Inelastic Neutron Scattering B. Fultz, J. Lin, O. Delaire, M. Kresch Caltech

1. Inelastic Neutron ScatteringB. Fultz, J. Lin, O. Delaire, M. Kresch Caltech Science interestsWhere is the field going?Tasks and goals of the DANSE subprojectLooking for new scientific opportunities

2. Excitations in Solids: An Optical Illusion of Space-Time Correlations

6. ARCS software is going well

7. ARCS reduction software demo…

8. WBS 10: Science Scope for Inelastic Scattering 1) spin correlations in magnets, superconductors, and materials close to metal-insulator transitions 2) vibrational excitations in solids and their relationship to phase diagrams and equations of state of materials 3) tunneling and reorientation transitions of small molecules on surfaces 4) vibrational spectra of molecules or individual atoms such as hydrogen 5) diffusional motions and relaxation processes studied by quasielastic scattering

9. Tasks for Inelastic Scattering WBS 10 10.1.1.1 Data reduction for CNCS 08/31/06 02/15/07 10.1.1.2 Data reduction for SEQUOIA 03/01/08 08/16/08 10.1.2.1 Data reduction for HYSPEC 05/06/10 07/06/10 10.1.2.2 Data reduction for Backscatter 02/07/07 03/16/07 10.2.1.1 Gilat-Raubenheimer method 01/05/08 03/08/08 10.2.1.2 Pack and Monkhorst method 03/11/10 05/08/10 10.2.2.1 Polycrystal 07/31/07 01/06/08 10.2.2.2 Single Crystal 11/13/08 06/14/09 10.2.2.3 Dispersion Algorithms 08/12/08 11/14/08 10.2.3 Separation of Nuclear and Spin Scattering 11/23/09 03/16/10 10.2.4.1 CLIMAX 04/21/07 08/11/07 10.2.5 Chemical Spectroscopy Preprocessing 03/01/10 02/28/11 10.3.1.1 Coherent Inelastic Scattering Kernel 03/11/07 04/21/07 10.3.1.2 Incoherent Inelastic Scattering Kernel 04/06/07 04/21/07 10.3.1.3 G(r,t) from individual neutron scatterings 03/25/08 11/09/08 10.3.1.4 G(r,t) from dynamics simulation 07/03/10 09/18/10 10.3.2.1 Multiple scattering correction 04/21/09 12/06/09 10.3.3 Disordered Spin Dynamics 04/13/09 02/28/11

10. Science Activity for Physical Chemistry: Dynamics of Excited Materials and Molecules • Density-functional methods have revolutionized the calculation of electronic structure • They are not justified for excited states, however. • New effort to study excited states of molecules by pump-probe Raman spectrometry

11. Science Activity for Physical Chemistry: Hydrogen Molecule Dynamics in Physisorption Rotational Librational Ground Excited

12. Entropy W is the number of equivalent ways of finding a system with the same macrostate. Ways of “what”?

13. Classical Limit p1…p3N–3 ( ) V1 DS = kB ln V2 1 2 q1…q3N–3 ~1/w

14. Phonon DOS of V with 3d-series solutes • increasing stiffening along 3d series • Ti: softening, • Cr-Ni: stiffening • impurity masses ~ host • trend opposite to mass increase • electronic / size effect

15. Entropy of Alloying

16. Use Case Inelastic Scattering with Fermi Chopper Instruments • Goal: Obtain phonon partition function, Z(T). • Approach: - Reduce NeXus file to “S(Q,E)” - S(Q,E) to phonon DOS, g(E) -

17. Today – Three Problems • s/M differs between atoms (neutron weighting) • Q information will be rich, but neglected in analysis • Errors in Z are unknown - reliability of thermodynamic quantities? Computation will Solve These

18. Today (Neutron De-weighting Solution)

19. Near Future: Fits with Q information

20. New Capability

21. Error Bars in Thermodynamic Quantities

22. Error Bars in Thermodynamic Quantities

23. Test Case – Use Known Force Constants from Ni

24. Resolution of a Fermi Chopper Spectrometer (e.g., Windsor) ~4.2 for ARCS

25. ARCS Has Moveable Fermi Choppers

26. Typical ARCS Resolution (Energy Dependent)

27. Multiple Energies Give Higher Resolution

28. Summary of WBS 10: Inelastic Scattering Scope for: - physical chemistry of small molecules - phonon excitations in solids - magnetic excitations in solids Progress with ARCS and other inelastic instruments has been crucial for establishing the science scope Experience in materials theory is essential too

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