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New Magnet Displays Electronic Charge Carriers that Have Almost No Mass

Improvements in recent electronics has demanded the requisite hardware, transistors, to be smaller in each new iteration. The size of silicon transistors has been reduced to the order of 10 nm by the recent progress in nanotechnology.

However, for these small transistors, other physical effects set in, which restrict their functionality. For instance, the heat production and power consumption in these devices is developing major problems for device design. Thus, innovative quantum materials and device concepts are needed for developing a new generation of energy-saving information technology. The latest discoveries of topological materials, referring to a new type of relativistic quantum materials, prove to hold immense promise for use in energy saving electronics.

The magnetic and electronic states of newly discovered Sr1-yMn1-zSb2 are depicted by spheres representing the positions of the atoms in the crystal structure of this material with strontium (Sr) depicted by the small violet spheres; antimony (Sb) by the large blue spheres; and manganese (Mn) by the purple spheres. The arrows attached to the Mn atoms represent the magnetic moments of these atoms which align in the orientation shown to give the magnetic properties of Sr1-yMn1-zSb2. Also depicted are the energy and momentum states of the conducting electrons, or charge carriers, which have a Dirac-like dispersion relation shown in gold. Photo Credit: Oak Ridge National Laboratory

The first observation of this topological behavior in a magnet, Sr1-yMn1-zSb2 (y, z < 0.1), was recently reported by Researchers in the Louisiana Consortium for Neutron Scattering (LaCNS) headed by LSU Department of Physics & Astronomy Chair and Professor John F. DiTusa and Tulane University Professor Zhiqiang Mao. Other collaborators were from Oak Ridge National Lab, the National High Magnetic Field Laboratory, Florida State University and the University of New Orleans. These findings have been recently published in the journal Nature Materials.

This first observation is a significant milestone in the advancement of novel quantum materials and this discovery opens the opportunity to explore its consequences. The nearly massless behavior of the charge carriers offers possibilities for novel device concepts taking advantage of the extremely low power dissipation.

Professor John F. DiTusa, LSU Department of Physics & Astronomy Chair

“Topological materials” is a phrase referring to materials where the current carrying electrons behave as if they do not have mass similar to the properties of photons, the particles that are responsible for making up light. These electronic states are remarkably robust and immune to disorder and defects as they are protected from scattering by symmetry. This symmetry protection leads to extremely high charge carrier mobility, producing little to no resistance to current flow. The anticipated result refers to a considerable reduction in heat production and energy saving efficiencies in electronic devices.

This new magnet is capable of displaying electronic charge carriers that have almost no mass. The magnetism carries with it a vital symmetry breaking property, called time reversal symmetry (TRS), breaking in which the ability to run time backward would no longer return the system back to its starting conditions.

The integration of relativistic electron behavior, which is the reason for much reduced charge carrier mass, and TRS breaking has been anticipated to lead to a lot more strange behavior, referring to the much sought after magnetic Weyl semimetal phase. The material discovered via this collaboration is considered to be an exceptional one to examine for evidence of the Weyl phase and to reveal its consequences.

The Researchers involved include J.Y. Liu, J. Hu, Y.L. Zhu, G.F. Cheng, X. Liu, J. Wei, and Z.Q. Mao (Tulane University, New Orleans); Q. Zhang, W. A. Phelan, and J. F. DiTusa (Louisiana State University, Baton Rouge); D. Graf, (National High Magnetic Field Lab, Tallahassee); Q. Zhang, H.B. Cao and D. A. Tennant (Oak Ridge National Laboratory); S.M.A. Radmanesh, D.J. Adams, and L. Spinu (University of New Orleans); Marcelo Jaime and Fedor Balakirev (Condensed Matter and Magnet Science, MPA-CMMS); and I. Chiorescu (NHFML and Florida State University, Tallahassee).

The U.S. Department of Energy Office of Science, the National Science Foundation and the Louisiana Board of Regents supported this research.

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