Skip to main content

Colloquium: Benjamin G. Ueland (Ames Lab & ISU)

Oct 20, 2022 - 4:10 PM
to , -

Speaker: Benjamin G. Ueland (Ames National Laboratory & Iowa State University)

Title: Exploring Itineracy, Frustration, and Topology in Magnetic 122-Pnictides

Abstract: Understanding the details behind magnetic correlations in quantum materials is key to discovering new functionalities and platforms for future technologies. In this talk, I will discuss some of our group’s latest work understanding magnetic frustration and itineracy in Ca(Co1 xFex)2 yAs2 [1] and the antiferromagnetic ordering of the topological quantum material EuIn2As2 [2]. For Ca(Co1 xFex)2 yAs2, our neutron scattering data show that hole doping suppresses both the static and dynamic components of the magnetic moment while maintaining a high degree of magnetic frustration. We find that this is due to tuning towards a Stoner-type transition, with hole doping moving the Fermi level away from a peak in the electronic density of states associated with a flat conduction band. For EuIn2As2, analysis of our neutron diffraction data finds novel low-symmetry helical antiferromagnetic order which can support an axion insulator phase. We further find that certain crystal surfaces are expected to host an exotic gapless Dirac cone which is unpinned to specific crystal momenta whereas other surfaces have gapped Dirac cones and exhibit half-integer quantum-anomalous-Hall type conductivity. A modest applied magnetic field of μ0H ≈ 1 T can tune between the gapless and gapped surface states.
This research was supported by the U.S. Department of Energy, Office of Basic Energy Sciences, Division of Materials Sciences and Engineering under Contract No. DE-AC02-07CH11358. Part of this research was supported by the Center for Advancement of Topological Semimetals, an Energy Frontier Research Center funded by the U.S. Department of Energy Office of Science, Office of Basic Energy Sciences, through the Ames Laboratory.
[1] B. G. Ueland, S. Pakhira, B. Li, A. Sapkota, N. S. Sangeetha, T. G. Perring, Y. Lee, L. Ke, D. C. Johnston, and R. J. McQueeney, “Carrier tuning of Stoner ferromagnetism in ThCr2Si2-structure cobalt arsenides”, Phys. Rev. B 104, L220410 (2021).
[2] S. X. M. Riberolles, T. V. Trevisan, B. Kuthanazhi, T. Heitmann, F. Ye, D. C. Johnston, S. L. Bud’ko, D. Ryan, P. C. Canfield, A. Kreyssig, A. Vishwanath, R. J. McQueeney, L.-L.Wang, P. P. Orth, and B. G. Ueland, “Magnetic crystalline-symmetry-protected axion electrodynamics and field-tunable unpinned Dirac cones in EuIn2As2”, Nat. Commun. 12, 1 (2021).

Short Bio: Ben Ueland earned his BA and MS in Physics from Binghamton University in 2000 and 2001, and his PhD in Physics from the Pennsylvania State University in 2007. His thesis work used low temperature ac magnetic susceptibility, magnetization, and heat capacity measurements to study cooperative magnetic relaxation in geometrically frustrated rare-earth pyrochlores. After graduation, Ben joined the NIST Center for Neutron Research as a National Research Council Postdoctoral Associate to learn neutron scattering techniques. In 2010, he joined the Condensed Matter Magnet Science Group at Los Alamos National Laboratory as a G. T. Seaborg Institute Postdoctoral Fellow and studied the effects of magnetic frustration in itinerant rare-earth and actinide magnets. In December 2012, Ben came to Ames as a Postdoctoral Associate working with Prof. Alan Goldman, Dr. Andreas Kreyssig, and Prof. Robert McQueeney.  Since 2016, he has been a staff scientist at Ames National Laboratory specializing in neutron and x-ray scattering measurements of magnetic correlations in quantum materials. From 2019 to 2021 he served in the Chair line of the American Physical Society’s Forum for Early Career Scientists.