Neutron scattering from strongly correlated electron materials: integrating theory and experiment

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Neutron scattering from strongly correlated
electron materialsintegrating theory and
experiment

• Ross McKenzie
• University of Queensland
• Workshop supported by
• and UQ

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Goals

• Help define the big questions we should try and
  answer in the next 5-10 years.
• Stimulate closer interaction of theorists with
  experimentalists.
• Define priorities for
• -new experiments
• -new calculations
• -materials synthesis

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Big questions

• Do spin liquid ground states occur in real
  materials?
• Do deconfined spinons exist in real materials?
• What is the connection between superconductivity
  and antiferromagnetic fluctuations and
  correlations?
• What is the nature and origin of the pseudogap
  phase in the cuprates?
• How do we quantify and measure fluctuations,
  especially associated with short-range order?
• What would be definitive experimental signatures
  of topological order?

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Experimental advances

• Orders of magnitude advances in
• - energy and momentum resolution
• - beam intensity statistics.
• New opportunities will result from new
  facilities coming on line in the next few years
• SNS (USA), ISIS 2nd target station (UK), and
  OPAL (Australia).
• Parameter regime of extreme conditions is
  expanding (high pressures, high magnetic fields,
  and low temperatures).
• New materials and higher-quality crystals

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Magnetic excitationsin the cuprates
Hayden, Mook, Dai, Perring, Dogan, Nature 2004
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Theoretical advances

• Calculations of the dynamical spin susceptibility
  S(q,?) for model many-body Hamiltonians.
• Calculation of excitation spectra for frustrated
  2D Heisenberg antiferromagnets
• Contributions of multi-particle excitations, by
  series expansion techniques.
• Revival of RVB theory.

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Quantitative comparison of theory and experiment
Cs2CuCl4

• Series expansion calculation of excitation
  spectra of Heisenberg model on anisotropic
  triangular lattice

Zheng, Fjaerestad, Singh, McKenzie, Coldea,
cond-mat/0506400
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Relative multi-particle contributions
Dimerised Heisenberg spin Chain. ? 0 is
decoupled dimers ? 1 is uniform chain Zheng,
Hamer, Singh, PRL (2003)
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Thanks to

• Susan Grantham
• John Fjaerestad
• Rob Robertson and ANSTO
• University of Queensland
• Australian Research Council

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