Materials Science Research Lecture
Webinar Link:
https://caltech.zoom.us/j/95708772987
Webinar ID: 957 0877 2987
Abstract:
Lamellar insulating materials with magnetic ions on the kagome lattice of corner-sharing triangles have attracted much attention over the years because of the geometrical frustration and the consequent lack of magnetic ordering at low temperatures.
Now it turns out that the non-collinear antiferromagnetic ordering induced by the longer range and inter-kagome-layer interactions of a semi-metal can have interesting effects on quantum transport. Specifically, the AB stacked kagome layers of Mn3X form an anti-chiral co-planar magnetic order that gives rise to strong anomalous Hall and Nernst effects at room temperature linked to Weyl points in the electronic band structure[1].
I shall describe an experimental study of the magnetic order and excitations in Mn3Ge[2]. While a phenomenological spin Hamiltonian including exchange interactions, Dzyaloshinskii-Moriya interactions, and single-ion crystal field terms can describe aspects of the Mn-based magnetism, spin-wave damping, and the extended range of magnetic interactions indicate the strong interactions with conduction electrons that underly its quantum transport anomalies.
The talk will illustrate the constructive interplay between the pursuit of a fundamental understanding of electrons in solids and the discovery of materials with novel properties for technological applications.
* This work was supported as part of the IQM Energy Frontier Research Center funded by the U.S. Department of Energy under Award No. DE-SC0019331 and by the Gordon and Betty Moore Foundation under GBMF4532.
[1] "Large anomalous Hall effect in a non-collinear antiferromagnet at room temperature," S. Nakatsuji, N. Kiyohara and T. Higo, Nature 527 (2016) 212-215.
[2] "Antichiral spin order its Goldstone modes and their hybridization with phonons in the topological semimetal Mn3Ge," Y. Chen, J. Gaudet, S. Dasgupta, G. G. Marcus, J. Lin, T. Chen, T. Tomita, M. Ikhlas, Y. Zhao, W. C. Chen, M. B. Stone, O. Tchernyshyov, S. Nakatsuji, C. Broholm, Phys. Rev. B 102, 054403, (2020).
More about the speaker:
COLLIN LESLIE BROHOLM is the Gerhard H. Dieke Professor in the Department of Physics and Astronomy at the Johns Hopkins University. He earned his Ph.D. from the University of Copenhagen in 1988, was a post doc at AT&T Bell Laboratories from 1988-1990 and joined Johns Hopkins in 1990.
An experimental condensed matter physicist, Dr. Broholm is interested in anomalous forms of magnetism, superconductivity, and their interplay. Of particular interest are crystalline materials where quantum effects are enhanced on account of competing interactions (frustration) or low dimensionality.
The main experimental tool is neutron scattering and Dr. Broholm has a long-standing involvement in development of the corresponding instrumentation. He has built two spectrometers at the NIST Center for Neutron Research and has served on various committees overseeing instrumentation development at National facilities for Neutron Scattering.
Dr. Broholm received the Presidential Faculty Fellowship in 1994, became a fellow of the American Physical Society in 2004, and received the Sustained Research Award of the Neutron Scattering Society of America in 2010. He was selected for funding by the Gordon and Betty Moore foundation as one of 19 top experimentalists in the area of quantum materials in 2014. Dr. Broholm is the director of the Johns Hopkins Institute for Quantum Matter (https://iqm.jhu.edu).