Probing magnons with Xrays

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Probing magnons with X-rays

• Luuk Ament
• In collaboration with Fiona Forte Jeroen van
  den Brink

Lorentz-Institute, Leiden University
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Indirect RIXS
Synchrotron radiation
Interestingsample
4p
wres (5-10 keV)
1s
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Why RIXS?

• Second order process
• Momentum dependence
• Supplementary to neutron scattering

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La2CuO4

• Perovskite layers of CuO2

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La2CuO4

• Perovskite layers of CuO2

• Cu 3d eg holes behave as Heisenberg spins
• Ground state is antiferromagnetically ordered

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La2CuO4

• Perovskite layers of CuO2

• Cu 3d eg holes behave as Heisenberg spins
• Ground state is antiferromagnetically ordered
• Collective excitations magnons

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What happens in RIXS?

• Actually, the Heisenberg model can be derived
  from a Hubbard model in the limit U gtgt t with J
  2t2/U
• The 1s core-hole creates a potential which
  effectively changes U, and therefore J.

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What happens in RIXS?

• Actually, the Heisenberg model can be derived
  from a Hubbard model in the limit U gtgt t with J
  2t2/U
• The 1s core-hole creates a potential which
  effectively changes U, and therefore J.

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Calculation

• Kramers-Heisenberg relation gives the cross
  section

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Calculation

• Kramers-Heisenberg relation gives the cross
  section
• Approximate ? gtgt En

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Calculation

• Kramers-Heisenberg relation gives the cross
  section
• Approximate ? gtgt En
• Hamiltonians conserve Sz only 2-magnon processes!

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Results

• Good agreement with recent experiments by John
  Hill et al. at Argonne
• Vanishing intensity at q (0,0) and q (?,?)
• Peak in intensity at q (?,0) and ? 500 meV

Theory Theory experimental resolution