News from Nanotechjapan


Novel Bulk Rectification Effect in a Polar Semiconductor Realized by an Exotic Crystal

 On March 7, 2017, the University of Tokyo announced that a research group from the university and Riken has discovered bulk rectification effect in a layered polar semiconductor BiTeBr under the applied magnetic field. Details were published in Nature Physics with Assistant Professor Toshiya Ideue of the university as lead author *.

 Well known rectification effect is observed in translationally asymmetric interface such as semiconductor p-n junction. Although the structure of polar conductors has asymmetric nature, inherent nonreciprocal transport has not been manifested as rectification effect because of its translational symmetry. To the contrary, the research group has discovered bulk rectification effect in a polar semiconductor BiTeBr. In the crystal structure of BiTeBr, Bi, Te and Br layers are stacked along the c axis, breaking the mirror symmetry along the stacking direction. When the current I is directed perpendicular to the polar axis and the magnetic field is applied perpendicular to both I and polar axis, the electric resistance is found to be different, depending on the current direction. Experimentally observed nonreciprocal electric signals are quantitatively explained by theoretical calculations based on the Boltzmann equation considering the giant Rashba spin-orbit coupling.

* T. Ideue, K. Hamamoto, S. Koshikawa, M. Ezawa, S. Shimizu, Y. Kaneko,Y. Tokura, N. Nagaosa, and Y. Iwasa, "Bulk rectification effect in a polar semiconductor", Nature Physics (2017) doi:10.1038/nphys4056; Published online 06 March 2017