Band Gap Closing in a Synthetic Hall Tube of Neutral Fermions

We report the experimental realization of a synthetic three-leg Hall tube with ultracold fermionic atoms in a one-dimensional optical lattice. The legs of the synthetic tube are composed of three hyperfine spin states of the atoms, and the cyclic inter-leg links are generated by two-photon Raman transitions between the spin states, resulting in a uniform gauge flux $\phi$ penetrating each side plaquette of the tube. Using quench dynamics, we investigate the band structure of the Hall tube system for a commensurate flux $\phi=2\pi/3$. Momentum-resolved analysis of the quench dynamics reveals that a critical point of band gap closing as one of the inter-leg coupling strengths is varied, which is consistent with a topological phase transition predicted for the Hall tube system.Comment: 8 pages, 8 figure

그래핀에 의해 유도된 표면 재구성에 대한 라만 분광 연구

학위논문 (석사)-- 서울대학교 대학원 : 화학부 물리화학전공, 2015. 8. 홍병희.The surface morphology of copper (Cu) often changes during graphene synthesis by chemical vapor deposition (CVD)the change is attributed to the thermal expansion coefficient mismatch between graphene and Cu. However, the obvious relationship between the reconstructed Cu surface and graphene is not totally understood yet. Here we synthesized graphene with different layer numbers using a CVD system by controlling the gas flow and time. Atomic force microscopy (AFM) images and the Raman G and 2D peaks show that Cu step edges became noticeably broader with increasing graphene layer number. Furthermore, ?ω_G??ω_2D plot indicates that the biaxial compressive strain on monolayer graphene was higher than that on bi/trilayer graphene, which agrees overall with topographic AFM images. Our results suggest that stress relaxation from the less strained bi/trilayer graphene crucially affects Cu surface reconstruction.Contents Abstract 1 Contents 2-3 List of Figures 4-6 List of Tables and Schemes 7 Chapter 1. Introduction 1.1 Brief Introduction of Graphene 9 1.2 Synthesis of Graphene 14 1.3 Interaction between graphene and substrate. 17 1.4 Raman Spectroscopy in Graphene 19 1.4.1 Characterizing the number of layers 1.4.2 Estimation of Charge Doping on Graphene 1.4.3. Estimation of Strain on Graphene Chapter 2. Synthesis of Graphene on Cu Foil and Morphology Evolution 2.1 Synthesis of Graphene on Cu Foil 29 2.2 Morphology Change of the Cu Surface 32 2.3 Atomic Force Microscopy 35 2.4 Discussion 38 Chapter 3. Raman Spectroscopy Study 3.1 Characterizing the number of layers of graphene 42 3.2 Strain estimation via peak shift 50 3.3 Estimation of charge doping on graphene 55 3.4 Separation of the strain from charge doping effect 61 3.5 Conclusion 64Maste

Double resonance of Raman transitions in a degenerate Fermi gas

We measure momentum-resolved Raman spectra of a spin-polarized degenerate Fermi gas of $^{173}$Yb atoms for a wide range of magnetic fields, where the atoms are irradiated by a pair of counterpropagating Raman laser beams as in the conventional spin-orbit coupling scheme. Double resonance of first- and second-order Raman transitions occurs at a certain magnetic field and the spectrum exhibits a doublet splitting for high laser intensities. The measured spectral splitting is quantitatively accounted for by the Autler-Townes effect. We show that our measurement results are consistent with the spinful band structure of a Fermi gas in the spatially oscillating effective magnetic field generated by the Raman laser fields.Comment: 7 pages, 6 figure

Creutz ladder in a resonantly shaken 1D optical lattice

We report the experimental realization of a Creutz ladder for ultracold fermionic atoms in a resonantly driven 1D optical lattice. The two-leg ladder consists of the two lowest orbital states of the optical lattice and the cross inter-leg links are generated via two-photon resonant coupling between the orbitals by periodic lattice shaking. The characteristic pseudo-spin winding structure in the energy bands of the ladder system is demonstrated using momentum-resolved Ramsey-type interferometric measurements. We discuss a two-tone driving method to extend the inter-leg link control and propose a topological charge pumping scheme for the Creutz ladder system. ©2020 The Author(s). Published by IOP Publishing Ltd on behalf of the Institute of Physics and Deutsche Physikalische Gesellschaf

Realization of a cross-linked chiral ladder with neutral fermions in an optical lattice by orbital-momentum coupling

We report the experimental realization of a cross-linked chiral ladder with ultracold fermionic atoms in an optical lattice. In the ladder, the legs are formed by the orbital states of the optical lattice and the complex inter-leg links are generated by the orbital-changing Raman transitions that are driven by a moving lattice potential superimposed onto the optical lattice. The effective magnetic flux per ladder plaquette is tuned by the spatial periodicity of the moving lattice, and the chiral currents are observed from the asymmetric momentum distributions of the orbitals. The effect of the complex cross links is demonstrated in quench dynamics by measuring the momentum dependence of the inter-orbital coupling strength. We discuss the topological phase transition of the chiral ladder system for the variations of the complex cross links.Comment: 8 pages, 8 figure

Comparison of Oral Sulfate Solution and Polyethylene Glycol Plus Ascorbic Acid on the Efficacy of Bowel Preparation

Background/Aims The quality of bowel preparation is one of the quality indicators for colonoscopy. The aim of this study was to compare the efficacy of oral sulfate solution (OSS) and polyethylene glycol plus ascorbic acid (PEG-AA) for bowel preparation. Methods The study involved 167 patients who underwent diagnostic colonoscopies. Inadequate bowel preparation was defined as any score of ≤1 in each colon section based on the Boston Bowel Preparation Scale. Multivariate logistic regression was used to compare the efficacy of OSS and PEG-AA. Subgroup analyses were performed based on patient characteristics. Results Overall, 106 (63.5%) patients received OSS, and 61 (36.5%) patients received PEG-AA. The rate of inadequate bowel preparation was 12.3% in patients receiving OSS and 32.8% in patients receiving PEG-AA (p=0.001). OSS (odds ratio [OR] = 0.26; p=0.003) and morning examination (OR=0.11; p=0.038) were significantly associated with efficient bowel preparation. The efficacy of OSS compared with PEG-AA was only significant in patients ≥50 years of age vs. <50 years of age (OR=0.13; p=0.001 vs. OR=0.96; p=0.959) and female vs. male patients (OR=0.06; p=0.002 vs. OR=0.58; p=0.339). Conclusions OSS was significantly more efficient for bowel preparation than PEG-AA, especially in patients ≥50 years of age and female patients. Morning examination led to a good quality of bowel preparation, irrespective of the preparation regimen

A Case of Hypertrophic Osteoarthropathy Associated with Epithelioid Hemangioendothelioma

Epithelioid hemangioendothelioma is a rare vascular tumor, which occurs in the lung, liver, bone, and soft tissue. Hypertrophic osteoarthropathy is a syndrome characterized by subperiosteal new bone formation, joint effusion and clubbing, and may be associated with cyanotic heart disease, chronic pulmonary disease, liver disease, and other miscellaneous diseases. The activation of endothelium and platelets has been suggested to be involved in the development of hypertrophic osteoarthropathy. We report a rare case of hypertrophic osteoarthropathy, which developed in association with hepatic epithelioid hemangioendothelioma with pulmonary metastasis. We also discuss the role of vascular endothelial growth factor in its pathogenesis