Past and Future Insights from Neutron Scattering Collin Broholm * Johns Hopkins University and NIST Center for Neutron Research  Virtues and Limitations of Neutron Scattering  New Sources and Instrumentation  Capabilities of New Instrumentation  Conclusions * supported by NSF DMR

Fisk Fest 8/15/01 Zachary Fisk and Neutron Scattering  More than 70 papers on neutron scattering:  Heavy Fermion Systems  Kondo Insulators  Valence Fluctuating systems  High T C superconductors  Neutrons used to probe  Magnetic order and Fluctuations  Structure and sample quality  Thermal Expansion  Phonons

Fisk Fest 8/15/01 Spin Fluctuations in U 2 Zn 17 Broholm et al. PRL (1987)

Fisk Fest 8/15/01 Structure of YbInCu 4 d-spacing (A) Intensity (10 3 counts/  s) Lawrence et al PRB (1996) Contrast between elements with similar Z Sensitivity to light atoms in heavy matrix Contrast between elements with similar Z Sensitivity to light atoms in heavy matrix a probe of sample quality Flux-grown crystal

Fisk Fest 8/15/01 Magnetic Structure of CeRhIn 5 Bao et al PRB (2000)

Fisk Fest 8/15/01 Probing Spin Density Distribution UPt 3 U 5f, 6d, and -7f spin polarization Pt polarized as well U 5f, 6d, and -7f spin polarization Pt polarized as well UBe 13 Only U polarized Neumann, Brown, et al. Physica B (1991)

Fisk Fest 8/15/01 Electronic Interactions in La 2 CuO 4 Coldea et al PRL (2001)

Fisk Fest 8/15/01 What makes it hard  150 MeV thermal energy per neutron (fission)  a factor Z 2 less than X-ray scattering  Limitations of current instrumentation  dynamics in samples < 1 mm 3  dynamics in nano-structured solids  Lateral surface structure  complex materials with weak signals  Signals from impurities at low concentration  Spatial and temporal resolution  Pressure above 25 GPa

Fisk Fest 8/15/01 Expanding Applicability of a Powerful Probe  Increase source brightness  Increase spectral brightness by cooling neutrons  Increase temporal brightness in pulsed neutron source  Improve beam delivery system  Match solid angle to wave vector resolution requirements  Match bandwidth to energy resolution requirements  Increase solid angle of detection system  Position sensitive detectors  Crystal analyzer arrays

Fisk Fest 8/15/01 New Instrumentation and Sources  NIST cold source and instrument upgrade  HFIR cold source and instrument upgrade 2002  LANSCE source and instrument upgrade 2002  US Spallation Neutron Source 2006  German high flux research reactor 2004  Australian high flux research reactor 2005  Japanese Spallation Neutron Source 2006  European Spallation Neutron Source ?  Chinese Advanced Research reactor ?

InstrumentBegin  E (meV) Condensed Matter Science Enabled FANS Phonon Density of States Spin Echo Flux lattice dynamics Dynamic Correlations in Glasses Back Scattering Critical Phenomena Quantum Tunelling Disc Chopper Quantum Critical phenomena Phonon density of states MACS Structure of fluctuating systems Impurity dynamics Inelastic Scattering from small samples New Instruments for CMP at NIST

Fisk Fest 8/15/01 Intensity from Focusing 1428 cm 2 PG(002) MC Simulation Qiu and Broholm (2001) MACS monochromator

Fisk Fest 8/15/01 Upgraded Neutron Scattering Facilities at HFIR, ORNL

Upgraded Neutron Scattering Facilities at LANSCE

Fisk Fest 8/15/01

May 2001 Aug

Instruments for CMP at SNS

Fisk Fest 8/15/01 Neutrons in the 21 century  Chemical and magnetic structure at the interfaces of nano- scale artificially structured systems  Excitations in materials patterned on the nano-scale  Protein structure (including D-positions) and dynamics  Complete 4 D Q-E mapping of dynamic correlation function for spin and lattice in large single crystals 0<E<100 meV  Systematic access to order parameters of weak or complex broken symmetry phases  Inelastic neutron scattering as a super-susceptometer for screening new materials  Parametric and complete information about structure of matter under extreme conditions

Fisk Fest 8/15/01 Conclusions  Neutrons are great but we don’t have enough yet  New sources and instrumentation should produce a renaissance for the technique  New facilities must be easily accessible to non- neutron-experts to broaden the science program