Ewha Physics Colloquium

This Physics colloquium is co-organized by the Department of Physics and the Center for Quantum Nanoscience.
Due to the COVID-19 situation, this colloquium series will be done online via Zoom.

To check details, visit the Ewha Physics Department page

Location of the colloquium: Science Building A, room B101, Ewha Womans University

[Ewha Physics Department Colloquium Zoom information]

Zoom link

Passcode: 331732

2022 Schedule

2022.11.30, 5:00~6:00pm (KST)
Phd Candidate
Ewha Womans University
TBA
2022.11.23, 5:00~6:00pm (KST)
Yong-Hyun Kim
KAIST
Solving Triboelectricity
2022.11.16, 5:00~6:00pm (KST)
Jaeyong Kim
Hanyang University
Recent Studies on Synthesis and Structures of Metal Hydrides under Ultra-high Static and Dynamic Pressures Aiming for High Tc
2022.11.09, 5:00~6:00pm (KST)
Hosung Seo
Ajou University
First-principles investigation of quantum defects in two-dimensional hexagonal boron nitride
2022.11.02, 5:00~6:00pm (KST)
Gil-Ho Lee
POSTECH
Engineering graphene Josephson junction for sensitive photon detector
2022.10.26, 5:00~6:00pm (KST)
Eun-Ah Kim
Cornell University / Ewha Womans University
Machine Learning Quantum Emergence
2022.10.05, 5:00~6:00pm (KST)
Young-Sik Ra
KAIST
Scalable generation of quantum entanglement in ultrashort pulses
2022.09.28, 5:00~6:00pm (KST)
Hyunjung Kim
Sogang University
Ultrafast Phase Transformation Study using Synchrotrons and X-ray Free Electron Lasers
2022.09.21, 5:00~6:00pm (KST)
Noejung Park
UNIST
Real-time quantum dynamics of condensed matters : nonlinear optical properties and Berry curvature family
2022.09.14, 5:00~6:00pm (KST)
Aron Walsh
Imperial College London / Ewha Womans University
Sustainable Materials to Power the Future
2022.09.07, 5:00~6:00pm (KST)
Bogeun Gwak
Dongguk University
볼 수 없는 천체, 블랙홀을 찾아서 (Find a black hole, a celestial body that you can't see)
2022.06.08, 5:00~6:00pm (KST)
Miri Seo
Ewha Womans University
연구실에서 사용되는 질량 센서 데이터, 유해 화합물, 그래핀 이미지 분류를 위한 인공지능의 활용
2022.05.25, 5:00~6:00pm (KST)
Chirlmin Joo
TU Delft
Next-generation single-molecule biophysics
2022.05.18, 5:00~6:00pm (KST)
Tae jeong Kim
Hangyang University
젭토스페이스로의 여행 (Aventure to Zeptospace)
2022.05.11, 5:00~6:00pm (KST)
Kevin Insik Hahn
Center for Exotic Nuclear Studies (CENS)
Search for the origin of the Universe's heavy elements
2022.05.04, 5:00~6:00pm (KST)
Jun Sung Kim
POSTECH
When electronic band topology meets magnetism

Electronic band topology in solids has become one of the central issues in condensed matter physics in the last decade. When low energy electronic structure possesses topologically nontrivial band contact points or lines, electronic transport properties are expected to show unusual electromagnetic responses. Particularly, when combined with magnetism, topological band degeneracy can be readily tuned by spin configuration or orientation, offering an efficient magnetic control of electronic conduction. In this talk, I will briefly review the current understanding of magnetotransport properties of topological magnets and introduce van der Waals (vdW) magnets where combination of magnetism, spin-orbit interaction, and orbital-driven topological band degeneracy produces large magnetotransport responses and magnetic tunability [1–3]. The unique transport properties demonstrate that topological vdW magnets have great potential for realizing novel spin-dependent electronic functionalities, which may be suitable for spintronic applications.

[1] K.Kim, et al. Nat. Mater. 17. 794 (2018).
[2] J. Seo, et al. Sci. Adv. 6. 8912 (2020).
[3] J. Seo et al. Nature 599, 576–581 (2021).

2022.04.27, 5:00~6:00pm (KST)
Sang Yun Lee
GIST
고체 점결함을 이용한 양자정보 연구
2022.04.13, 5:00~6:00pm (KST)
Junki Kim
SKKU
Building a quantum computer with trapped ion qubits

Abstract:

An ion trap is an exotic quantum system which reveals novel quantum phenomena and h as become one of the leading quantum computing platforms. Its promising features include long qubit coherence time, low SPAM (state-preparation and detection) error, high g ate-fidelity, and all-to-all qubit connectivity. Building such a system requires deep understanding on underlying physics as well as systematic engineering approach. This talk will c over fundamental ideas of the trapped-ion based quantum computing and recent efforts on building a highly engineered device. The prospect on scaling trapped-ion devices will be discussed as well.

2022.04.06, 5:00~6:00pm (KST)
Andreas Heinrich
IBS Center for Quantum Nanoscience, Ewha Womans University
Investigating Individual Quantum Spins on Surfaces with Scanning Tunneling Microscopy

Abstract:
There is a strong international research effort in the area of quantum information science. Here, the concepts of quantum coherence, superposition and entanglement of quantum states are exploited. These concepts were originally shown with photons as well as atoms and ions in vacuum traps. Over the past two decades, many advances at studying such quantum coherence in solid-state and molecular architectures have evolved [1]. We will begin with a general introduction into quantum coherence in two-level systems and investigate a conceptually simple algorithm for a quantum computation. We will highlight a couple of experimental realizations in the solid-state that allow the quantum-coherent control of individual quantum bits (qubits). In essence, this type of research fulfills the dreams of the founders of quantum mechanics some 100 years ago, who had to think of those experiments only as Gedankenexperiments.

In the second half of the talk we will switch to my own research efforts in Scanning Tunneling Microscopy (STM). STM enables the study of surfaces with atomic-scale spatial resolution and offers the ability to study individual atoms and molecules on surfaces. Here at Ewha, we have one of the world’s best facilities for such studies. STM can also be used to move atoms with atomic-scale precision, which enables us to build engineered nanostructures where each atom is in the exactly correct place.

In order to study qubits with STM, we recently learned how to combine STM with electron spin resonance [2]. Spin resonance gives us the means to quantum-coherently control an individual atomic or molecular spin on a surface. Using short pulses of microwave radiation enables us to perform qubit rotations and learn about the quantum coherence times of our spins.

1. Andreas J. Heinrich, William D. Oliver, Lieven M. K. Vandersypen, Arzhang Ardavan, Roberta Sessoli, Daniel Loss, Ania Bleszynski Jayich, Joaquin Fernandez-Rossier, Arne Laucht, Andrea Morello, “Quantum-coherent nanoscience”, Nat. Nanotechnol., 16, 1318-1329 (2021).

2. Susanne Baumann, William Paul, Taeyoung Choi, Christopher P. Lutz, Arzhang Ardavan, Andreas J. Heinrich, “Electron Paramagnetic Resonance of Individual Atoms on a Surface”, Science 350, 417 (2015).

Support from Institute for Basic Science (IBS-R027-D1) is gratefully acknowledged.

2022.03.30, 5:00~6:00pm (KST)
박재홍 교수
Ewha Womans University
Role of Crystalline-Domains on Ultrafast Polaron Generation in Conjugated Polymers
2022.03.23, 5:00~6:00pm (KST)
조연정 교수
Kyungpook National University
위상물질의 양자진동과 이상 홀효과
2022.03.16, 5:00~6:00pm (KST)
노광동 교수
Ewha Womans University
The Next Generation of Photonic Sources – Light-Emitting Devices

2021 Schedule

2021.12.08, 6:15~6:40pm (KST)
최규리
Ewha Womans University
Excited state nature of epsilon-near-zero molecule and PL lifetime of fluorophore nearby epsilon-near-zero film

Epsilon-near-zero (ENZ) molecule belongs mainly to polymethine structure. By tuning excited state nature of ENZ molecule it is identified that a strong donor structure results in prominent ENZ property. Photo-luminescence lifetime is related to radiative and non-radiative decay rate, which can be tuned by dielectric spectrum associated with ENZ response of organic molecular film. When P3HT fluorophore was placed nearby 5nm and 20nm thick polymethine film, the change of PL lifetime shows opposite behavior.

2021.12.08, 5:50~6:15pm (KST)
정혜리
Ewha Womans University
Growth and characterization of halide perovskite single crystals for photodetector applications

유무기 복합 할로겐화물로 구성된 하이브리드 페로브스카이트 물질은 뛰어난 광전기적 특성을 지니고 있으며 이를 바탕으로 태양전지, 발광 다이오드, 광검출기 등 다양한 소자로의 응용 가능성을 가져 최근 주목을 받고 있다. 다양한 형태의 페로브스카이트 물질 중에서도 페로브스카이트 단결정 형태는 물성에 영향을 줄 수 있는 그레인 경계가 없고 페로브스카이트 물질의 큰 문제점 중 하나인 안정성이 다른 형태보다 뛰어나 물질의 본질적인 정보를 제공할 수 있다. 페로브스카이트 물질의 에너지 준위와 밴드 밴딩, 그리고 수송 특성은 소자 작동 및 효율에 직접적인 관련이 있다. 따라서 페로브스카이트 단결정을 이용하여 물질의 핵심 특성을 이해하는 것은 고효율 소자 디자인을 제시하는 데 도움이 될 수 있다.

먼저, CH3NH3PbX3 (X=I, Br, Cl) 페로브스카이트 단결정을 성장시키고 성장시킨 결정의 결정성을 파악하여 단결정임을 확인하였다. 물질의 반도체 특성을 이해하기 위해 에너지 준위에 관련된 변수를 조사하였다. 광발광 스펙트럼을 사용하여 페로브스카이트 단결정의 밴드갭 에너지를 확인하였고 캘빈 탐침 현미경을 사용하여 결정 표면의 표면 전기적 특성을 공간적으로 이미지화하였다. 표면의 일함수 분포를 공간적으로 확인하여 국소 영역에서 열화 현상과 열화 물질에 따른 표면 및 일함수 변화를 관찰하였다. 반도체 특성은 국소 열화 현상으로 생성된 열화 물질에 의해 조절될 수 있으며 일함수 분포의 분해 과정을 통해 열화 작용을 이해하고 이로 인해 생성된 물질을 파악하였다. 더불어 염화물 페로브스카이트 단결정에서 다른 할로겐 물질 기반 페로브스카이트 물질들과는 다르게 저온에서 여기자 현상이 발생하는 것을 확인하였다. 온도에 따른 수송자와 여기자 비율 계산을 통해 저온에서의 여기자 존재의 가능성을 제시하였고 레이저 파워 대비 발광 세기 분석을 통해 자유 여기자와 구속 여기자를 구분하였다.

나아가 브롬화물과 염화물 페로브스카이트 단결정에서 다양한 전극 소재와 전자 수송을 향상시키고 정공 수송을 저해하는 TiO2를 이용하여 한쪽 수송자가 우세한 소자 구조를 형성하고 구조에 따른 수송 특성을 파악하고자 하였다. 단결정의 밴드갭보다 낮은 에너지를 가지는 적색광과 높은 에너지를 가지는 근자외 청색광 모두에서 광전류가 형성되었다. 모든 구조에서 두 빛을 이용한 광보조 켈빈 탐침 현미경 측정을 통한 밴드 밴딩 현상을 분석하였고 빛의 파장에 따른 전하 수송 메커니즘을 이해하였다. 특히 빛의 에너지에 따른 여기 현상의 차이에 의해 물질 내 트랩의 존재를 간접적으로 확인하였고 이러한 빛에 따른 전기적 특성을 바탕으로 광검출기로서의 가능성을 확인하였다. 이 발표에서는 하이브리드 페로브스카이트 단결정을 이용하여 물질 고유의 광전자 특성을 이해하고 이를 바탕으로 광검출기를 제작하여 광전하 수송 메커니즘에 대해 보고한다.

2021.12.08, 5:25~5:50pm (KST)
김민재
Ewha Womans University
Linear and nonlinear optical properties of organic epsilon-near-zero films

Optical epsilon-near-zero (ENZ) material refers to an optical medium where real part of dielectric permittivity approaches to zero in optical spectral range. An anisotropic squaraine thin film was introduced to study anisotropic ENZ property by use of spectroscopic ellipsometry and prism coupling. Furthermore, second order nonlinear optical property of isotropic squaraine thin film is studied by Mach-Zehnder (MZ) interferometry. In particular, electro-optic (EO) modulation taking place at the surface of isotropic ENZ film was measured. In order to relate EO signal with ENZ response of thin film, six different wavelengths are adopted in MZ interferometer. Pockels coefficient was measured to be -150pm/V on resonance and -20pm/V off resonance.

2021.12.08, 5:00~5:25pm (KST)
권소영
Ewha Womans University
이종구조 계면에서 일어나는 전하 및 에너지 전달

대부분의 전기/광전자소자들은 두 개 이상의 물질을 적층해서 만드는 이종구조로 이루어진다. 그 이유는 계면의 에너지 밴드 배열에 따라 전하 수송과 재결합과정을 제어하는 일이 가능하기 때문이다. 따라서, 반도체 물리에서는 이종구조 계면에서 일어나는 물리현상을 이해하기 위하여 많은 이론과 실험 방법들은 개발하고 있다. 본 발표에서는 계면에서 일어나는 전하 및 에너지 수송 과정에 대한 연구 결과를 다루고자 한다. 전하 수송은 전자 주개와 받개 사이의 알짜 전하 밀도의 변화를 만들지만, 에너지 수송은 전자와 홀이 함께 수송되므로 전자 밀도의 변화가 없다. 2차원 반도체, 유기 반도체, 금속을 이용하여 제작한 이종구조의 계면에서 일어나는 현상을 광학적 전기적 특성분석을 통하여 살펴볼 것이다.

2021.12.01, 5~6pm (KST)
Prof. WU, Jeong-Weon
Ewha Womans University
Light and medium

Light propagates from vacuum to electromagnetic waves; when there is a medium, various optical phenomena appear due to the interaction between electromagnetic waves and mediums.We introduce light modulation, hologram, razing, nonlinear optics, hyperbolic dispersion, etc. that occur in optical medium such as polymer thin film, liquid crystal, photonic crystal, metamaterial.

2021.11.24, 5~6pm (KST)
Prof. Kang-Hun Ahn
Chungnam National University

Human hearing has a very surprising ability that can not be followed by advanced technology; the smallest and loudest sounds that can be heard have about a trillion times the energy difference. The frequency resolution is excellent, so the frequency difference of about 4Hz is divided into ears. More surprising is that you can understand where there is a louder noise than the sound of the horse, and you can sense the direction of the sound and listen to one of the words of many people. There has been a lot of effort to understand the principle of hearing, but it has not yet been fully understood. In this lecture, it will be shown that creating artificial neural networks that mimic human hearing and learning machines as humans learn, they have surprisingly human auditory characteristics.

2021.11.17, 5~6pm (KST)
Prof. Doohee Cho
Yonsei University

Electron quantum tunneling has been widely employed to investigate atomic-scale surface structures, as well as electronic structures in condensed matter physics. Four decades ago, in 1981, Binning and Rohrer invented a new electron microscope, called a scanning tunneling microscope (STM), in which electrons tunnel across a vacuum barrier between a surface and a scanning tip. In the works that followed, it was demonstrated that the STM empowers not only visualizing but also manipulating the atomic and electronic structure of surfaces in the atomic-scale. Since then, STM has become indispensable for investigating the local electronic structure of quantum materials. In this talk, a brief summary of the fundamentals of STM will be given, including basic principles of operation and experimental results on exotic quantum phenomena. In addition, I will introduce our recent research achievements using a shot-noise STM. This newly developed tool provides detailed insight into the charge dynamics hidden in the conventional STM signal.

2021.11.10
17~18 (KST)
Prof. Daniela Petti
Politecnico di Milano
Nanoscale engineered spin textures for magnonics

ASpin wave are propagating perturbation in the spin lattice of ordered magnetic materials. Currentsof quanta of spin waves, called magnons,can transport energy and angularmomentum without Joule losses. Magnonics, which relies on the use of spin waves for information processing, holds promises as an emergingtechnology for highly efficient computingplatforms. However, controlling spin waves at the nanoscale, crucial for the realization of magnonic nanodevices, is extremely challenging due to the difficulty in controlling the nanoscopic magnetic properties via conventional techniques. Recently, we demonstrated a new technique for creating reconfigurable magnonic structures by performing a highly localized field cooling with the hot tip of a scanning probe microscope, in an exchange biased system, comprising a ferromagnet and an antiferromagnet. In such structures, the spin-wave excitation and propagation can be spatially controlled with no need for external fields1.

In this presentation, I will first report on a strategyfor stabilizing complexmultidimensional spin textures ranging from 2D domains with tailored spin configuration, to 1D magneticdomain walls, to 0D tailoredtopological solitons with deterministically controlled chirality, position and vorticity2.

I will then demonstrate that such engineered spin textures can be used effectively as waveguides and controlled sources of propagating spin waves. In particular, I will show the channelling and steeringof propagating spin waves in arbitrarily shaped nanomagnonic waveguides based on domain walls, and a prototypic nanomagnonic circuit based on twoconverging waveguides, allowingfor the interference of confined spin-waves modes3.

Finally, I will presentan optically-inspired platformrealized by patterning tailored nanoscale spin textures in an exchange biased synthethic antiferromagnet (SAF). By coupling radiofrequency magneticfields with engineered magnonic nanoantennas consisting of nanoscale spin textures, we demonstrated nanoscalespatial shaping of propagating wavefronts, and the generation of robust multibeaminterference patterns with short- wavelength spin waves4. The ability to control magnons via nanoscale-designed spin textures opens-up a plethora of exciting possibilities for the realization of energy-efficient digital and analogcomputing platforms.

[1] E. Albisetti et al., Nat. Nanotechnol. 11 (2016), 545–551

[2] E. Albisetti, et al., Applied Physics Letters, 113 162401 (2018).

[3] E. Albisetti, et al., Commun. Phys. 1(2018), 56.

[4] E. Albisetti et al., Adv. Mater. 32, 2070063 (2020).

2021.10.27
17~18 (KST)
Prof. Jaehoon Jung
POSTECH
Artificial intelligence in physics with examples

Abstract:

Artificial intelligence (AI) has proven to be an efficient complimentary/alternative research method in various scientific disciplines. It is now an essential tool in the discipline of physics and has been successfully used to analyze complex physical phenomena (e.g. the Higgs particle discovery). The successful application of AI is contingent on the availability of the large size of available data. In other words, AI is the technique that could extract physically meaningful patterns from big data, which is big enough for knowledge extraction and reproduction of the desired underlying phenomena. In this talk, we use several different types of data such as images, signals, music, etc. and explain how these types of data are used with AI and provide underlying physics. This talk is designed as an introductory talk and will use specific examples for explanations.

2021.10.06
17~18 (KST)
Prof. Yung Kyung Park
Ewha Womans University
색온도 (color temperature)

Abstract: 색온도는 특정한 빛의 색을 나타낸다. 조명에서의 색온도와 사람에게 미치는 영향에 대해 알아보고 화질에서 색온도의 중요성을 알아보고자 한다.

2021.09.15
17~18 (KST)
Prof. Chunglee Kim
Ewha Womans University
Multi-signal astronomy, Hubble constants, cosmic dark energy
(다중신호 천문학, 허블 상수, 우주 암흑 에너지)
2021.09.15
17~18 (KST)
Prof. Chunglee Kim
Ewha Womans University
다중신호 천문학, 허블 상수, 우주 암흑 에너지
2021.09.08
17~18 (KST)
Prof. Yeon Ui Lee
Chungbuk National University
Metamaterial Assisted Optical Nanoscopy
2021.06.16
Prof. Bonetti, Stefano
Ca' Foscari University
TBD
2021.06.09
Replaced by Video
2021.06.02
Prof. Cho, Suyeon
Ewha Womans University
TBD
2021.05.26
Prof. Go, Ara
Chonnam University
컴퓨터 시뮬레이션을 통한 전자계 연구
2021.05.12
Prof. Ha, Meesoon
Chosun University
통계물리로 이해하는 비평형 복잡계: 보편성과 다양성
(Universality and Diversity in Nonequilibrium Complex Systems)
2021.04.28
Prof. Kim, Keun-Young
GIST

중력으로 보는 양자물리

양자 물리가 주로 미시적인 세계를 묘사하는 반면, 고전 중력 이론은 거시적인 세계를 기술하며 시공간의 구조를 설명한다. 언뜻 보기에, 이 두 개의 패러다임은 설명하는 물리 현상과 적용되는 영역이 달라서 큰 관계가 없어 보인다. 하지만, 최근에 활발하게 연구되는 홀로그래픽 쌍대성 (holographic duality, gauge/gravity duality, or AdS/CFT correspondence)은, 이 두 개의 패러다임이 하나의 현상을 보는 다른 관점일 수 있다고 주장한다. 여기에서 "홀로그래픽"은 중력 이론의 시공간 차원이 양자 이론의 시공간 차원 보다 더 많기 때문에 붙여진 수식어이다. 본 강연에서는 홀로그래픽 쌍대성의 기본 아이디어를 간단히 설명한다. 그리고 그 적용의 예로서, 강상호 작용하는 응집물질물리와 양자 얽힘과 같은 양자정보 이론을 고전 중력 이론의 관점에서 어떻게 이해할 수 있는지 소개한다.

2021.04.07
Prof. Won, Eunil
Korea University
우주 탄생의 비밀을 찾아서
2021.03.31
Prof. Lee, Byoung Hoon
Ewha Womans University
Highly Oriented and Aligned Semiconducting Polymers for Flexible and Stretchable Electronics
2021.03.24
Prof. Choi, Taeyoung
Ewha Womans University
양자의 세계
2021.03.17
Prof. Ahn, Chang Rim
Ewha Womans University
섭동의 한계를 넘어서
2021.03.10
백은경 동문(93)
Korea institute of Radiological & Demical Science
방사선의학과 물리학
Please contact us if you want to join this colloquium.

Contact information:

sh_kwon@ewhain.net (new)
yugyeongje@gmail.com
yugyeongje@ewhain.net

For more information, visit the Ewha Physics Department page.