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RISS 인기검색어
- 검색키워드
- 저자 : Tak-Pong Woo (검색결과 4 건)
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Weak localization and universal conductance fluctuations in multi-layer graphene
Chiashain Chuang,Tak-Pong Woo,Akram M. Mahjoub,Takahiro Ouchi,Chang-Shun Hsu,Chia-Pei Chin,Nobuyuki Aoki,Li-Hung Lin,Yuichi Ochiai,Chi-Te Liang 한국물리학회 2014 Current Applied Physics Vol.14 No.1
We have performed magneto transport measurements on a multi-layer graphene device fabricated by conventional mechanical exfoliation. Suppression of weak localization (WL) as evidenced by the negative magnetoresistance (NMR) centered at zero field, and reproducible universal conductance fluctuations (UCFs) are observed. Interestingly, it is found that the phase coherence lengths calculated by fitting the observed NMR to conventional WL theory are longer than those determined from fitting the amplitudes of the UCFs to theory in the low temperature regime (T 8 K). In the high temperature regime (T > 8 K), the phase coherence lengths calculated by fitting the observed NMR to conventional WL theory are shorter than those determined from fitting the amplitudes of the UCFs to theory. Our new results therefore indicate a difference in the electron phase-breaking process between the two models of WL and UCFs in graphene.We speculate that the presence of the capping and bottom graphene layers, which leads the enhancement of disorder in-between, improves the localization condition for WL effect during carrier transportation in the low temperature regime. With increasing temperature, the localization condition for WL in multi-layer graphene becomes much weaker due to strong thermal damping. Therefore, the phase coherence lengths calculated by fitting the observed NMR to conventional WL theory are shorter than those determined from fitting the amplitudes of the UCFs to theory at high temperatures.
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Non-monotonic Magnetoresistivity in Two-dimensional Electron Systems
Yi-Ting Wang,Tak-Pong Woo,Shun-Tsung Lo,김길호,Chi-Te Liang 한국물리학회 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.65 No.10
The connection being studied is the one between the non-monotonic magnetoresistivity (MR) andthe electron-electron interaction (EEI) correction in weakly-disordered two-dimensional electronsystems (2DESs) in the ballistic region kBT/~ > 1, where kB, T, , and ~ are the Boltzmannconstant, the temperature, the scattering time, and the reduced Planck constant, respectively. Atzero magnetic field, a transition of the resistivity (T) from the insulating region d/dT < 0 tothe metallic region d/dT > 0 is observed. The MR shows a maximum, and with increasing T,the position of the MR maximum in B increases for both GaAs-based (sample A) and GaN-based(sample B) 2DESs. Our data suggest that the EEI plays an important role in such a non-monotonicMR effect and in the temperature dependence of the resistivity.
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Wang, Yi-Ting,Woo, Tak-Pong,Lo, S.-T.,Kim, Gil-Ho,Liang, Chi-Te Korean Physical Society 2014 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.64 No.10
In this report, we will discuss the nonmonotonic magnetoresistance (MR) in an AlGaN/GaN high-electron-mobility transistor (HEMT) in a perpendicular magnetic field B in the ballistic region (kBT tau/A < 1) and in the weakly-disordered limit (kFl = 159 a parts per thousand << 1), where kB, T, tau, A , k F, and l represent the Boltzmann constant, temperature, elastic scattering time, reduced Planck constant, Fermi wave vector and mean free path, respectively. The MR shows a local maximum between the weak localization (WL) and the Shubnikov-de Haas regions. In the low magnetic field regime, the quantum correction to the conductivity is proportional to T (-3/2), which is consistent with a recent theory [T. A. Sedrakyan, and M. E. Raikh, Phys. Rev. Lett. 100, 106806 (2008)]. According to our results, as the temperature is increased, the position of the MR maximum in B increases. These results cannot be explained by present theories. Moreover, in the high-magnetic-field regime, neither the magnetic and nor the temperature dependences of the observed MR is consistent with present theories. We, therefore, suggest that while some features of the observed nonmonotonic MR can be successfully explained, further experimental and theoretical studies are necessary to obtain a thorough understanding of the MR effects.
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Thermometry for Dirac Fermions in Graphene
Fan-Hung Liu,Chang-Shun Hsu,Shun-Tsung Lo,Chiashain Chuang,Lung-I Huang,Tak-Pong Woo,Chi-Te Liang,Y. Fukuyama,Y. Yang,R. E. Elmquist,Pengjie Wang,Xi Lin 한국물리학회 2015 THE JOURNAL OF THE KOREAN PHYSICAL SOCIETY Vol.66 No.1
We use both the zero-magnetic-field resistivity and the phase coherence time determined by weaklocalization as independent thermometers for Dirac fermions (DF) in multilayer graphene. In thehigh current (I) region, there exists a simple power law TDF / I0.5, where TDF is the effective Diracfermion temperature for epitaxial graphene on SiC. In contrast, TDF / I1 in exfoliated multilayergraphene. We discuss possible reasons for the different power laws observed in these multilayergraphene systems. Our experimental results on DF-phonon scattering may find applications ingraphene-based nanoelectronics.
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