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 GaSe nanosheets
Graphene’s experimental realization kickstarted a new area of research involving the exfoliation of layered/Van der Waals materials into nanosheets and even monolayers, the fabrication of devices of this isolated nanosheets or combinations of such materials forming heterostructures and the characterization of these devices.
Our study focuses on GaSe which belongs to this category of layered materials. The unique combination of properties in this material (a band-gap of ~2 eV, relatively stable compound, high photoconductivity, the presence of Dresselhaus effective magnetic field) makes it a promising candidate for electronic, optoelectronic and spintronic applications. More specifically one of the properties of monolayer GaSe that is interesting for Spintronics applications is the anisotropic spin relaxation due to the internally present Dresselhaus effective magnetic field. This property coupled with the ability to induce a gate-tunable Rashba effective magnetic field allows for the injection and detection of spin-polarized current which is completely controlled by electric fields (no external magnetic fields). In my presentation I will talk about the unique properties of GaSe, I will present measurements regarding the electronic and optical properties of few-layer GaSe nanosheets and finally, I will discuss future work regarding our attempts to demonstrate the anisotropic spin relaxation in GaSe 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.

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