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ESRF-EBS-NRS Workshop, Grenoble, 11 - 13 March 2019 Sharpening spectral resolution and polarization purity of hard x-rays at the ESRF-EBS Ralf Rhlsberger Deutsches Elektronen-Synchrotron DESY, Hamburg Outline (1) Structure and dynamics of

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Sharpening spectral resolution and polarization purity of hard x-rays at the ESRF-EBS

Ralf Röhlsberger

Deutsches Elektronen-Synchrotron DESY, Hamburg

ESRF-EBS-NRS Workshop, Grenoble, 11 - 13 March 2019

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Page 2 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Outline

(2) Vibrational spectroscopy with µeV resolution (1) Structure and dynamics of complex materials on mesoscopic length scales (3) Enabling technology: High purity polarimetry (5) Outlook: High-energy polarimetry (4) Applications of high purity polarimetry

  • Revealing anisotropies in condensed matter
  • Spinwave spectroscopy
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Page 3 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

A ´simple´ system (atom, molecule) Composites Self-Organization A ´complex´ system Emergence

Pico- seconds Micro- seconds Milli- seconds

Length Time

Mesocosmos

0.1 nm 1 nm 10 nm 100 nm 1 µm 10 µm Nano- seconds Femto- seconds

eV meV µeV neV peV Energy

The quest for x-rays with ultrasmall emittance: Understanding dynamics

  • n mesoscopic length

scales

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Page 4 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Vibrational dynamics on mesoscopic length scales (1 nm – 100 nm)

Artificially structured materials

Photonic and phononic crystals

Nanocomposites

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Page 5 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Dynamics of artificially structured materials

Phononic crystal Dynamical properties are modified due periodic variation

  • f elastic properties

This allows to tailor the vibrational properties of new materials by adjusting their structure Vibrational excitations play an important role for energy dissipation upon friction à Nanocomposites (e.g. metal/polymer, amorphous/crystalline)

  • T. Gorishnyy et al., Phys. Rev. Lett. 94, 115501 (2005)

Energy (µeV) 5 10

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Page 6 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

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Page 7 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Anisotropy à optical activity

Collaboration with I. Uschmann,

  • G. Paulus et al., FSU + HI Jena

Crossed polarizers for hard X-rays

Enabling Technology: High-purity Polarimetry

Polarization Purity

  • Efficient selection of s à p scattering
  • Detection of very weak anisotropies

(linear, circular)

  • B. Marx et al.,
  • Opt. Commun. (2011)
  • Phys. Rev. Lett. (2013)
  • H. Bernhardt et al.,
  • Appl. Phys. Lett (2016)

4-bounce polarizer for 14.4 keV (B. Marx et al.)

δ = #$/#& = 10)*+ … 10)-

Si

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Page 8 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

fn(ω) fn(ω)

Magnetic hyperfine interaction Electric hyperfine interaction Optical activity in (nuclear ) resonant scattering

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Page 9 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Rotating mirror, coated with 57Fe, for Doppler shifting

polarizer analyzer

Si(840)

Spectrometer principle

f = 20000 rpm

2 cm

20 µm Energy scan by transverse displacement of disk sample

Polarizer Analyzer

High-resolution inelastic scattering with µeV-resolution 10 µm 57Fe APD array

Scanning range Energy band width Photon flux

∆E = ± 1 meV δE = 2 µeV F ~ 107 ph/s

Spectrometer throughput and spectral resolution are determined by the source parameters !

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Page 10 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

ESRF-EBS Source Parameters

4 m undulator (18 mm period, k = 2)

à Improvements at ID18 mostly due to the small horizontal source size

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Page 11 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Small source size + collimation à small horizontal beam cross section and small divergence

  • A. Q. R. Baron et al., Appl. Phys. Lett. 74, 1492 (1999)

Refractive collimator

CRL plane wave point source

Collimation down to 1 µrad seems feasible at the ESRF-EBS Values < 1 µrad in combination with asymmetric Bragg reflections

Polarimetry at ultralow-emittance storage rings

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Page 12 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

The quest for ultrahigh purities: Polarization of the Vacuum à vacuum becomes birefringent

Photon-photon scattering

„ … even in situations where the photon energy is not sufficient for matter production, its virtual possibility will result in a polarization of vacuum and hence in an alteration of Maxwells equations“

  • Z. Physik 98, 714 (1936)
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Page 13 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

  • T. Heinzl, R. Sauerbrey et al., Opt. Commun. 267, 318 (2006)

Detection of Vacuum Birefringence: Probing the quantum vacuum

a fine structure constant z0 interaction length l probe wavelength I0 electric laser field IC critical field for pair production = 4.4 x 1029 W/cm2

for I0 = 1022 W/cm2 and l = 1 Å à ellipticity < 10-12 expected Δφ = 4α 15 z0 λ I0 IC

Ellipticity

à Purities d ~ 10-12 required

high-power laser polarizer analyzer x-ray beam

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Page 14 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

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Page 15 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Fundamental limitations of the polarization purity (a) Multiple wave diffraction (b) Beam divergence

For a Gaussian beam with H/V divergencies sH and sV:

d ~ 10-12 for sV , sH ~ 1 µrad

s à p polarization transfer limits the purity for multiple reflections

Polarization purity

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Page 16 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Charge anisotropy in a iron spin crossover (SCO) compound

SCO complex with a strong EFG at the position of the Fe atom

[Fe(PM-BiA)2(NCS)2]

Molecular packing, monoclinic phase High-spin Low-spin T > 170 K

Collaboration with L. Scherthan, J. Wolny, V. Schünemann (TU Kaiserslautern)

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Page 17 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Change of EFG orientation upon spin-crossover results of DFT calculations high-spin low-spin

[Fe(PM-BiA)2(NCS)2]

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Page 18 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Nuclear resonance polarimetry of an SCO complex

  • 135 -120 -105
  • 90
  • 75
  • 60
  • 45
  • 30
  • 15

50 100 150 200 250 counts c (°)

experimental data simulation

Rotation angle c I = Iπσ (t)∝(sin χ ⋅cos χ)2

c T = 220 K, high-spin

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Page 19 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

20 40 60 80 100

  • 100
  • 80
  • 60
  • 40

cMIN (°)

j (°)

c-Scan theory

50 100 150 200 250 50 100 150 25 50 75 25 50 75 25 50 75

  • 160
  • 140
  • 120
  • 100
  • 80
  • 60
  • 40
  • 20

25 50 75

j =45° j =65°

counts

j =80° j =90° j =0° j =-90°

c (°)

Rotation angle j

T = 220 K, high-spin

Nuclear resonance polarimetry of an SCO complex

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Page 20 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Results: Electric field gradient in the high-spin state DFT calculations Measured data

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à Change of EFG orientation due to the SCO

  • 160
  • 140
  • 120
  • 100
  • 80
  • 60
  • 40
  • 20

1 10 100 1000

Impulse c (°)

T=120 K Raumtemperatur

j =80°

counts

T=120 K Room temperature

Experimental results: Temperature dependence

Diploma thesis Lena Scherthan, Uni Kaiserslautern (2016)

T = 120 K T = 120 K T = 220 K Significant contribution from high-spin phase Evaluation reveals: 78 % low-spin, 22 % high-spin (oriented !)

Nuclear resonance polarimetry of an SCO complex

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Page 22 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Analyzer plane

a

d

B, dE/dz

k0

(a)

Polarizer plane Sample

Static Anisotropies

à Polarization rotation

W

k0

(b)

L

B

Dynamic Anisotropies

à Polarization precession

Probing Anisotropies in Condensed Matter via Polarimetry

Probing charge anisotropies in correlated materials à Adressing selected orbitals via resonant x-rays Probing spin excitations in magnetic materials à PRL 112, 117205 (2014)

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Page 23 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Linear Doppler effect: à scattering of light from a moving object with broken translational invariance

ΔE = Δ ! k ⋅ ! v Δ ! k = 2 ! k0  v  k0

Energy Transfer in Inelastic Light Scattering

à solid-state excitation: Phonon (corresponds to a moving mirror) à solid-state excitation: Magnon (corresponds to a rotating phase retarder)

− ! k0

A half-wave plate acts an angular mirror à

ΔL = 2!

Angular Doppler effect: à scattering of light from a rotating object with broken rotational invariance (optical anisotropy)

ΔE = Δ ! L⋅ ! Ω

W

! m

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Page 24 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Rotational anisotropy in solids is generated by magnetization Dynamic anisotropy in spin waves:

Magnons (Spinwaves)

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Page 25 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Transformation into linear basis:

Resonant Scattering from Magnons: Twisted Polarization

S = πc Ω

Sample with magnon excitation

AS ⎡ ⎣ ⎤ ⎦lin = cos2Ωt AH −sin2Ωt A

V

Polarization precession in space

AS ⎡ ⎣ ⎤ ⎦circ = iei 2ΩtA

− +e−i2ΩtA +

Transmission through a rotating half-wave plate / Light scattering from a magnon

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Page 26 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

Position-sensitive detector

Sample

Analyzer in crossed setting .

from polarizer

I(q,t) Resonant Scattering from Magnons: Polarization Analysis

I(q,t) = IB+ I0 S(q,Ω) cos2Ωt

−∞ ∞

∫

dΩ

Measured signal: Intermediate scattering function

  • Compare with Neutron

Spin Echo

  • Energy transfer encoded

in polarization

  • Independent of energy

bandwidth ! Accessible range of spinwave frequencies: 1 – 500 GHz à Probing low-energy magnetic excitations

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Page 27 | Sharpening energy resolution and polarization purity | Ralf Röhlsberger, ESRF-EBS-NRS Workshop, 11 - 13 March 2019

6 T magnetic field in Faraday geometry

Outlook: A synchrotron Mössbauer source for 40K

Transition energy: 29.8 keV Lifetime: 8 ns Natural abundance: 0.01 % Relevant for:

  • biological functions
  • unconventional

superconductors Requires extension of polarimetry to high energies !

Energy (G0) KCl crystal, 0.5 mm thick s à p scattering BMBF Verbund projekt FSU Jena

Potential reflections: B