|M.Sc Student||Zamir Aviad|
|Subject||Effect of Contact Magnetoresistance on Thermodynamic|
Magnetization Measurements of a Two Dimensional
|Department||Department of Physics||Supervisor||Professor Michael Reznikov|
|Full Thesis text|
The work is devoted to the thermodynamic measurement of the spin magnetization of a two dimensional electron gas.
A two dimensional electron gas (2DEG), a many-body system in nature, has long been a subject of intensive theoretical and experimental investigation. Despite this effort, at low electron densities, when electron-electron interactions play an important role, many fundamental questions remain open. The examples are the nature of the metal to insulator transition observed with decreasing the electron density of the system, and the effect of in-plane magnetic field on this transition, and on transport properties of the 2DEG in general.
Understanding the magnetization of a 2DEG at low densities would provide better knowledge on the nature of electron-electron interactions and might be helpful in testing different theoretical approaches used to tackle the problem.
The original objective of this research was the investigation of the temperature dependence of the 2DEG spin susceptibility. Most of the theoretical works predict a linear in temperature correction to the spin susceptibility, however they differ not only in their value, but even in sign. We report measurements of the spin magnetization of a 2DEG, realized on a Si-SiO2 interface, in the temperature range from 1.8 K to 4.2 K and in magnetic field from 0.4 to 1 T. The thermodynamic method we used measures the charge induced at the gate of a structure by a change of the chemical potential of the electron layer. The chemical potential changes in response to the modulation of an external magnetic field. The observed signal was of the order of 10−3pA, and a great deal of effort was invested into minimizing the spurious signals which can mask the magnetization-induced signal at the frequency of the modulation.
In the course of measurements at low electron densities and temperatures we encountered a signal, which would correspond to addition of more than a Bohr-magneton per electron, something that we could not explain. We started to look for possible artifacts, and indeed came to a conclusion that a part of the measured signal is unrelated to the magnetization of the 2DEG, and stems from the effect of the magnetic field on the contact resistance
of the sample. In the work presented here we concentrate on this artifact, suggest a model which captures its main features, and a way to avoid it altogether.