Topological Superconductors and Dark Matter Searches in Gravitational Wave Interferometers

This work is comprised of research in two areas: superconductors and gravitational waves. Superconductors have led to novel fundamental discoveries, including new topological states. These states are robust, in that they are not altered by common changes to their environment. Here, I will introduce three studies focused on topological properties of various superconductors. First, newly proposed even-parity superconducting state in Sr$_2$RuO$_4$ introduces the emergence of topologically protected Bogoliubov Fermi surfaces. Next, I will discuss topological bands and odd-parity superconductivity in UTe$_2$, which suggest Weyl nodes and their potential topological properties. Lastly, anomalous pseudospin in non-symmorphic materials shows different symmetry properties than the usual spin-1/2 and has its applications on BiS$_2$, UPt$_3$, Fe-based superconductors, and UCoGe. LIGO and Virgo are laser interferometers designed to detect gravitational waves, enabling a variety of physical analyses. One important aspect involves measuring the spacetime volume sensitivity $\langle VT \rangle$. The researchers typically inject simulated signals to measure $\langle VT \rangle$ which is computationally expensive. I will present a machine learning method to reduce the computational cost of this process. Furthermore, these detectors can conduct dark matter searches. My research proposes a hypothesis that dark matter particles decay into gravitational waves, producing detectable blip glitches, which have traditionally been considered as noise. I will present a dimensional and data analysis to test the plausibility of my hypothesis

Group Theoretic Approach to Fermion Production

We propose a universal group theoretic description of the fermion production through any type of interaction to scalar or pseudo-scalar. Our group theoretic approach relies on the group $SU(2) \times U(1)$, corresponding to the freedom in choosing representations of the gamma matrices in Clifford algebra, under which a part of the Dirac spinor function transforms like a fundamental representation. In terms of a new $SO(3)$ ($\sim SU(2)$) vector constructed out of spinor functions, we show that fermion production mechanism can be analogous to the classical dynamics of a vector precessing with the angular velocity. In our group theoretic approach, the equation of motion takes a universal form for any system, and choosing a different type of interaction or a different basis amounts to selecting the corresponding angular velocity. The expression of the particle number density is greatly simplified, compared to the traditional approach, and it provides us with a simple geometric interpretation of the fermion production dynamics. For the purpose of the demonstration, we focus on the fermion production through the derivative coupling to the pseudo-scalar.Comment: 25 pages, 4 figures, v3: version accepted to JHEP. New Section V adde

Superconductivity of anomalous pseudospin

Spin-orbit coupling driven by broken inversion symmetry ($I$) is known to lead to unusual magnetic response of superconductors, including extremely large critical fields for spin-singlet superconductors. This unusual response is also known to appear in materials that have $I$, provided there is local $I$-breaking: fermions participating in superconductivity reside on crystal sites that lack $I$. Here we show that this unusual response exists even when the crystal sites preserve $I$. Indeed, we argue that the symmetry of Kramers degenerate fermionic pseudospin is more relevant than the local crystal site symmetry. We examine and classify non-symmorphic materials with momentum space spin-textures that exhibit an anomalous pseudospin with different symmetry properties than usual spin-1/2. We find that this anomalous pseudospin does not depend on the existence of local $I$ breaking crystal sites and it optimizes the unusual magnetic response traditionally associated with locally noncentrosymmetric superconductors, dramatically extending the range of relevant materials. We further show this anomalous pseudospin leads to fully gapped `nodal' superconductors and provides additional insight into the breakdown of Blount's theorem for pseudospin triplet superconductors. We apply our results to UPt$_3$, BiS$_2$-based superconductors, Fe-based superconductors, and paramagnetic UCoGe

Finding the distance between the Roman Pot floor and the AFP Silicon detectors

The ATLAS Forward Proton (AFP) detectors are designed for tagging of forward protons and located inside Roman Pots (RP). My task as summer student is a data analysis to measure the distance between Silicon detectors and the RP floor. For this task there are three suggested methods: tracks pointing to the floor, slope range, and shadow of station. I tried first two methods with data from AFP run 30539. The result from tracking method is 0.7mm, however the unexpected result has to be explained to fully trust this result. In the result of the slope range method, there is an impossible result. Therefore, my code for range method needs debugging in future work

Colossal flexoresistance in dielectrics

© 2020, The Author(s). Dielectrics have long been considered as unsuitable for pure electrical switches; under weak electric fields, they show extremely low conductivity, whereas under strong fields, they suffer from irreversible damage. Here, we show that flexoelectricity enables damage-free exposure of dielectrics to strong electric fields, leading to reversible switching between electrical states—insulating and conducting. Applying strain gradients with an atomic force microscope tip polarizes an ultrathin film of an archetypal dielectric SrTiO3 via flexoelectricity, which in turn generates non-destructive, strong electrostatic fields. When the applied strain gradient exceeds a certain value, SrTiO3 suddenly becomes highly conductive, yielding at least around a 108-fold decrease in room-temperature resistivity. We explain this phenomenon, which we call the colossal flexoresistance, based on the abrupt increase in the tunneling conductance of ultrathin SrTiO3 under strain gradients. Our work extends the scope of electrical control in solids, and inspires further exploration of dielectric responses to strong electromechanical fields11sci