坂本 昇一

We present here the first principle calculations of the electrical properties of in-plate heterojunctions of armchair graphene nanoribbon/h-BN(AGNR/h-BN)s. The calculations are carried out using SIESTA package, which is comprised of numerical codes of the density functional theory(DFT) and the non-equilibrium Green's function(NEGF). Especially, adopting the conductive (3n-1)-family of AGNR((3n-1)-AGNR) makes the lead parts on both side of the model metallic. Two transverse arrays of h-BN, which is a wide-gap semiconductor, are embedded in the middle of (3n-1)-AGNR and act as a double barrier system. The quantum double barrier tunneling is found in the transmission functions(TF) and I-V characteristics of 8, 11, 14-AGNR/h-BN. The TF shows significantly spiky peaks in the neighborhood of the Fermi energy, and consequently, it results in step-sise I-V characteristics. Simple one-dimensional Dirac equation model for the double barrier system is also proposed to analyze numerical results. Our model reproduces most of the peaks of the transmission functions nearby the Fermi energy, as a result of quantum tunneling.

This study analyzed the scar-like localization in the time-average of a time-evolving wavepacket on a desymmetrized stadium billiard. When a wavepacket is launched along the orbits, it emerges on classical unstable periodic orbits as a scar in stationary states. This localization along the periodic orbit is clarified through the semiclassical approximation. It essentially originates from the same mechanism of a scar in stationary states: piling up of the contribution from the classical actions of multiply repeated passes on a primitive periodic orbit. To achieve this, several states are required in the energy range determined by the initial wavepacket.

We present the first principle calculations of the electrical properties of graphene sheet/h-BN heterojunction (GS/h-BN) and 11 -armchair graphene nanoribbon/h-BN heterojunction (11 -AGNR/h-BN), which are carried out using the density functional theory (DFT) method and the non-equilibrium Green's function (NFGF) technique. Since 11 -AGNR belongs to the conductive (3n-l )-family of AGNR, both are metallic nanomaterials with two transverse arrays of li-BN, which is a wide-gap semi-conductor. The two h-BN arrays act as double barriers. The transmission functions (TF) and I-V characteristics of GS/h-BN and 11 -AGNR/h-BN are calculated by DFT and NFGF, and they show that quantum double barrier tunneling occurs. The TF becomes very spiky in both materials, and it leads to step-wise I-V characteristics rather than negative resistance, which is the typical behavior of double barriers in semiconductors. The results of our first principle calculations are also compared with ID Dirac equation model for the double barrier system. The model explains most of the peaks of the transmission functions nearby the Fermi energy quite well. They are due to quantum tunneling.

<p>グラフェンはシリコンに代わる次世代デバイスの材料として期待されている。本研究では、グラフェンを2次元電子デバイスに応用するために、グラフェン/h-BNヘテロ接合における電子特性を密度汎関数法および非平衡グリーン関数法に基づいて解析する。特にジグザグ型グラフェンナノリボンへの接合では、エッジ状態への影響や自発的スピン分極の発現の有無に注目し、h-BNがグラフェンに及ぼす効果を検証する。</p>