SPEAKER: Hyunsoo Kim (Paglione)
TITLE: Electronic structure of YPtBi: transport study
ABSTRACT: Noncentrosymmetric topological semimetal YPtBi has been considered as the first realization of high spin Cooper pairing with mixed singlet and septet states. Determination of exact superconducting pairing states requires a detailed knowledge of band structure as well as Fermi surface. However, structure of Fermi surface of YPtBi is not fully known due to experimental limitations. In addition, theoretical band structure near the chemical potential has been controversial. The measurement of electrical transport is among useful probes to study the electronic structure. In this talk, the electronic structure of YPtBi will be discussed based on electrical transport measurements including resistivity and Hall effect in order to shed light on the current issues of electronic structure of YPtBi.
SPEAKER: Peng Xu (Osborn)
TITLE: Thickness Dependent Quality Factor in O2 plasma pretreated TiN film
ABSTRACT Superconducting titanium nitride (TiN) films are used in quantum computing devices because they can exhibit low microwave loss and high kinetic conductance. One of the major sources of loss is due to Two Level Systems (TLS) defects present at the interface between TiN and the substrate. Thus we pre-treated the substrate with a number of different functionalizations including O2, argon and C4H4 at two different film thicknesses (25nm and 50nm). Unexpectedly, we found a thickness dependence of internal quality factor for the pre-treated O2 films. An order of magnitude shift in internal quality factor (Qi) is shown in the experimental transmission data of the coplanar waveguide resonators. The XPS, XRD, and SIMS show that the growth, grain size and structure of film have been modified in the 25nm film because of the oxygen pretreatment. We also see a difference in the temperature dependence where quasiparticle seem to be already present in the thinner O2 film at low temperatures. This deviation could be the result of a transition to a highly disordered superconductor where the mean free path, l, is smaller than coherence length, L. A modified Mattis Bardeen theory including quasiparticle scattering fits the temperature dependence data well.