Oxford Instruments is delighted to announce Dr Kate A. Ross, Assistant Professor, Dept. of Physics of Colorado State University, USA as the 2018 winner of Lee Osheroff Richardson (LOR) Science Prize for North and South America.

Brief of her publications:

1) K.A. Ross, L. Savary, B. D. Gaulin, and L. Balents. Quantum Excitations in Quantum Spin Ice. Phys. Rev. X 1, 021002 (2011). 255 citations (Google Scholar)
This paper provided quantitative exchange interactions within an anisotropic exchange model for the pyrochlore material Yb₂Ti₂O₇. These were extracted by fitting the field-polarized spin wave excitations measured my neutron scattering, at T = 50 mK and μ₀H = 5T. The extracted parameters suggested that Yb₂Ti₂O₇ is close to a new phase of matter called “quantum spin ice”, which is predicted to host “emergent electrodynamics”, i.e. quasiparticles that can be identified as spin-based magnetic monopoles, electrons, and photons. This paper spurred accelerated interest in the material and in other quantum spin ice candidates, and in general the anisotropic superexchange model that we now know accurately captures the physics of many rare earth pyrochlores. Kate took the lead on growing the single crystal for the measurement, was one of the main experimenters for the neutron beam time, performed the fits to the field polarized spin waves to extract the exchange parameters, and helped to write the paper.

2) K.A. Ross, T Proffen, H.A. Dabkowska, J.A. Quilliam, L.R. Yaraskavitch, J.B. Kycia, B.D. Gaulin. Lightly stuffed pyrochlore structure of single-crystalline Yb₂Ti₂O₇ grown by the optical floating zone technique. Phys. Rev. B 86 (17), 174424 (2012). 92 citations (Google Scholar)
This influential paper examines origin of the known sample-dependence of the magnetic properties of Yb₂Ti₂O₇, which was investigated through a careful structural study. Neutron powder diffraction results from a crushed single crystal and a pristine powder sample, which each display representative magnetic behavior of the variety of low temperature specific heat observed from Yb₂Ti₂O₇, revealed that the single crystals are “stuffed” with extra Yb on the non-magnetic Ti sublattice, while the powders are stoichiometric and thus more closely representative of the ideal behavior of Yb₂Ti₂O₇. This work led to many follow up studies from other groups, confirming and adding to this structural defect picture, and eventually helped to inspire a crystal growth method that appears to have produced unstuffed Yb₂Ti₂O₇ crystals, which should enable a clearer view of the exotic magnetic state of Yb₂Ti₂O₇. Kate led this work, producing the samples, performing the experiments, analyzing the results, and writing the manuscript.

3) K. A. Ross, Y. Qiu, J. R. D. Copley, H. A. Dabkowska, B. D. Gaulin. Order by Disorder Spin Wave Gap in the XY Pyrochlore Magnet Er₂Ti₂O₇. Phys. Rev. Lett. 112, 057201 (2014). 47 citations (Google Scholar)
This paper reports the presence of a small energy gap to the spin wave excitations in the XY antiferromagnetic pyrochlore material Er₂Ti₂O₇. This compound had been previously theorized (based on a field polarized neutron scattering study similar to that in paper 1 above) to be one of the rare material examples where “order by disorder” (i.e., fluctuations) selects the magnetically ordered ground state. However, previous studies had seemed somewhat contradictory to this, since the spin waves appeared to be gapless to within the energy resolution previously used. The measurement reported in this paper was challenging, pushing the neutron instrumentation to its resolution limit, but clearly revealed the presence of a small gap (0.02 meV). The origin of this gap has been debated since then, with competing theories about the mechanism for ground state selection – a healthy debate that has led to more interesting work on Er₂Ti₂O₇ and other XY antiferromagnetic pyrochlores. Kate performed the neutron scattering experiment, analyzed the data, and took the lead on writing the paper.