Conductance of a quantum point contact in the presence of a scanning probe microscope tip

Abstract

Using the recursive Green's function technique, we study the coherent electron conductance of a quantum point contact in the presence of a scanning probe microscope tip. Images of the coherent fringe inside a quantum point contact for different widths are obtained. It is found that the conductance of a specific channel is reduced while other channels are not affected as long as the tip is located at the positions correspending to that channel. Moreover, the coherent fringe is smoothed out by increasing the temperature or the voltage across the device. Our results are consistent with the experiments reported by Topinka et al. (Science 289, 2323(Science 289, (2000).PACS numbers: 73.23.-b, 73.43.Cd, 73.20.At (Phys. Rev. B 65, 205321 (2002)) Quantum point contacts (QPCs) formed in twodimensional electron gases (2DEGs) have attracted significant attention for the past two decades. 1,2 Since the discovery of the conductance quantization in these structures, 1 QPCs have been widely used in a variety of investigations, including transport through quantum dots, the quantum Hall effect, magnetic focusing, and the Aharonov-Bohm effect. 2

Chemical and magnetic impurity effects on electronic properties of semiconductor quantum wires

“…Therefore the atomic lines will have different contributions in carrier transport and cause the quantum interferences, which can be important in the process of charge transport through nano- scale devices. Similar feature in the coherent electron conductance of a quantum point contact in the presence of a scanning probe microscope tip, has been reported both experimentally 27 and theoretically 28 . Now, we discuss the band-edge energy shift and the band broadening due to the random distribution of M ions and the fluctuation of localized spins.…”

Green’s function technique for studying electron flow in two-dimensional mesoscopic samples

“…The standard recursive Green's function method used in Ref. 9 to obtain the same result is not very efficient because one has to start over the complete conductance calculation for every position of the tip. The numerical effort then scales like M 4 N 2 in the number of operations, where M is the width and N is the length of the system (N ≫ 1), and one therefore is limited to small systems.…”

Local and general aspects of current profiles in quantum magnetotransport

“…This behavior is a further manifestation of chirality in broken time-reversal symmetry, and is investigated below with numerical simulations. Notice that in the presence of time reversal, obstacles modify in general both the local current and the net transport current, as pictured for instance by the scanning probe microscope techniques [1] and theoretical imaging of currents [11].…”