The Research On The Transport Properties Of Electrons In Graphene Under External Fields

Since graphene was prepared in2004, it has attracted extensively attention due toits stable, flexible, solid properties as well as good conductivity. Especially, theunique electron transport properties, including Klein tunneling, Zitterbewegung,unconventional half-integer quantum Hall effect, etc., have become hot topics inphysics. However, because of the gapless electronic band structure, the perfecttransmission at the normal incidence makes graphene difficult to be used in themanufacture of tunneling quantum devices. Therefore, the researches on quantumtunneling and electron transport properties which are associated with the generationand the modulation of the energy gap are of vital significance. In this Dissertation,two aspects are addressed based on the modulation of the energy gap of graphene byexternal fields. One is the tunneling time and the Hartman effect in the graphenebarrier in the presence of the strain and magnetic field. The other is the coherentmanipulation of electrons transport in graphene by external fields in analogy to thephenomena in quantum optics, which can be used to suppress the current oscillation.The main results obtained are as follows.Firstly, we study the tunneling time and the Hartman effect in graphene barrier inthe presence of the strain field. We find the group delay can be enhanced bytransmission resonance in the propagating case, while the Hartman effect will happenin the evanescent case. The relationship between the dwell time and the group delay isderived in the presence of the strain field, to clarify the essence of the Hartman effect.Secondly, we study the electron transport in the presence of the magnetic field. Itis shown that the magnetic field has significant effects on transmission and groupdelay, which results in the modulation of group delay, the Hartman effect as well asthe relationship between the group delay and dwell time. Furthermore, thecontribution of Goos-H nchen shift to the delay time and the Hartman effect areanalyzed in two-dimensional problem.Finally, we have explored the coherent control of the state populations for electron and holes by the external electric fields. Transitionless quantum driving andinvariant-based inverse engineering are applied to realize the suppression ofLandau-Zener transition, which could prevent population inversion and suppress thecurrent oscillation.