Bandstructure calculations for holes in GaAs and simulations of dc conductance in electron quantum point contacts

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Copyright: Fricke, Sebastian
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Abstract
We present simulations of the bandstructure of holes in GaAs for an infinite square well potential using the Luttinger Hamiltonian and subband k•p theory. Our calculations explicitly include Rashba and Dresselhaus spin-orbit terms. The effective mass of the holes at the zone center is calculated. The calculations show that the Rashba and Dresselhaus terms change the hole bandstructure and should not be ignored. We looked at the accuracy of different methods of obtaining the Landè g-factor g* from QPC conductance measurements. We simulated data for a parabolic QPC saddle-point potential at T=0 K and analyse the data using methods based on the AC conductance and on the DC conductance. We show that the two methods are compatible and accurate to ±4 % for the ideal simulated data set, which is free of experimental artefacts. We investigated how much accuracy is lost if the two methods are used on real experimental data. Therefore we analysed conductance data from QPC measurements where the 2DEG density in the reservoirs adjacent to the QPC can be changed independently from the applied QPC gate voltage. We were able to investigate the dependence of g* on the density. We conclude that the method based on the DC conductance should not be used to determine g* from QPC conductance measurements. We present simulations of the 0.7 feature known from QPC measurements. We were looking at three scenarios in which a spontaneous spin gap opens and is responsible for the occurrence of the 0.7 feature. The spin gap depends linearly on the gate voltage. The scenarios differ in the point at which the spin gap opens. We looked at different opening rates, closing spin gaps, applied magnetic fields and source-drain bias. We compared the AC transconductance plots derived from simulated data to experimental data to get clues about how the spin gap opens and closes. We found that a gap with a finite size at the opening point best resembles experimental data.
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Author(s)
Fricke, Sebastian
Supervisor(s)
Micolich, Adam P.
Hamilton, Alexander R.
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Publication Year
2014
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Thesis
Degree Type
Masters Thesis
UNSW Faculty
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