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Theoretical Physics

The research in the Theoretical Physics group is primarily focused on condensed matter physics/theoretical materials science, nanoscience and electromagnetic modeling.

The group also gives a large number of courses on graduate as well as undergraduate levels.

Highlights

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Probing dopants in wide semiconductor quantum point contacts

 I.I Yakimenko and K-F Berggren.

J. Phys.: Condens. Matter, 28 (2016) 105801

Effects of randomly distributed impurities on conductance, spin polarization and electron localization in realistic gated semiconductor quantum point contacts (QPCs) have been simulated numerically. To this end  density functional theory in local spin-density approximation (LSDA) has been used. In the case when the donor layer is embedded far from the two-dimensional electron gas (2DEG) the electrostatic confinement potential exhibits the conventional parabolic form, and thus the usual ballistic transport phenomena take place both in the devices with split gates alone and with an additional metallic gate on the top. In the opposite case, i.e., when the randomly distributed donors are placed not far away from the 2DEG layer, there are drastic changes like the localization of electrons in the vicinity of confinement potential minima which give rise to fluctuations in conductance and resonances. The conductance as a function of the voltage applied to the top gate for asymmetrically charged split gates has been calculated. In this case resonances in conductance caused by randomly distributed donors are shifted and decrease in amplitude while the anomalies caused by interaction effects remain unmodified. It has been also shown that for a wide QPC the polarization can appear in the form of stripes. The importance of partial ionization of the random donors and the possibility of short range order among the ionized donors are emphasized.The motivation for this work is to critically evaluate the nature of impurities and how to guide the design of high-mobility devices.

Total electron densities in the case when a distance between two-dimensional electron gas
and donor layer is 10 nm and voltage between split gates is -1.6 V.

 


Responsible for this page: Fei Wang

Last updated: 03/07/16