Discovery of a magnet capable of controlling Dirac fermions with zero mass
A group of researchers from Osaka University and The University of Tokyo succeeded in synthesizing two-dimensional layers of bismuth (Bi) with Dirac electrons and magnetic multilayer blocks of europium.
Using flux growth in a high vacuum, this group succeeded in the synthesis of EuMnBi2, a layered substance of high-quality single crystal thought to have both properties of Dirac fermions and magnets. This substance features hybrid architecture consisting of two-dimensional layers of Bi with Dirac electrons and europium with magnetic properties.
In order to verify the strong correlation between Dirac fermions and the magnetic state, this group measured electric resistance in a strong magnetic field (some 30 to 60 tesla) at The Institute for Solid State Physics of The University of Tokyo and the High Field Laboratory for Superconducting Materials of Tohoku University.
In order to elucidate the magnetic state, the group conducted magnetic scattering experiments of radiated x-rays at the Photon Factory of the Institute of Materials Structure Science, High Energy Accelerator Research Organization.
As a result, they found that electric resistance significantly changed according to the magnetic order of europium. They also found that when a magnetic field was applied perpendicularly to the surface and the direction of magnetic moment was rotated by 90 degrees, the conductivity perpendicular to the surface was suppressed by 10 percent and Dirac fermions were confined within the surface.
Furthermore, by confining Dirac electrons in the two-dimensional layer of Bi, or the superconducting layer, through the use of this effect, this joint group achieved a bulk half-integer quantum Hall effect, in which the value of the Hall resistance becomes discrete, in a bulk magnet of Dirac fermions for the first time.
This group's achievement will develop a new field of study, strong correlated quantum conductance of Dirac electrons, and contribute to realizing super high-speed spintronics, the foundation of high-speed and energy-saving electronics.
More information: H. Masuda et al. Quantum Hall effect in a bulk antiferromagnet EuMnBi2 with magnetically confined two-dimensional Dirac fermions, Science Advances (2016). DOI: 10.1126/sciadv.1501117
Journal information: Science Advances
Provided by Osaka University