David E. Moncton: Research

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Research Publications Summary

Charge Density Waves

Neutron Scattering Study of the Charge-Density Wave Transitions in 2H-TaSe2 and 2H-NbSe2, D. E. Moncton, J. D. Axe, F. J. DiSalvo, Phys. Rev. B 16, 801 (1977).

Broken Hexagonal Symmetry in the Incommensurate Charge-Density Wave Structure of 2H-TaSe2, R. M. Fleming, D. E. Moncton, D. B. McWhan, F. J. DiSalvo, Phys. Rev. Lett. 45, 576 (1980).

These papers represent a body work comprising 13 papers over 10 years using both neutron and x-ray scattering studies to reveal and elucidate the remarkable physics of incommensurate charge density wave systems predominantly in the layered transition metal dichalcoginides. The discovery of incommensurate phases, transitions to commensurate phases, studies of the relevant phonon dynamics and the discovery of the spontaneous formation of stripe phases in CDW materials were among the pioneering discoveries.

Magnetism and Superconductivity

Neutron Scattering Study of Magnetic Ordering in the Reentrant Superconductor ErRh4B4, D. E. Moncton, D. B. McWhan, J. Eckert, G. Shirane, W. Thomlinson, Phys. Rev. Lett. 39, 1164 (1977).

Coexistence of Antiferromagnetism and Superconductivity: A Neutron Diffraction Study of DyMo6S8, D. E. Moncton, G. Shirane, W. Thomlinson, M. Ishikawa, Ø. Fischer, Phys. Rev. Lett. 41, 1133 (1978).

These papers represent a body of work comprising 7 papers over 5 years which demonstrated the interactions between superconducting and magnetic order parameters within the same materials for the first time. For superconductors containing a regular lattice of magnetic ions it was shown that nominally ferromagnetic interactions can be suppressed and driven to finite wavevector, while for antiferromagnetic interactions it was shown conclusively that ordered antiferromagnetism can co-exist with superconductivity and does so in a number of materials.

Two-Dimensional Phase Transitions

Synchrotron X-ray Study of the Commensurate-Incommensurate Transition of Monolayer Krypton on Graphite, D. E. Moncton, P. W. Stephens, R. J. Birgeneau, P. M. Horn, G. S. Brown, Phys. Rev. Lett. 46, 1533 (1981).

Melting of Variable-Thickness Liquid-Crystal Thin Films: A Synchrotron X-ray Study, D. E. Moncton, R. Pindak, S. C. Davey, G. S. Brown, Phys. Rev. Lett. 49, 1865 (1982).

Pioneering efforts to develop high resolution x-ray scattering techniques for the first time at the Stanford synchrotron were applied to two different two-dimensional (2D) model systems: rare gases adsorbed on a single crystal graphite surface, and freely suspended (substrate free) liquid crystal films. This body of work consists of 23 papers over 10 years where the basic nature of long range order in 2D phase transitions was elucidated. Discoveries included rotational and translational incommensurability transitions, and liquid to solid transitions involving the first observation of the intermediate hexatic phase, where lattice orientational order is established without long range translational order.

High-Temperature Superconductors

Antiferromagnetism in La2 CuO4-y, D. Vaknin, S. K. Sinha, D. E. Moncton, D. C. Johnston, J. M. Newsam, C. R. Safinya, H. E. King, Jr., Phys. Rev. Lett. 58, 2802 (1987).

Shortly after the discovery of high-temperature superconductivity in 1986, this neutron scattering study demonstrated that the undoped parent compound was an ordered spin ½ antiferromagnet. With nearly 1000 citations this paper and three others laid out the details which were crucial to understanding the fundamental role of magnetic interactions in these remarkable materials.

Rare Earth Magnetism

Magnetic X-ray Scattering with Synchrotron Radiation, D. E. Moncton, D. Gibbs, J. Bohr, Nucl. Instr. and Meth. A 246, 839 (1986).

Magnetic X-ray Scattering Studies of Holmium Using Synchrotron Radiation, D. Gibbs, D. E. Moncton, K. L. D'Amico, J. Bohr, B. H. Grier, Phys. Rev. Lett. 55, 234 (1985).

A new method for using synchrotron radiation for high-resolution scattering with x-ray polarization analysis allowed x-ray studies (5 papers) to make major new discoveries in rare earth magnetism, including the discovery of the important role of spin discommensurations, or spin slips, in understanding unique wave vector lock-in transitions undetected in decades of previous neutron scattering studies.

Advanced Photon Source

Physics Research Opportunities with Synchrotron X-Radiation, D. E. Moncton, Major Materials Facilities Committee of the National Academy of Sciences (Washington, D.C., 1984).

The Advanced Photon Source: Performance and Results from Early Operation, D. E. Moncton, J. Synch. Rad. 5, 152 (1998).

The first paper above was the presentation of the scientific case for building the Advanced Photon Source to a committee of the National Academy of Sciences. This Committee ranked APS the highest priority for new synchrotron facilities, and this recommendation was largely responsible for urging DOE to construct the facility. The second paper describes the performance achieved by the facility 14 years later.

Neutron Focusing Optics

Demonstration of a novel focusing small-angle neutron scattering instrument equipped with axisymmetric mirror, D. Liu, B. Khaykovich, M. V. Gubarev, J. L. Robertson, L. Crow, B. D. Ramsey, and D. E. Moncton, Nature Communications, 2013.

Demonstration of Achromatic Cold-neutron Microscope Utilizing Axisymmetric Focusing Mirrors., D. Liu, M. V. Gubarev, B. D. Ramsey, D. Hussey, D. Jacobson, M. Arif, D. E. Moncton, and B. Khaykovich, Applied Physics Letters 102, 183508 (2013); doi: 10.1063/1.4804178.

Recent research in collaboration with NASA has led to the first available aberration-free optics for neutron scattering and imaging instruments. The first paper describes an experiment in collaboration with Oak Ridge National Laboratory in which a demonstration small-angle neutron scattering (SANS) set-up achieved a performance level that would extrapolate to a 50-fold improvement for an optimized instrument. The second paper described an experiment at NIST demonstrating similar large potential performance enhancements for neutron imaging. Subsequently NIST has funded the construction of such an instrument at NRC. These optics have effectively moved the field of neutron scattering from the era of ‘pin-hole cameras’ into a modern era based on focusing optics.

Compact High-Brilliance X-ray Sources

MIT inverse Compton source concept, W. S. Graves, W. Brown, F. X. Kaertner, D. E. Moncton, Nucl. Instr. and Meth. A 608, S103–S105 (2009).

Intense Superradiant X Rays from a Compact Source Using a Nanocathode Array and Emittance Exchange, W. S. Graves, F. X. Kaertner, D. E. Moncton, and P. Piot, Phys. Rev. Lett. 108, 263904 (2012).

In this work significant progress has been made to utilize advances in accelerator and laser technology to develop new concepts for compact laboratory-scale x-ray sources that have characteristics similar to, or potentially better than, synchrotron radiation. In the first paper, a laser field replaces the standard undulator magnet allowing the electron beam energy to be lowered to the range of 20 MeV, and therefore machine size and cost can be dramatically reduced. The x-ray performance is similar to a second generation synchrotron facility such as NSLS I. In the second paper novel methods for creating a modulated electron beam are explored, so that coherent x-ray emission would result, thus providing a significant performance enhancement similar to an x-ray free-electron laser. These new x-ray source concepts will permit x-rays to be utilized in many dedicated applications not possible with large billion-dollar facilities. One such application is for semiconductor metrology, which is now being studied together with NIST researchers.