Physics 838 Seminar
04.29.2019 4:00 pm - 5:00 pm
John S. Toll Rm 1201


Speaker 1: Christos Tengeris
Advisor: I. Appelbaum
Title: Electronic, optical and spintronic properties of III-VI Van der Waals semiconductors


Graphene’s experimental realization kickstarted a new area of research involving the exfoliation of layered/Van der Waals materials into nanosheets and even monolayers which can be incorporated into the fabrication of devices of this isolated nanosheets or combination of such materials forming heterostructures.

Our study focuses on III-VI semiconductors (GaSe and InSe) which belong to this category of layered materials. The unique combination of properties in these materials (band-gap, relatively stable compound, high photoconductivity, presence of Dresselhaus effective magnetic field) makes it a promising candidate for electronic, optoelectronic and spintronic applications.
In my presentation I will talk about the fabrication process and characterization of multilayer II-VI field-effect devices and present measurements of the I-V curves, mobility, and photoconductivity for various temperatures and gate voltages obtained from these devices. Also, I will discuss future work regarding our attempts to demonstrate the anisotropic spin relaxation in monolayer III-VI semiconductors that was predicted by theory.

Speaker 2: Rui Zhang
Advisor: Ben Palmer
Title: Unexpected Behavior of Transmon Relaxation Due to Non-Equilibrium Quasiparticles
Understanding and decreasing the energy relaxation rate of transmon qubits is important for their use as qubits. One known source of relaxation is non-equilibrium quasiparticles. We have measured the relaxation time T1 of Al/AlOx/Al transmons mounted in a 3D aluminum cavity and have found that T1can increase by as much as a factor of two (up to 90 us) when increasing the temperature of the device from 20 mK to 100 mK. We will discuss our results and compare them to a model based on the behavior of non-equilibrium quasiparticles residing in regions of the transmon with slightly different superconducting energy gaps. Fits to the model allow us to extract key parameters such as the values of the superconducting energy gap and density of non-equilibrium quasiparticles in each region.