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120. Quantum Hall criticality in Floquet topological insulators

Author

Kim, Kun Woo, Bagrets, Dmitry, Micklitz, Tobias, Altland, Alexander, Kim, Kun Woo, Bagrets, Dmitry, Micklitz, Tobias, and Altland, Alexander

Abstract

The anomalous Floquet Anderson insulator (AFAI) is a two-dimensional periodically driven system in which static disorder stabilizes two topologically distinct phases in the thermodynamic limit. The presence of a unit-conducting chiral edge mode and the essential role of disorder induced localization are reminiscent of the integer quantum Hall (IQH) effect. At the same time, chirality in the AFAI is introduced via an orchestrated driving protocol, there is no magnetic field, no energy conservation, and no (Landau level) band structure. In this paper, we show that in spite of these differences the AFAI topological phase transition is in the IQH universality class. We do so by mapping the system onto an effective theory describing phase coherent transport in the system at large length scales. Unlike with other disordered systems, the form of this theory is almost fully determined by symmetry and topological consistency criteria, and can even be guessed without calculation. (However, we back this expectation by a first-principles derivation.) Its equivalence to the Pruisken theory of the IQH demonstrates the above equivalence. At the same time, it makes predictions on the emergent quantization of transport coefficients, and the delocalization of bulk states at quantum criticality which we test against numerical simulations.

Published
2020

121. Anomalous transport in a topological Wannier-Stark ladder

Author

Kim, Kun Woo, Andreanov, Alexei, Flach, Sergej, Kim, Kun Woo, Andreanov, Alexei, and Flach, Sergej

Abstract

A dc (e.g., electric) field with commensurate lattice direction turns a single-particle band structure in d = 3 dimensions into an infinite set of equally spaced irreducible (d - 1) = 2-dimensionalWannier-Stark (WS) band structures that are spatially localized along the field direction. Particle transport is expected to be suppressed once the WS bands are gapped in energy. The topological character of the irreducible band structure leads to one-dimensional sets of boundary states which fill the energy gaps. As a result, eigenmodes are smoothly connected in energy and space and yield anomalous particle transport throughout the ladder. The number of chiral boundary modes can be tuned by the dc field strength and manifests through the distribution of dissipated energy and spatial motion, and the temperature dependence of angular momentum carried by particles.

Published
2020

130. Development of a test method and experimental study on cable unwinding.

Author

Kang, Ji-Heon, Kim, Kun-Woo, Lee, Jae-Wook, Cho, Yong-Jae, and Jang, Jin-Seok

Abstract

In addition to the textile industry, unwinding of cable or fiber is used in various fields such as electronics, communication, and guided weapons. The cable released from the package exhibit a complicated behavior, entailing a combination of rotational and translational motion. This causes problems such as entangling and fracture. Therefore, it is necessary to study boundary and adhesion conditions to prevent unwinding failure. In this study, an experimental device for the analysis of cable unwinding was developed, and unwinding behavior was analyzed experimentally under various unwinding conditions. The experimental device comprises a jig for high-speed camera measurements, control device, and cable unwinding device. Cable behavior was analyzed according to the unwinding velocity and the distance between the fiber package and the point where the fiber was released. In addition, unwinding behavior with respect of the tension acting on the cable was analyzed experimentally by applying the adhesive. [ABSTRACT FROM AUTHOR]

Published
2021
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131. Tumour-infiltrating bystander CD8+T cells activated by IL-15 contribute to tumour control in non-small cell lung cancer

Author

Leem, Galam, Jeon, Minwoo, Kim, Kun Woo, Jeong, Seongju, Choi, Seong Jin, Lee, Yong Joon, Kim, Eui-Soon, Lee, Jae-Ik, Ha, Seung Yeon, Park, Su-Hyung, Shim, Hyo Sup, Lee, Jin Gu, Kang, Shin Myung, and Shin, Eui-Cheol

Abstract

BackgroundTumour-unrelated, virus-specific bystander CD8+T cells were recently shown to be abundant among tumour-infiltrating lymphocytes (TILs). However, their roles in tumour immunity have not been elucidated yet.MethodsWe studied the characteristics of bystander CD8+TILs from non-small cell lung cancer (NSCLC) tissues (N=66) and their activation by interleukin (IL)-15 to repurpose them for tumour immunotherapy.ResultsWe show that bystander CD8+TILs specific to various viruses are present in human NSCLC tissues. We stimulated CD8+TILs ex vivo using IL-15 without cognate antigens and found that IL-15 treatment upregulated NKG2D expression on CD8+TILs, resulting in NKG2D-dependent production of interferon (IFN)-γ (p=0.0006). Finally, we tested whether IL-15 treatment can control tumour growth in a murine NSCLC model with or without a history of murine cytomegalovirus (MCMV) infection. IL-15 treatment reduced the number of tumour nodules in the lung only in mice with MCMV infection (p=0.0037). We confirmed that MCMV-specific bystander CD8+TILs produced interferon (IFN)-γ after IL-15 treatment, and that IL-15 treatment in MCMV-infected mice upregulated tumour necrosis factor-α and IFN-γ responsive genes in tumour microenvironment.ConclusionThus, the study demonstrates that bystander CD8+TILs can be repurposed by IL-15 for tumour immunotherapy.

Published
2022
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136. Korean physicians’ attitudes toward the prenatal screening for fetal aneuploidy and implementation of non-invasive prenatal testing with cell-free fetal DNA

Author

Kim, Soo Hyun, primary, Kim, Kun Woo, additional, Han, You Jung, additional, Lee, Seung Mi, additional, Lee, Mi-Young, additional, Shim, Jae-Yoon, additional, Cho, Geum Joon, additional, Lee, Joon Ho, additional, Oh, Soo-young, additional, Kwon, Han-Sung, additional, Cha, Dong Hyun, additional, and Ryu, Hyun Mee, additional

Published
2018
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143. Electronic States in Disordered Topological Insulators

Author

Kim, Kun Woo, Kim, Kun Woo, Kim, Kun Woo, and Kim, Kun Woo

Abstract

We present a theoretical study of electronic states in topological insulators with impurities. Chiral edge states in 2d topological insulators and helical surface states in 3d topological insulators show a robust transport against nonmagnetic impurities. Such a nontrivial character inspired physicists to come up with applications such as spintronic devices [1], thermoelectric materials [2], photovoltaics [3], and quantum computation [4]. Not only has it provided new opportunities from a practical point of view, but its theoretical study has deepened the understanding of the topological nature of condensed matter systems. However, experimental realizations of topological insulators have been challenging. For example, a 2d topological insulator fabricated in a HeTe quantum well structure by Konig et al. [5] shows a longitudinal conductance which is not well quantized and varies with temperature. 3d topological insulators such as Bi2Se3 and Bi2Te3 exhibit not only a signature of surface states, but they also show a bulk conduction [6]. The series of experiments motivated us to study the effects of impurities and coexisting bulk Fermi surface in topological insulators. We first address a single impurity problem in a topological insulator using a semiclassical approach. Then we study the conductance behavior of a disordered topological-metal strip where bulk modes are associated with the transport of edge modes via impurity scattering. We verify that the conduction through a chiral edge channel retains its topological signature, and we discovered that the transmission can be succinctly expressed in a closed form as a ratio of determinants of the bulk Green's function and impurity potentials. We further study the transport of 1d systems which can be decomposed in terms of chiral modes. Lastly, the surface impurity effect on the local density of surface states over layers into the bulk is studied between weak and strong disorder

Published
2014

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