Electronic Structure And Local Transport Properties In 2DEG

Transport properties in mesoscopic systems are one of the hot topics in condensed matter physics and materials science.The phase coherence of charge carriers gives rise to many novel transport properties in mesoscopic systems.2DEG is the ideal system to study these new physical phenomena,especially under a magnetic field.However,most of pervious works focused mainly on the total conductance of the systems.But how does a current flow through a mesoscopic system? The answer to this question is not only of the necessary for better understanding the quantum phenomena but also of the great importance for developing the future nanodevice.Nowadays,one can study the local current in a mesoscopic system experimentally by scanned probe microscopes in low temperature.However,in a range of tens of nanometers,this question has only been addressed in theoretical.In this work,we study the local transport properties of 2DEG by the recursive green ' s function method.The thesis consists of five chapters.In chapter one,we introduce the mesoscopic systems and two dimensional electron gas including typical structure,characteristics,development history and application prospect.And then,the quantum point contact(QPC)is included.The second chapter introduces the model and computational method.The tight-binding model and Green's function formalism are presented in details.The three chapter,based on the tight-binding method,we investigated the energy spectrum and localization of electronic states in 2DEG subjected to a spatially local gradient magnetic field.Considering the numerical accuracy,the actual calculated of magnetic field was used in this work.By adjusting the width of stripe d and the amplitude of magnetic field in one magnetic strip model,the energy spectra and the square root of probability density were obtained and we found some interesting phenomena.We also studied the case of four stripes on the top of 2DEG.For emphasizing the effect of magnetic field,the harmonic potential was removed.The four chapter,we calculated the conductance and local current density with Green's function formalism,and exhibited images of current distribution vividly.We can find the phenomenon of quantization in conductance and different pattern of current in the results.And then,we designed two quantum dot contact models with different method,etching method and saddle potential.We found oscillations from conductance quantized steps because of abrupt contraction region.The oscillations were connected with ratio of the channel.Finally,The conductance quantized steps was changed with different width of quantum dot contact,and the reason was energylevel changed.In addition,we also observed the current beam being reflected and coherent transporting in image of current.The last chapter presents a conclusion of this work and some prospects for this investigation.