Millimeter wave transmission spectroscopy of two-dimensional electron and hole systems
Stone, Kristjan Jakob
Doctor of Philosophy
In order to explore how electrons and holes in 2D semiconductors behave at 3He temperatures under millimeter wave irradiation, we developed a new probe and measurement technique. Our samples are specially grown high-mobility GaAs/AlGaAs 2D electron or hole systems that have been modulation doped with Si or C respectively and etched into Hall bars. We also use microwave irradiation waveguide techniques to probe edge magnetoplasmons in 2D electron systems and find that the periodic resistance oscillations in the magnetic field are independent of the length between the leads measured. This demonstrates that the propagation of edge states is a non-local effect, contrary to previously established research. We confirm microwave induced resistance oscillations using a newly developed probe that delivers microwaves from a frequency generator down to the sample via a coax line and coplanar waveguides. Due to the low frequency range (2 -- 40 GHz) and high irradiation powers available, we are able to observe microwave induced resistance oscillations and newly revealed fractional microwave induced resistance oscillations. The probe that we develop for this new measurement makes previously unattainable non-Faraday as well as Faraday irradiation geometries accessible. In addition to measuring quantum transport, it also allows us to measure the transmission of microwaves across the sample. We establish a differential measurement technique that instantaneously removes the background signal leaving only the transmission from the 2D system, also reducing the preparation time required. This is accomplished with a gated high-mobility sample prepared to allow for microwaves to be irradiated from the back. The advantage of this new technique is that it accommodates any gated/polished sample which can be mounted on the specially designed sample holder. From this arrangement we are able to measure the cyclotron resonance transmission minima of both the 2D electron and hole systems. We can then use the known values for the effective mass and cyclotron time constant as a confirmation that our new probe can successfully make the expected measurements.
Low temperature physics; Condensed matter physics