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Branton Campbell in the lab

Branton J. Campbell

Professor

Department of Physics & Astronomy

Brigham Young University

Provo, UT 84602, USA

Tel: 801-422-5758, Fax: 801-422-0553

Email: branton_campbell[at]byu.edu

//physics.byu.edu/faculty/campbell/

Research Interests

I apply state-of-the-art x-ray and neutron scattering techniques to study local and long-range structures in a variety of complex solids, including fast-ion conductors, ferroelectric relaxors, high-temperature superconductors, and colossal magnetoresistive manganites, where nanoscale structural features influence macroscopic physical properties. This includes the development of symmetry-mode analysis as a tool for the determination, refinement and interpretation of distorted structures involving lattice strains, atomic displacements, magnetic moments and occupational orderings at both commensurate and incommensurate wavevectors.

Selected Publications

NMR study of ammonium magnesium langbeinite

BYU Authors: Branton J. Campbell, Harold T. Stokes, and Juliana Boerio-Goates, published in Phys. Rev. B

Recent studies have shown that ammonium langbeinites have low-temperature phase transitions uncharacteristic of the rest of the langbeinite family. In this study, proton NMR spin-lattice relaxation times T1 and spin-spin relaxation times T2 for powder samples of (NH4)2Mg2(SO4)3 are reported in the temperature range from 77 to 373 K. The ammonium ions occupy two different kinds of sites in the crystal. The measured barrier to thermally activated ammonium reorientations is found to be 2.0 and 3.3 kcal/mol for the two sites, respectively. Additionally, there is no observable discontinuity in T1 at the reported phase transition at 161 K, in agreement with heat-capacity studies, suggesting that the transition mechanism may be different from those of most langbeinites.

Goldhelox: A Soft X-Ray Solar Telescope

BYU Authors: D. S. Durfee, J. W. Moody, K. D. Brady, C. Brown, B. Campbell, M. K. Durfee, D. Early, E. Hansen, D. W. Madsen, D. B. Morey, P. W. A. Roming, M. B. Savage, P. F. Eastman, and V. Jensen, published in J. X-ray Sci. Technol.

The Goldhelox Project is the construction and use of a near-normal incidence soft x-ray robotic solar telescope by undergraduate students at Brigham Young University. Once it is completed and tested, it will be deployed from a Get-Away-Special (GAS) canister in the bay of a space shuttle. It will image the sun at a wavelength of 171-181Å with a time resolution of 1 sec and a spatial resolution of 2.5 arcsec. The observational bandpass was chosen to image x-rays from highly ionized coronal Fe lines. The data will be an aid in better understanding the beginning phases of solar flares and how flaring relates to the physics of the corona-chromosphere transition region. Goldhelox is tentatively scheduled to fly on a space shuttle sometime in 1995 or 1996. This paper outlines the project goals, basic instrument design, and the unique aspects of making this an undergraduate endeavor.

Enumeration and tabulation of magnetic (3+d)-dimensional superspace groups

BYU Authors: Harold T. Stokes and Branton J. Campbell, published in Acta Crystallogr. Sect. A

A magnetic superspace group (MSSG) simultaneously constrains both the magnetic and non-magnetic (e.g. displacive, occupational, rotation and strain) degrees of freedom of an incommensurately modulated magnetic crystal. We present the first enumeration and tabulation of all non-equivalent (3+d)-dimensional magnetic superspace groups for d = 1, 2 and 3 independent incommensurate modulations, along with a number, symbol and reference setting for each group. We explain the process for generating an exhaustive set of inequivalent magnetic superspace groups, describe several examples, and show how the tables can be accessed via the ISO(3+d)D interface within the ISOTROPY Software Suite. We recommend that published incommensurate magnetic structures indicate a magnetic superspace-group number and symbol from these tables, as well as the transformation matrix from the published group setting to the reference setting used in these tables.

Introducing a unified magnetic space-group symbol

BYU Authors: Branton J. Campbell and Harold T. Stokes, published in Acta Crystallogr. Sect. A

The two commonly used systems of magnetic space-group (MSG) symbols, with accompanying numbers and settings, are those of Belov–Neronova–Smirnova (BNS) and Opechowski–Guccione (OG). The symbols from both systems have been used for several decades now. Both have advantages and disadvantages. Both present challenges of interpretation to novice and expert users alike, which can inhibit understanding and lead to errors in published magnetic structures. To address each of these challenges going forward, a new unified (UNI) MSG symbol is introduced, which combines a modified BNS symbol with essential information from the OG symbol.

Theoretical and computational improvements to the algebraic method for discovering cooperative rigid-unit modes

BYU Authors: Branton J. Campbell, Harold T. Stokes, Tyler B. Averett, Shae Machlus, and Christopher J. Yost, published in J. Appl. Crystallogr.

A linear-algebraic algorithm for identifying rigid-unit modes in networks of interconnected rigid units has recently been demonstrated. This article presents a series of enhancements to the original algorithm, which greatly improve its conceptual simplicity, numerical robustness, computational efficiency and interpretability. The improvements include the efficient isolation of constraints, the observation of variable-block separability, the use of singular value decomposition and a quantitative measure of solution inexactness.