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Unraveling materials Berry curvature and Chern numbers from real-time evolution of Bloch states
Shin, Dongbin,Sato, Shunsuke A.,Hü,bener, Hannes,De Giovannini, Umberto,Kim, Jeongwoo,Park, Noejung,Rubio, Angel National Academy of Sciences 2019 PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES OF Vol.116 No.10
<▼1><P><B>Significance</B></P><P>It was established by Thouless, Kohmoto, Nightingale, and den Nijs in 1982 that the topology of the solid-state wavefunctions leads to quantization of transverse electrical conductivity of an insulator. This recognition has led to the development of the new field of topological materials characterized by symmetry-protected quantum numbers. Here, we propose a general and computationally efficient framework enabling one to unveil and predict materials-topological invariants in terms of physical observables, such as the bulk time-dependent current. We show how the quantized charge and spin Hall effect appears even for materials with a non-Abelian Berry phase. This dynamical approach is not necessarily restricted to density functional theory, but can be extended to other schemes and to other methods dealing with correlations explicitly.</P></▼1><▼2><P>Materials can be classified by the topological character of their electronic structure and, in this perspective, global attributes immune to local deformations have been discussed in terms of Berry curvature and Chern numbers. Except for instructional simple models, linear response theories have been ubiquitously used in calculations of topological properties of real materials. Here we propose a completely different and versatile approach to obtain the topological characteristics of materials by calculating physical observables from the real-time evolving Bloch states: The cell-averaged current density reveals the anomalous velocities that lead to the conductivity quantum. Results for prototypical cases are shown, including a spin-frozen valley Hall and a quantum anomalous Hall insulator. The advantage of this method is best illustrated by the example of a quantum spin Hall insulator: The quantized spin Hall conductivity is straightforwardly obtained irrespective of the non-Abelian nature in its Berry curvature. Moreover, the method can be extended to the description of real observables in nonequilibrium states of topological materials.</P></▼2>
Terahertz field-induced phase transition via nonlinear phonon interaction
Dongbin Shin,Angel Rubio 한국자기학회 2021 한국자기학회 학술연구발표회 논문개요집 Vol.31 No.1
Light-matter interaction has been attracted attention in the field of condensed matter physics and optics from the last century. Recent studies revealed that applying terahertz (THz) field on the material can lead the enhancement of material property or induce the phase transition. For example, high temperature superconductivity (~100K) is experimentally observed by illuminating the THz-field on the K<sub>3</sub>C<sub>60</sub> from its lower superconducting critical temperature (~30K) at the ambient condition. In our work, we investigated the THz field-induced phase transition based on the first principle calculation. At first, we show the microscopic details of THz field-induced ferroeletric phase transition in SrTiO<sub>3</sub>, which is demonstrated in the recent experiment. In second, we suggest the THz field-induced Weyl points in the trivial semimetal HgTe. Especially, we revealed that the nonlinear phonon interaction is the main mechanism of these THz field-induced phase transition. Our studies highlight that THz field can be a great tool for manipulating material properties.
Shin, Dongbin,Lee, Geunsik,Miyamoto, Youshiyuki,Park, Noejung American Chemical Society 2016 Journal of chemical theory and computation Vol.12 No.1
<P>We present methods for combining time-dependent density functional theory and the Hubbard U potential in the framework of the real-time propagation of Kohn-Sham orbitals to describe electron-atom coupled dynamics beyond the Born-Oppenheimer approximation. The time evolution of the non-commuting nonlocal operators were realized through Crank-Nicolson's inversion method and Suzuki-Trotter's split exponentiation. The electron dynamics related to the high speed motion of an alkali atom on a conjugated carbon plane is presented. The nonequilibrium charge oscillation between a metal surface and a localized atomic orbital, as modeled with graphene and Ca, is discussed.</P>
Shin Dongbin 한국물리학회 2022 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.81 No.8
Recent studies of light–matter interaction reveal that light can significantly manipulate materials’ properties. For example, recent experiments demonstrated light-induced phenomena such as light-enhanced superconductivity, ferroelectricity, topological phase transition, and light-driven quantum transport in condensed matter systems. With these experimental observations, various theoretical studies tried to provide possible microscopic mechanisms such as nonlinear phonon interaction, displacive excitation of coherent phonon, and Floquet engineering. These comprehensive experimental and theoretical studies suggested the possibility of light-controlled devices as an application. This review summarizes recently reported light-induced phenomena and related microscopic mechanisms. In addition, the numerical tools for the simulation of light-induced dynamics are introduced.
불안민감성과 불확실성에 대한 인내력 부족이 걱정 증상에 미치는 영향
신동빈 ( Dongbin Shin ),김은정 ( Eunjung Kim ) 사단법인 아시아문화학술원 2021 인문사회 21 Vol.12 No.1
본 연구는 대학생, 대학원생을 대상으로 하여 불안민감성 및 불확실성에 대한 인내력 부족과 걱정 증상 간의 관계에서, 지각된 통제감이 매개하는지 알아보는 데 연구목적이 있다. 이를 위해, 대학생 및 대학원생 252명으로 하여금 불안민감성 척도, 불확실성에 대한 인내력 부족 척도, 지각된 통제감 척도, 걱정 증상 척도 질문지를 작성하게 하였다. 구조방정식을 사용한 결과, 불안민감성 및 불확실성에 대한 인내력 부족이 걱정 증상에 미치는 영향이 지각된 통제감에 의해 완전 매개 되는 것으로 나타났다. 본 연구는 기질 변인인 불안민감성과 성향 요인인 불확실성에 대한 인내력 부족이 상호관련성을 통제한 후에도 걱정 증상에 미치는 영향력이 유의하다는 사실을 검증했다는 점에서 걱정 증상의 모형을 확장하는 데 기초를 제공한다. This study examined mediating effect of perceived control in relationships among anxiety sensitivity, intolerance of uncertainty, and worry symptoms in college and graduate students. Two hundred fifty-two undergraduate and graduate students completed Anxiety Sensitivity Scale, Intolerance of Uncertainty Scale, Anxiety Control Scale, and Worry Symptoms Scale. As a result of using the structural equation, the relationship between anxiety sensitivity and intolerance of uncertainty, and worry symptoms were fully mediated by perceived control. This study provides a basis for expanding the model of worry symptoms in that the anxiety sensitivity as a temperament variable and intolerance of uncertainty as a propensity factor has a significant effect on worry symptoms even after controlling the interrelationship.