin

g si

gnal

(a.u

.)

Correlation time τNSE (ps)

energy domain time domain

𝑒𝑒−𝜏𝜏𝑁𝑁𝑁𝑁𝑁𝑁𝑇𝑇𝐷𝐷 = 𝑒𝑒−

Γ𝜏𝜏𝑁𝑁𝑁𝑁𝑁𝑁ℏ

energy domain

∆𝐸𝐸exp2Γ

0 10 200.0

0.2

0.4

0.6

0.8

1.0

Scat

terin

g si

gnal

(a.u

.)

Correlation time τNSE (ps)


The Upgraded Cold Neutron TAS FLEXX

Velocity selector

Polarizer Optional collimators

Ellipticalguide

Virtualsource

Doublefocusing

monochromator

PG and Heusleranalyzer

3He detector

new primary spectrometer optimized for high flux and low background and optional

polarized neutron capabilities

gain factor 2-10 for flux at sampleM. D. Le, et al., Nucl. Inst. Meth. A 729, 220-226 (2013)


FLEXX standard TAS mode

Neutron Resonance Spin Echo Option

MultiFLEXX backend

FLEXX Options

XYZ polarization analysis


FLEXX Polarizer: S-Bender

beam cross section: 60 mm x 125 mm

400 wafers 0.15 x 125 x 120 mm3

Fe-Si multilayer with m = 3

anti-reflecting Gd-layer/Si/Gd-layer

magnetization field > 300 G


FLEXX S-Bender Transmission

device transmission FLEXX transmission as measured with monitor at sample position

-2 -1.5 -1 -0.5 0 0.5 1 1.5 20

0.1

0.2

0.3

0.4

0.5

0.6

0.7

rocking angle [deg]

spin

up

trans

mis

sion

[%]

-30 -10 10 300

0.1

0.2

0.3

0.4

0.5

0.6

0.7

horizontal translation [mm]

spin

up

trans

mis

sion

[%]

1.1 1.3 1.5 1.7 1.9 2.1 2.3 2.5 2.70

0.1

0.2

0.3

0.4

0.5

kI [Å-1]

spin

up

trans

mis

sion

[%]

polarizer transmission is confirmed at FLEXXtransmission is entirely due to device transmission

assuming meff=3


FLEXX S-Bender Transmission

polarizer rocking scans kI=2.56 Å-1

(measurements by Mirrotron) polarizer rocking scan at FLEXX kI=2.66 Å-1

as measured with monitor at sample position

angular acceptance of polarizer is confirmed at FLEXX

-2 -1.5 -1 -0.5 0 0.5 1 1.5 20

0.1

0.2

0.3

0.4

0.5

0.6

rocking angle [deg]

spin

up

trans

mis

sion

[%]

FLEXXMirrotron x=10 mmMirrotron x=20 mmMirrotron x=30 mm


FLEXX Primary Spectrometer Guide Field

13M. Skoulatos, K. Habicht, NIM A 647 100 (2011)

Guide Field Calculations 1/4

• Calculations using Radia code from ESRF in Mathematica

• Magnetic field from Radia used to calculate beam depolarization using a depolarization formalism by Rosman and Rekveldt [1]

• McStas simulations

14

Guide Field Design Checks

Guide

CollimatorMonochromator

Shielding

[1] Rosman and Rekveldt, Z. Phys. B – Cond.Mat. 79, 61-68 (1990) Duc M. Le

Guide Field Calculations 1/4

• Calculations using Radia code from ESRF in Mathematica

• Magnetic field from Radia used to calculate beam depolarization using a depolarization formalism by Rosman and Rekveldt [1]

• McStas simulations

15

Guide Field Design Checks

[1] Rosman and Rekveldt, Z. Phys. B – Cond.Mat. 79, 61-68 (1990) Duc M. Le


FLEXX Guide Field Realization


FLEXX Monochromator Helmholtz Coils


FLEXX Polarisation

experimental polarization • decreases towards larger wavelengths as expected from MC simulation• does depend on virtual source width and monochromator curvature

1 1.25 1.5 1.75 2 2.25 2.50

10

20

30

40

50

60

kI (Å-1)

Flip

ping

Rat

io

1 1.25 1.5 1.75 2 2.25 2.50.8

0.85

0.9

0.95

1

kI (Å-1)

Pol

ariz

atio

n

Experiment: 2mm Virtual SourceExperiment: 20mm Virtual SourceMC Simulation: 5 x 5 x 5 mm3


FLEXX Heusler Analyzer Performance

3 rows, 15 crystals each Cu2MnAl (111) Bragg peak0.42° mosaic (individual crystals) fixed vertical, variable horizontal curvaturevertical 0.17 T magnetization field beam cross section: 60 mm x 125 mm

horizontal focussing gain ~2.5-3


NRSE Option at V2/FLEXX


New bootstrap coils for the NRSE option at FLEX(in collaboration with MPI Stuttgart / FRM II)

• increase in accepted beam width

• access to steeper dispersion by larger coil tilt angles

• access to larger scattering angles for Larmor diffraction

• improved magnetic shielding in the NRSE arms

21

courtesy: Max Planck-Institut

für Festkörperphysik Stuttgart

F. Groitl et al., Rev. Sci. Instrum. 86, 025110 (2015)

Upgrade of NRSE Option at V2/FLEXX


New bootstrap coils for the NRSE option at FLEX(in collaboration with MPI Stuttgart / FRM II)

• increase in accepted beam width

• access to steeper dispersion by larger coil tilt angles

• access to larger scattering angles for Larmor diffraction

• improved magnetic shielding in the NRSE arms

22

courtesy: Max Planck-Institut

für Festkörperphysik Stuttgart


Upgrade of NRSE Option at V2/FLEXX


NRSE Coupling Coils



NRSE Option at V2/FLEXX

24



Direct Beam Calibration Measurements

50 100 150 200 250 300 3500.0

0.2

0.4

0.6

0.8

1.0

P0 correction 4 PIP0 correction 8 PI

P0

tau [ps]

kI=kf=1.40 Å-1

kI=kf=1.57 Å-1


NRSE Science at V2/FLEXX and TRISP !

thermal transport in thermoelectric SrTiO3

Goal: benchmark first-principles DFT / MD simulations with interatomic force constants

including anharmonic lattice dynamics

SrTiO3 phonon dispersion calculated mode Grüneisen parameters

needs experimental access to phonon lifetimes at low spin echo times

L. Feng, T. Shiga, J. Shiomi, Appl. Phys. Express 8, 071501 (2015)


Thermoelectric SrTiO3

SrTiO3 phonon dispersion experimental line broadening

0.00 0.02 0.04 0.06 0.08 0.10 0.120

500

1000

1500

2000300 K Γ-R direction

Gaussian FWHM FLEXX ΓHWHM TRISP NRSE

Line

bro

aden

ing

[µeV

]

ζ [r.l.u.]

0.0 0.1 0.2 0.3 0.4 0.50

2

4

6

8

10

12

14

16

18

20

(0.5 0.5 0.5)(0 0 0)

ener

gy [m

eV]

ζ [r.l.u.]

TA data Stirling Born von Karman model FLEXX TAS

Γ-R direction


“Instrumental” Resolution for NRSE

• use Gaussian approximation of TAS transmission probability TTAS(ki,kf)• expand total Larmor phase φ(ki,kf) to second order• expand energy conservation to second order• integrate by matrix technique

at very large spin echo timesinstrumental resolution has to be

considered

..),(),(1 33),( cckdkdeTSN

P fii

fiTASfi +∆= ∫ kkkkQ φωbeam divergence

0 1 2 3 4 50.1

1 SM -1 SS +1 SA +1 [2 -0.1 0] SM -1 SS +1 SA -1 [2 -0.1 0] SM -1 SS -1 SA -1 [2 +0.1 0] SM -1 SS -1 SA +1 [2 +0.1 0]

Pola

rizat

ion

τ [ns]

instrumental limit

upper limit typical phononmeasurements


0 10 20 30 40 50 60

0.1

1

τNSE [ps]

Pola

rizat

ion

29

Development of Resolution Theory

Development of analytical resolution function for NRSE spectroscopyData correction: no convolution divide data by calculated resolution function

K. Habicht et al., Physica B 350 E803-E806 (2004)K. Habicht et al., J. Appl. Cryst. 36, 1307 (2003)

resolution function (mosaic + curvature)

curvature of the dispersion surface

Ε

q

reciprocal lattice vector G

∆η

Δ𝐸𝐸

Ε

q

Δ𝐸𝐸

sample mosaic

raw data


Neutron Spin-Echo: Semi-Classical Model

Dispersive excitations require tilted magnetic field regions

vphononv1

v2

The Neutron Resonance Spin Echo Option @ V2/FLEXX at BER...

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