Electrostatic control of quantum Hall ferromagnetic transition, a step   toward reconfigurable network of helical channels
  Ferromagnetic transitions between quantum Hall states with different polarization at a fixed filling factor can be studied by varying the ratio of cyclotron and Zeeman energies in tilted magnetic field experiments. However, an ability to locally control such transitions at a fixed magnetic field would open a range of attractive applications, e.g. formation of a reconfigurable network of one-dimensional helical domain walls in a two-dimensional plane. Coupled to a superconductor, such domain walls can support non-Abelian excitation. In this article we report development of heterostructures where quantum Hall ferromagnetic (QHFm) transition can be controlled locally by electrostatic gating. A high mobility two-dimensional electron gas is formed in CdTe quantum wells with engineered placement of paramagnetic Mn impurities. Gate-induced electrostatic field shifts electron wavefunction in the growth direction and changes overlap between electrons in the quantum well and d-shell electrons on Mn, thus controlling the s-d exchange interaction and the field of the QHFm transition. The demonstrated shift of the QHFm transition at a filling factor $\nu=2$ is large enough to allow full control of spin polarization at a fixed magnetic field. 
Aleksandr Kazakov, George Simion, Yuli Lyanda-Geller, Valery   Kolkovsky, Zbigniew Adamus, Grzegorz Karczewski, Tomasz Wojto...
cond-mat.mes-hall