10 research outputs found
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 SrRuO introduces the emergence of topologically protected Bogoliubov Fermi surfaces. Next, I will discuss topological bands and odd-parity superconductivity in UTe, 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, UPt, 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 . The researchers typically inject simulated signals to measure 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 , 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 () 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
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Superconductivity of anomalous pseudospin
Spin-orbit coupling driven by broken inversion symmetry () 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 , provided there is local
-breaking: fermions participating in superconductivity reside on crystal
sites that lack . Here we show that this unusual response exists even when
the crystal sites preserve . 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 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, BiS-based superconductors, Fe-based
superconductors, and paramagnetic UCoGe
Stabilizing Even-Parity Chiral Superconductivity in SrRuO
Strontium ruthenate (SrRuO) has long been thought to host a
spin-triplet chiral -wave superconducting state. However, the singletlike
response observed in recent spin-susceptibility measurements casts serious
doubts on this pairing state. Together with the evidence for broken
time-reversal symmetry and a jump in the shear modulus at the
superconducting transition temperature, the available experiments point towards
an even-parity chiral superconductor with -like
symmetry, which has consistently been dismissed based on the
quasi-two-dimensional electronic structure of SrRuO. Here, we show how
the orbital degree of freedom can encode the two-component nature of the
order parameter, allowing for a local orbital-antisymmetric spin-triplet state
that can be stabilized by on-site Hund's coupling. We find that this exotic
state can be energetically stable once a complete, realistic
three-dimensional model is considered, within which momentum-dependent
spin-orbit coupling terms are key. This state naturally gives rise to
Bogoliubov Fermi surfaces.Comment: 6+10 pages, 5 figure
Search for eccentric black hole coalescences during the third observing run of LIGO and Virgo
Despite the growing number of confident binary black hole coalescences observed through gravitational waves so far, the astrophysical origin of these binaries remains uncertain. Orbital eccentricity is one of the clearest tracers of binary formation channels. Identifying binary eccentricity, however, remains challenging due to the limited availability of gravitational waveforms that include effects of eccentricity. Here, we present observational results for a waveform-independent search sensitive to eccentric black hole coalescences, covering the third observing run (O3) of the LIGO and Virgo detectors. We identified no new high-significance candidates beyond those that were already identified with searches focusing on quasi-circular binaries. We determine the sensitivity of our search to high-mass (total mass M>70 M⊙) binaries covering eccentricities up to 0.3 at 15 Hz orbital frequency, and use this to compare model predictions to search results. Assuming all detections are indeed quasi-circular, for our fiducial population model, we place an upper limit for the merger rate density of high-mass binaries with eccentricities 0<e≤0.3 at 0.33 Gpc−3 yr−1 at 90\% confidence level
Search for gravitational-lensing signatures in the full third observing run of the LIGO-Virgo network
Gravitational lensing by massive objects along the line of sight to the source causes distortions of gravitational wave-signals; such distortions may reveal information about fundamental physics, cosmology and astrophysics. In this work, we have extended the search for lensing signatures to all binary black hole events from the third observing run of the LIGO--Virgo network. We search for repeated signals from strong lensing by 1) performing targeted searches for subthreshold signals, 2) calculating the degree of overlap amongst the intrinsic parameters and sky location of pairs of signals, 3) comparing the similarities of the spectrograms amongst pairs of signals, and 4) performing dual-signal Bayesian analysis that takes into account selection effects and astrophysical knowledge. We also search for distortions to the gravitational waveform caused by 1) frequency-independent phase shifts in strongly lensed images, and 2) frequency-dependent modulation of the amplitude and phase due to point masses. None of these searches yields significant evidence for lensing. Finally, we use the non-detection of gravitational-wave lensing to constrain the lensing rate based on the latest merger-rate estimates and the fraction of dark matter composed of compact objects
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