Magnetic Switching And Spin Filter Based On The Two-Dimensional Topological Insulators

As a kind of new material, topological insulators(TIs) have caught the attention of most scientific research workers since their discovery and the research for them has become the focus in the modern condensed matter in recent years, due to their singularity characteristics different from the traditional insulators and metals. As same as the common insulators, it is a insulating state with energy gaps in their bulk, but for the strong spin-orbit interaction, it is a metal state with no energy gaps in their edges or surfaces. This kind of metal state is determined by the topological structure of the bulk electron states and protected by the time-reversal symmetry, thus TIs are robust against non magnetic impurities and disorders and carries in their surfaces can transport without loss. For these new physical properties, TIs possess very high value of scientific research in the fields of quantum computation and spintronics. Therefore, it is very significant to research how to control the electrons in the edge states.As a building block of electronic devices, the magnetic double-barrier structure has been studied in various systems such as conventional semiconductor two-dimensional electron gas, graphene, and helical metals. In this article, we study the electron transport properties of a HgTe quantum spin Hall system modulated by a planar magnetic double-barrier. Using the Kwant software based on the python language, we calculate the probability density distribution of the incident electrons and how the conductance changes with the Fermi energy and the magnitude of the nonuniform magnetic field. It indicates that for an electron incident from a quantum-spin-Hall state in leads, the transmission can depend strongly on the relative orientation of the two magnetic barriers as its energy is near the bulk conduction band of leads. When the magnetization of the two magnetic barriers is the same, the electron can transmit nearly perfectly for a proper spin orientation. If the magnetization is opposite, the transmission is spin-independent and can be suppressed drastically. These indicate:(1) When the magnetization of the magnetic double barriers is anti-parallel, it can be used as a switch to control the switch-on and switch-off state of the edge channel in HgTe.(2) When the magnetization of the magnetic double barriers is parallel, it can be used as a spin filter so the electron with a proper spin orientation can transmit through the device.