Landolt-Börnstein - Group III Condensed Matter

4 Frequency- and time-dependent effects


This chapter discusses frequency- and time-dependent effects in quantum point contacts (QPCs). The dynamical properties of quantum point contact systems have motivated a significant number of theoretical and experimental investigations not least because of potential device applications. In the following, the appropriate theory and the accompanying experimental evidence are presented. Using a finite difference method the time evolution of a Gaussian wavepacket prepared at the entrance to a QPC can be followed. A detailed analysis of photon-assisted tunneling in QPCs based upon an adiabatic treatment of the slowly varying confinement potential arising from the gate-electrodes has shown that the problem can be treated regardless of the polarization of the high-frequency field. The broadband investigation of the far infrared photoresponse of ballistic QPCs was designed to investigate photon-assisted transport in such devices. The photoconductance in a QPC device exposed to high-frequency radiation is illustrated. The interaction between a ballistic QPC and a surface acoustic wave (SAW) modifies the current-voltage characteristics. The influence of SAW upon the conductance of ballistic channels is of particular interest due to its potential application as a current standard and experimental investigations of such properties were performed. The absence of photon-assisted tunneling has been attributed to the exponential dependence of the photon-excited transition probability upon the localization of the high-frequency field. Another early experimental observation of the noise in QPCs attributed the observed suppression to a modulation of the scattering resulting from a single impurity within the constriction of the QPC.

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4 Frequency- and time-dependent effects
Book Title
Electronic Transport. Part 1: Quantum Point Contacts and Quantum Wires
II Quantum point contacts
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Landolt-Börnstein - Group III Condensed Matter
  • B. Kramer
  • Authors
  • D. Wharam
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