Fano resonance in electronic transport induced by the magnetic confinement in a graphene nanoribbon

명노준,임국형,Kyungchul Seo 한국물리학회 2013 Current Applied Physics Vol.13 No.7

Based on the Floquet scattering theory, a model of graphene-based electronic device is presented, in which electrical transport is controlled by adjusting Dirac fermions energy near resonance conditions. The presence of an oscillating field leads to the Fano resonance in transport through a magnetic structure in an armchair graphene nanoribbon (AGNR). The Fano resonance originates from bound states of the magnetic confinement, according to subband indices in the AGNR. The ballistic conductance is markedly affected by the Fano resonance due to the quasi-one-dimensional nature of AGNRs. The results may help realizing graphene electronics with the resonant characteristics in the conductance.

Gate-tunable valley-filter based on suspended graphene with double magnetic barrier structures

명노준,임국형 한국물리학회 2014 Current Applied Physics Vol.14 No.11

We theoretically investigate the effects of strain-induced pseudomagnetic fields on the transmission probability and the ballistic conductance for Dirac fermion transport in suspended graphene. We show that resonant tunneling through double magnetic barriers can be tuned by strain in the suspended region. The valley-resolved transmission peaks are apparently distinguishable owing to the sharpness of the resonant tunneling. With the specific strain, the resonant tunneling is completely suppressed for Dirac fermions occupying the one valley, but the resonant tunneling exists for the other valley. The valley-filtering effect is expected to be measurable by strain engineering. The proposed system can be used to fabricate a graphene valley filter with the large valley polarization almost 100%.

Helical states around a mass-inverted quantum dot in graphene

명노준 한국물리학회 2021 Current Applied Physics Vol.23 No.-

Topologically protected helical states at a mass-inverted quantum dot in graphene are studied by analyzing both tight-binding and kernel polynomial method calculations. The mass-inverted quantum dot is introduced by considering a heterojunction between two different mass domains, which is similar to the domain wall in bilayer graphene. The numerical results show emergent metallic channels across the mass gap when the signs of the mass terms are opposite. The eigenstates of the metallic channels are revealed to be doubly degenerate—each state propagates along opposite directions, maintaining the time-reversal symmetry of graphene. The robustness of the metallic channels is further examined, concluding with the fact that helical states are secured unless atomic vacancies form near the domain wall. Such helical states circulating along the topological defects may pave a novel route to engineering topological states based on graphene.

Spin-filtering Effect in Graphene with Double Magnetic Barrier Structures

명노준,임국형 한국물리학회 2011 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.59 No.3

We investigate spin transport in graphene with a particular profile of magnetic vector potential, the double magnetic barrier structure. The results are characterized by sharp resonant tunneling peaks in the transmission. These peaks could be spin-split under certain conditions, resulting in considerable spin-polarization in the conductance. By applying electrostatic modulation, in addition to the double barrier structures, we could change the sign of the spin polarization and observe tunable spin transport.

적층수에 따른 GFRP 피막 Al 평활재의 저주기 피로수명 평가

명노준,서지혜,이은균,최낙삼 한국복합재료학회 2018 Composites research Vol.31 No.6

Fiber metal hybrid laminate (FML) can be used as an economic material with superior mechanical properties and light weight than conventional metal by bonding of metal and FRP. However, there are disadvantages that it is difficult to predict fracture behavior because of the large difference in properties depending on the type of fiber and lamination conditions. In this paper, we study the failure behavior of hybrid materials with laminated glass fiber reinforced plastics (GFRP, GEP118, woven type) in Al6061-T6 alloy. The Al alloys were coated with GFRP 1, 3, and 5 layers, and fracture behavior was analyzed by using a static test and a low cycle fatigue test. In the low cycle fatigue test, strain - life analysis and the total strain energy density method were used to analyze and predict the fatigue life. The Al alloy did not have tensile properties strengthening effect due to the GFRP coating. The fatigue hysteresis geometry followed the behavior of the Al alloy, the base material, regardless of the GFRP coating and number of coatings. As a result of the low cycle fatigue test, the fatigue strength was increased by the coating of GFRP, but it did not increase proportionally with the number of GFRP layers. 섬유 금속 적층판(Fiber metal hybrid laminate, FML)은 금속재료와 FRP의 접합으로 기존의 금속 소재가 가지지 못했던 뛰어난 물성과 가벼운 무게로 경제적인 구조용 재료로 사용된다. 그러나 섬유의 형태와 종류, 적층조건에 따라 물성의 차이가 크며, 파괴거동을 예측하기 어렵다는 단점이 있다. 본 논문에서는 Al6061-T6 합금에직조형태의 유리섬유 플라스틱(GFRP, GEP118)을 적층피막한 복합재의 파손거동에 대해 연구한다. Al합금에 GFRP 1, 3, 5 겹을 피막한 3가지 조건으로 성형하고, 피막의 적층수를 변수로 정적시험과 저주기 피로시험을 병행하여파손거동을 분석하였다. 저주기 피로시험에서는 변형률-수명 해석, 전변형률 에너지밀도법을 사용하여 분석하고, 피로수명을 예측하여 하이브리드 재료에 대한 수명예측성을 분석하였다. 인장해석 결과, GFRP 피막으로 인한 강화효과는 없었고, 피로시험시 나타나는 히스테리시스 형상은 GFRP피막 유무와 피막 수에 상관없이 모재인 Al합금의 거동을 따랐다. 저주기 피로시험 결과 GFRP의 피막으로 피로강도가 증가하였지만, GFRP의 두께에 따라 비례하여 증가하지는 않았다.

Demonstration of Magnetic Confinement in Graphene with Fano-type Resonances

명노준,서경철,임국형 한국물리학회 2013 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.62 No.2

We demonstrate the magnetic confinement in graphene by investigating the Fano-type resonant features in the transmission spectra. The Fano-type resonance occurs due to the interference between extended states and magnetically-bound states as a result of the interaction of Dirac fermions with the oscillating field. We also find another type of resonance that results from the quasi-bound states induced by the oscillating field. In contrast to the magnetically-bound states, the quasibound states generally have complex eigenenergies whose imaginary parts are associated with finite lifetimes. The results may inspire experimental research on magnetic confinement in graphene.

그래핀에서 자기장에 의한 디랙점에서의 고유함수 변조

명노준,임국형 한국물리학회 2019 새물리 Vol.69 No.11

우리는 그래핀에서 자기장에 의한 디랙점에서의 고유함수 변조를 연구하였다. 디랙점은 그래핀의 육각형모양의 브릴루앙 영역에 있는 꼭지점에 해당하는데 도핑이 되지 않은 그래핀에서는 화학퍼텐셜이 정확하게디랙점을 지난다. 디랙점에서 펼쳐지는 원추형의 에너지 스팩트럼은 선형적 분산을 보여주며 상태 밀도는에너지(E)에 비례한다. 따라서 E = 0 인 디랙점에서는 고유상태가 존재하지 않는다. 하지만 자기장을걸어주면 그래핀의 상태 밀도가 변하게 되어 디랙점에도 국소화된 상태가 존재할 수 있게 된다. 비정상적인정수 양자홀 효과는 대표적인 예이다. 이에 더하여 우리는 그래핀 위에 자기 양자점(특정 반경의 원 안에는B = 0이지만 그 밖에는 일정한 B)이 형성된 경우와 자기 반양자점(특정 반경의 원 밖에는 B = 0 이지만 그 안에는 일정한 B) 이 형성된 경우를 조사하였다. 두 경우 모두 디랙점에서 특징적인 국소화 상태가존재함을 확인하였고 분석하였다. 우리의 결과는 그래핀 소자 기술에 유용하게 응용될 것이다. We investigate the modulation of eigenstates at the Dirac point by using a magnetic field in graphene. In neutral graphene, the chemical potential crosses exactly the Dirac points, which are the corners of graphene’s hexagonal Brillouin zone. The conical energy spectrum with its vertex on Dirac point reflects the linear dispersion, and the density of states is found to be proportional to the energy, g(E) E. Thus, no eigenstates where E = 0 are found at the Dirac points. However, the introduction of a magnetic field (B) modifies g(E) and allows localized states to exist at the Dirac points. The anomalous integer quantum Hall effect is a typical example. We also considered two more cases; a magnetic quantum dot (nonzero B outside the circle; otherwise, B = 0) and a magnetic anti-quantum dot (nonzero B inside the circle; otherwise, B = 0) formed in graphene. The characteristic localized states at the Dirac points (E = 0) are found and analyzed for both cases. Our results may be usefully applied in graphene device technology.

그래핀에 형성된 자기 양자점의 에너지 스펙트럼

명노준,임국형 한국물리학회 2017 새물리 Vol.67 No.10

우리는 그래핀 위에 불균일 자기장을 인가하여 형성된 자기 양자점의 고유에너지에 대해 연구를 수행하였다. 본 연구의 동기는 그래핀 위에 정전기 퍼텐셜을 이용하여 양자구조를 만드는데 존재하는 어려움들을 자기 퍼텐셜을 이용하면 극복할 수 있기 때문이다. 양자점에 강하게 국소 된 상태들이 양자홀 영역에서 발견되는데 이들은 양자점의 경계를 따라 시계 방향 또는 반시계 방향으로 도는 자기 끝머리 상태들로 이해할 수 있다. 고유 에너지 스펙트럼은 자기 양자점의 비균일한 자기장으로 말미암아 없어진 자기 선속 양자수에 크게 의존한다. 이러한 국소 상태들은 실험적으로 증명될 수 있는데 작은 그래핀 도체 위의 중앙에 자기 양자점을 형성하고 도체의 양 끝을 흐르는 두 단자 전기전도율을 측정하면 이들 국소 상태들을 통한 공명 후방산란 효과가 나타나게 된다. We investigate the eigen energies of a magnetic quantum dot formed in graphene by using the inhomogeneous distributions of magnetic fields. The motivation of our study is to overcome the existing difficulties in the formation of quantum structures in graphene via electrostatic confinements. Strongly localized states on the magnetic quantum dot are observed in the quantum Hall region and can be understood by using magnetic edge states circulating either clockwise or counterclockwise along the boundary of the dot. The eigen energy spectra are shown to depend critically on the number of missing flux quanta in the magnetic quantum dot. The existence of localized magnetic edge states can be proven experimentally by measuring the two-terminal conductance of a small graphene conductor with a magnetic quantum dot formed in its center, which reflects resonant backscattering via the magnetic edge states.

초음파 피로시험시 시험편의 유한요소 동적 해석

명노준(No-Jun Myeong),최낙삼(Nak-Sam Choi),권현화(Hena Kwon) 대한기계학회 2014 大韓機械學會論文集A Vol.38 No.7

본 논문에서는 초고주기피로영역의 가속시험 방법인 초음파 피로시험에 대해 20 kHz 근처에서 시험편 게이지부의 동적거동을 유한요소해석으로 검토하였다. 실제 실험에서 시험편에 작용하는 응력은 시험편의 형상과 변위를 통해 식으로 계산되는데 여기서 가정하는 시험편의 형상과 실제 시험편의 형상에 차이가 발생한다. 실험으로 구해진 응력과 유한요소 동적 해석의 결과를 비교하고 형상차이에 따른 응력분포를 확인하였다. 또한, 이론적으로 생각하는 초음파 피로시험기의 동적 거동을 가시적으로 확인하여 초음파 피로시험의 정확성을 확보하였다. An accelerated ultrasonic fatigue test (UFT) was used for analyzing very high cycle fatigue (VHCF, Nf > 107) behaviors of a specimen with a test resonance of 20 kHz. Using the finite element method (FEM), the dynamic behaviors of the specimen was studied by calculating the stresses along its gauge portion, with displacement. The shape of gauge portion profile was assumed to be a hyperbolic according to the stress equation of the UFT. However, as the specimen used in the test had a circular arc profile, the FEM was used for studying the local stresses for two cases of the gauge profile. The results were compared with those obtain from the stress equation of the UFT. The dynamic behavior of the gauge portion could be understood for further comparison with the actual results.

회주철(GC300)의 주조방법에 따른 인장강도 분석 및 확률론적 피로수

명노준(NohJun Myung),성용현(Yong Hyeon Sung),최낙삼(Nak-Sam Choi) 대한기계학회 2017 대한기계학회 춘추학술대회 Vol.2017 No.4