Study of a stroboscopic model of a quantum dot

UBL - phd migration 201

Weak localization of the open kicked rotator

We present a numerical calculation of the weak localization peak in the magnetoconductance for a stroboscopic model of a chaotic quantum dot. The magnitude of the peak is close to the universal prediction of random-matrix theory. The width depends on the classical dynamics, but this dependence can be accounted for by a single parameter: the level curvature around zero magnetic field of the closed system.Comment: 8 pages, 8 eps figure

Exponential sensitivity to dephasing of electrical conduction through a quantum dot

According to random-matrix theory, interference effects in the conductance of a ballistic chaotic quantum dot should vanish $\propto(\tau_{\phi}/\tau_{D})^{p}$ when the dephasing time $\tau_{\phi}$ becomes small compared to the mean dwell time $\tau_{D}$. Aleiner and Larkin have predicted that the power law crosses over to an exponential suppression $\propto\exp(-\tau_{E}/\tau_{\phi})$ when $\tau_{\phi}$ drops below the Ehrenfest time $\tau_{E}$. We report the first observation of this crossover in a computer simulation of universal conductance fluctuations. Their theory also predicts an exponential suppression $\propto\exp(-\tau_{E}/\tau_{D})$ in the absence of dephasing -- which is not observed. We show that the effective random-matrix theory proposed previously for quantum dots without dephasing explains both observations.Comment: 4 pages, 4 figure

Weak localization of the open kicked rotator

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Momentum noise in a quantum point contact

Ballistic electrons flowing through a constriction can transfer momentum to the lattice and excite a vibration of a free-standing conductor. We show (both numerically and analytically) that the electromechanical noise power P does not vanish on the plateaus of quantized conductance -- in contrast to the current noise. The dependence of $P$ on the constriction width can be oscillatory or stepwise, depending on the geometry. The stepwise increase amounts to an approximate quantization of momentum noise.Comment: 4 pages including 4 figure

Exponential sensitivity to dephasing of electrical conduction through a quantum dot

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Quantum-to-classical crossover of mesoscopic conductance fluctuations

We calculate the system-size-over-wave-length ($M$) dependence of sample-to-sample conductance fluctuations, using the open kicked rotator to model chaotic scattering in a ballistic quantum dot coupled by two $N$-mode point contacts to electron reservoirs. Both a fully quantum mechanical and a semiclassical calculation are presented, and found to be in good agreement. The mean squared conductance fluctuations reach the universal quantum limit of random-matrix-theory for small systems. For large systems they increase $\propto M^2$ at fixed mean dwell time $\tau_D \propto M/N$. The universal quantum fluctuations dominate over the nonuniversal classical fluctuations if $N < \sqrt{M}$. When expressed as a ratio of time scales, the quantum-to-classical crossover is governed by the ratio of Ehrenfest time and ergodic time.Comment: 5 pages, 5 figures: one figure added, references update

Dynamical model for the quantum-to-classical crossover of shot noise.

We use the open kicked rotator to model the chaotic scattering in a ballistic quantum dot coupled by two point contacts to electron reservoirs. By calculating the system-size-over-wave-length dependence of the shot-noise power we study the crossover from wave to particle dynamics. Both a fully quantum-mechanical and a semiclassical calculation are presented. We find numerically in both approaches that the noise power is reduced exponentially with the ratio of Ehrenfest time and dwell time, in agreement with analytical predictions

MM20 HVMOS Model : a surface-potential-based LDMOS model for circuit simulation (Chapter 3)

MOS Model 20 is an advanced public-domain compact LDMOS model, to be used for circuit simulation of high-voltage IC-designs. By combining the description of the MOSFET channel region with that for the drift region of an LDMOS device, MOS Model 20 includes all specific high-voltage aspects into one model. This chapter presents the physical background of the model, the model parameter extraction strategy, and ends with the verification in comparison to dc- and ac-measurements