Hall effect

The Search for Quantum Anomalous Hall Insulators

David Vanderbilt
Monday, October 16, 2017 - 4:30pm to 5:30pm

The quantum Hall effect, discovered 35 years ago, is a bizarre phenomenon in which a 2D gapped system can nevertheless carry a current.  Moreover, the transverse conductivity of the system is precisely quantized in units of e^2/h.  Unfortunately, this behavior requires a strong perpendicular magnetic field, and has only been observed at low temperatures.  Work of Haldane in 1988 raised the possibility that similar physics could be observed in two-dimensional magnetic systems without any external magnetic field, and potentially at much higher temperatures.  Such a system is known as a "...

Large Anomalous Hall Effect in a Half-Heusler Antiferromagnet

  • By Aude Marjolin
  • 20 July 2016

Recently a team of researchers from MIT, the NIST Center for Neutron Research (NCNR), Carnegie Mellon University, and the Beijing Institute of Technology have experimentally demonstrated a "hybrid material" solution to this problem. They studied a compound of three elements, gadolinium, platinum and bismuth, known together as a ternary compound. In their compound, gadolinium supplies the magnetic order while the platinum-bismuth components support a topological electronic structure. These two components acting in concert make a correlated material that is more than the sum of its parts, showing quantum mechanical corrections to electrical properties at an unprecedented scale. Their results were reported July 18 in Nature Physics.

The theoretical aspect of the collaborative effort was with professors Di Xiao of Carnegie Mellon University and Wanxiang Feng of Beijing Institute of Technology, who provided first principles electronic structure calculations based on the experimental data taken at MIT, NCNR, and the NHMFL to determine the underlying electronic character of this new materials system.