New magnet discovered: Controlling dirac fermions with zero mass

Hideaki Sakai (Associate Professor) at Osaka University and Shintaro Ishiwata (Associate Professor), Hidetoshi MASUDA (Graduate Student) at The University of Tokyo succeeded in the synthesis of high-quality single crystals of EuMnBi₂, a layered compound which is thought to have both properties of Dirac fermions and magnets, using flux growth in a high vacuum. This material features hybrid architecture consisting of two-dimensional layers of bismuth 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 30-60 tesla) at The Institute for Solid State Physics of The University of Tokyo and the High Field Laboratory for Superconducting Materials of Tohoku University.

Furthermore, in order to elucidate the magnetic state, this group conducted magnetic scattering experiments using synchrotron 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 depending on the magnetic order of europium. It was also found that when a magnetic field was applied perpendicularly to the two-dimensional Bi layers and the direction of magnetic moment was rotated by 90 degrees, the conductivity perpendicular to the layers was suppressed by 1000 percent and Dirac fermions were confined within each layer.

By confining Dirac electrons in the two-dimensional layer of Bi through the use of this effect, this joint group observed 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.