Fermi Surface Spin Texture and Topological Superconductivity in Spin-Orbit Free Non-Collinear Antiferromagnets

We explore the relationship among the magnetic ordering in real space, the resulting spin texture on the Fermi surface, and the related superconducting gap structure in non-collinear antiferromagnetic metals without spin-orbit coupling. Via a perturbative approach, we show that a non-collinear magnetic ordering in a metal can generate a momentum-dependent spin texture on its Fermi surface, even in the absence of spin-orbit coupling, if the metal has more than three sublattices in its magnetic unit cell. Thus, our theory naturally extends the idea of altermagnetism to non-collinear spin structures. When superconductivity is developed in a magnetic metal, as the gap-opening condition is strongly constrained by the spin texture, the nodal structure of the superconducting state is also enforced by the magnetism-induced spin texture. Taking the non-collinear antiferromagnet on the kagome lattice as a representative example, we demonstrate how the Fermi surface spin texture induced by noncollinear antiferromagnetism naturally leads to odd-parity spin-triplet superconductivity with nontrivial topological properties

Essays on State Capacity and Human Capital

This dissertation consists of three chapters exploring challenges that many developing countries face in augmenting state capacity and accumulating human capital. In particular, I focus on difficulties in developing state capacity and human capital induced by political violence, natural disasters, and over-reliance on income from foreign countries. The first chapter explores the effects of losing local politicians on the fiscal and personnel capacity of local governments using the outcome of the assassination attempts on mayors in Mexico. The second chapter investigates the effects of exposure to natural disasters on birth outcomes in Indonesia, using the Indian Ocean Tsunami as a natural experiment. In the final chapter, I use a cross-country analysis to study the link between reliance on remittances and the capacity of a country to collect taxes efficiently. The first chapter investigates the effects of losing mayors to successful assassinations on the capacity of local governments. By leveraging the randomness in the outcomes of assassination attempts against mayors in Mexico in 2002-21, I find that the loss of mayors negatively affects the fiscal and personnel capacities of the local governments. Municipal tax collection decreases by 29\%. The share of expenditure on primary services falls by 3 percentage points and is crowded out toward investment in construction. Municipal workers at productive stages in their careers leave the position. The back-of-the-envelope calculation shows that wages should increase by 13\% to retain them after assassinations. Organized criminal groups take advantage of the loss of mayors by increasing their presence in municipalities with successful assassinations. The results are not explained by non-political violence, levels of economic activities, or population changes. The results speak to the significance of leaders in maintaining fiscal capacity and retaining capable personnel in the workforce even in a violent environment. In the second chapter, co-authored with Elizabeth Kayoon Hur (Michigan State University), I evaluate the effect of in-utero exposure to the 2004 Indian Ocean Tsunami on short-term childbirth outcomes in Indonesia. Exploiting variation in the timing of exposure, I find that the probability of successful pregnancies drops by 5.9 percentage points (pp), while miscarriages increase by 5.5 pp for those exposed in the earliest stage of pregnancy. I find suggestive evidence that post-disaster health investments by households may have shielded later cohorts from harmful effects. The results suggest the importance of considering fetal loss in developing countries and highlight that facilitating household investment in health through various policies may mitigate negative birth effects in the aftermath of natural disasters. The third chapter investigates the relationship between a country's reliance on remittances from abroad and its ability to collect taxes from various domestic sources. Despite the increasing flow of remittances in volume and proportion, particularly among developing countries, their role in determining the state's capacity to collect taxes has received little attention. This chapter explores the link between remittances and various tax revenue categories using country-level data. Two-way panel regressions suggest that a 1 percentage point (pp) increase in the inflow of remittances explains a 0.12 pp rise in consumption tax revenues. The same estimate derived from IV methods proxying for migrant network strength and openness of borders increases to 0.9 pp. Decomposing this result reveals that the increase in household consumption expenditure explains all of the statistical association, not the efficient tax-collecting mechanisms such as VAT. Subsample regressions by income category suggest that the association between remittances and consumption tax revenue is stronger in countries with lower income

Memory effect and phase transition in a hierarchical trap model for spin glass

We introduce an efficient dynamical tree method that enables us, for the first time, to explicitly demonstrate thermo-remanent magnetization memory effect in a hierarchical energy landscape. Our simulation nicely reproduces the nontrivial waiting-time and waiting-temperature dependences in this non-equilibrium phenomenon. We further investigate the condensation effect, in which a small set of micro-states dominates the thermodynamic behavior, in the multi-layer trap model. Importantly, a structural phase transition of the tree is shown to coincide with the onset of condensation phenomenon. Our results underscore the importance of hierarchical structure and demonstrate the intimate relation between glassy behavior and structure of barrier trees

Correlated normal state fermiology and topological superconductivity in UTe2

UTe2 is a promising candidate for spin-triplet superconductors, in which a paramagnetic normal state becomes superconducting due to spin fluctuations. The subsequent discovery of various unusual superconducting properties has promoted the use of UTe2 as an exciting playground to study unconventional superconductivity, but fathoming the normal state fermiology and its influence on the superconductivity still requires further investigation. Here, we theoretically show that electron correlation induces a dramatic change in the normal state fermiology with an emergent correlated Fermi surface (FS) driven by Kondo resonance at low temperatures. This emergent correlated FS can account for various unconventional superconducting properties in a unified way. In particular, the geometry of the correlated FS can naturally host topological superconductivity in the presence of odd-parity pairings, which become the leading instability due to strong ferromagnetic spin fluctuations. Moreover, two pairs of odd-parity channels appear as accidentally degenerate solutions, which can naturally explain the multicomponent superconductivity with broken time-reversal symmetry. Interestingly, the resulting time-reversal breaking superconducting state is a Weyl superconductor in which Weyl points migrate along the correlated FS as the relative magnitude of nearly degenerate pairing solutions varies. We believe that the correlated normal state fermiology we discovered provides a unified platform to describe the unconventional superconductivity in UTe2.Comment: 13 pages, 4 figures and 1 table in the main text, and 10 figures and 1 table in the Supplementary Informatio

Whole-genome sequencing of Listeria monocytogenes isolated from the first listeriosis foodborne outbreak in South Korea

Listeria monocytogenes is a foodborne pathogen that causes listeriosis in humans with severe symptoms. In South Korea, listeriosis had only been reported sporadically among hospitalized patients until the first foodborne outbreak occurred in 2018. In this study, a L. monocytogenes strain responsible for this outbreak (FSCNU0110) was characterized via whole genome sequencing and compared with publicly available L. monocytogenes genomes of the same clonal complex (CC). Strain FSCNU0110 belonged to multilocus sequence typing (MLST)-based sequence type 224 and CC224, and core genome MLST-based sublineage 6,178. The strain harbored tetracycline resistance gene tetM, four other antibiotic resistance genes, and 64 virulence genes, including Listeria pathogenicity island 1 (LIPI-1) and LIPI-3. Interestingly, llsX in LIPI-3 exhibited a characteristic SNP (deletion of A in position 4, resulting in a premature stop codon) that was missing among all CC224 strains isolated overseas but was conserved among those from South Korea. In addition, the tetM gene was also detected only in a subset of CC224 strains from South Korea. These findings will provide an essential basis for assessing the characteristics of CC224 strains in South Korea that have shown a potential to cause listeriosis outbreaks

Low-temperature synthesis of CuO-interlaced nanodiscs for lithium ion battery electrodes

In this study, we report the high-yield synthesis of 2-dimensional cupric oxide (CuO) nanodiscs through dehydrogenation of 1-dimensional Cu(OH)2 nanowires at 60°C. Most of the nanodiscs had a diameter of approximately 500 nm and a thickness of approximately 50 nm. After further prolonged reaction times, secondary irregular nanodiscs gradually grew vertically into regular nanodiscs. These CuO nanostructures were characterized using X-ray diffraction, transmission electron microscopy, and Brunauer-Emmett-Teller measurements. The possible growth mechanism of the interlaced disc CuO nanostructures is systematically discussed. The electrochemical performances of the CuO nanodisc electrodes were evaluated in detail using cyclic voltammetry and galvanostatic cycling. Furthermore, we demonstrate that the incorporation of multiwalled carbon nanotubes enables the enhanced reversible capacities and capacity retention of CuO nanodisc electrodes on cycling by offering more efficient electron transport paths