Electric/Magnetic Manipulated Transport Properties Of The Surface/Edge State Dirac Electron In Strong Topological Insulators

Topological insulators are a novel state of quantum matter with an insulating bulkgap and topologically protected gapless Dirac-type edge or surface states on the boundary,due to its peculiar band structures. Topological insulators have been involved in manyimportant physical phenomena and physical mechanisms, has broad application prospects,therefore, it rapidly become one of the hottest topics in condensed matter physics andsemiconductor devices fields. In this master’s degree paper, after a systematic introductionof the basic theory of topological insulators, we focus mainly on the electric and magneticmanipulation of the electronic transport properties for surface/edge state Dirac electronin topological insulators, which include the following three topics:(1)We theoretically investigate the electrically controllable spin polarization, selec-tivity efciency, and tunnelling magnetic resistance of the edge state Dirac electron ina two-dimensional topological insulator quantum well sandwiched between ferromagneticelectrodes by using the method of the Keldysh non-equilibrium Green’s function. A nearlyfull spin polarization of the topological edge state with giant inversion is observed,～80%;the selectivity efciency for the edge state Dirac has been demonstrated to be larger than90%for the first time; the system tunnelling magnetic resistance from the spin-valve efectis observed to be up to65000%; as can be efectively modulated by the spin-conservingand spin-flipping tunneling coupling of the edge states.(2)Transport properties on the surface of topological insulator Bi2Se3under themodulation of a two-dimensional ferromagnet/ferromagnet junction are investigated us-ing the wave function matching approach. Adjusting the direction and the strength ofthe magnetic proximity exchange will tune the single ferromagnetic barrier into totaltransmission and the transmission blockade status. The transmission probability for thedouble ferromagnetic insulators modulated n n junction first increases rapidly and thendecreases slowly with the increase of the magnetic proximity exchange strength, whilefollowing with a contrary variation of the band gaps, that of n p junction demonstratesan opposite trend. Moreover, the transmission probability presents a π periodic changewith respect to the barrier strength Z, varying proximity exchange shifts the amplitudeof transmission probability but does not change its frequency. (3)Based on the theorem of semiconductor inter-subband transition, the optical ab-sorption properties of the electrons in the vicinity of Dirac point on the surface of topolog-ical insulator Bi2Se3have been investigated. It has been demonstrated that, the opticalabsorption properties under the modulation of circularly polarized light are demonstratedto be diferent with diferent structural parameters. The single-photon absorption spectrashowed three absorption peaks at some determine frequency, the second and third peakshould shift to higher frequency with the increase of electric field, while the first peak isalmost unchanged. The double-photon absorption spectra showing a bimodal structure,however, the absorption peak in the higher frequency range would be vanished with theincrease of the inversion symmetry breaking.