磁場におけるグラフェンのp-n交差点における量子化輸送
1Department of Physics, Center for Materials Sciences and Engineering, Massachusetts Institute of Technology, 77 Massachusetts Avenue, Cambridge, MA 02139, USA.
Science (New York, N.Y.)
|June 30, 2007
まとめ
グラフェンp-n結合は,エッジモードにより量子ホール効果を発揮する. 二極体制では粒子のモードと穴のモードが混ざり合って騒音を引き起こし,一方一極体制では無音のままである.
科学分野:
- 凝縮物質物理学 凝縮物質物理学
- マテリアルサイエンス 材料科学
- 量子力学は,量子力学という
背景:
- グラフェンは,質量のないディラクフェルミオンにより,ユニークな電子特性を示しています.
- 量子ホール効果 (QHE) は,強い磁場下にある2D電子系において観察される.
- グラフェンp-n結合は,ローカルゲーティングを使用して製造され,新しい電子行動を生み出します.
研究 の 目的:
- グラフェンp-n交差点における観測された伝導率定量化を説明するために.
- 輸送現象における量子ホールエッジモードの役割を明らかにする.
- 単極と双極の間の輸送行動の違いを理解するために.
主な方法:
- 量子ホールのエッジモード伝播に基づく理論的説明.
- p-nインタフェースでの電子と穴モードの混合の分析.
- 導電量定量化とショットノイズ特性の調査.
主要な成果:
- 観測された伝導量の定量化は,双極状態では分数,単極状態では整数である.
- 電子と穴のモードは,双極状態のp-n境界で混合する.
- 量子化されたショットノイズの高原は双極圏では観測されるが,単極圏では静音な輸送が観察される.
結論:
- グラフェンp-n結合における量子ホール現象は,エッジモードに起因する.
- グラフェンキャリアの質量のないダイラック性質は,粒子/穴の相互作用につながります.
- バイポラー状態におけるモードミックスとノイズは,この相互作用の直接的な結果である.
関連する概念動画
01:28Magnetic Fields
A moving charge or a current creates a magnetic field in the surrounding space, in addition to its electric field. The magnetic field exerts a force on any other moving charge or current that is present in the field. Like an electric field, the magnetic field is also a vector field. At any position, the direction of the magnetic field is defined as the direction in which the north pole of a compass needle points.
A magnetic field is defined by the force that a charged particle experiences...
A magnetic field is defined by the force that a charged particle experiences...
01:25Magnetic Field due to Moving Charges
A stationary charge creates and interacts with the electric field, while a moving charge creates a magnetic field.
Consider a point charge moving with a constant velocity. Like the electric field, the magnetic field at any point is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance between the source point and the field point. However, unlike the electric field, the magnetic field is always perpendicular to the plane containing the line...
Consider a point charge moving with a constant velocity. Like the electric field, the magnetic field at any point is directly proportional to the magnitude of the charge and inversely proportional to the square of the distance between the source point and the field point. However, unlike the electric field, the magnetic field is always perpendicular to the plane containing the line...
01:24Potential Due to a Magnetized Object
Magnetic dipoles in magnetic materials are aligned when placed under an external magnetic field. For paramagnets and ferromagnets, dipole alignment occurs in the direction of the magnetic field. However, the dipoles align opposite to the field in the case of diamagnets. This state of magnetic polarization due to the external field is called magnetization. Magnetization is defined as the dipole moment per unit volume. It plays a similar role to polarization in electrostatics.
The vector...
The vector...
01:28Magnetostatic Boundary Conditions
An electric field suffers a discontinuity at a surface charge. Similarly, a magnetic field is discontinuous at a surface current. The perpendicular component of a magnetic field is continuous across the interface of two magnetic mediums. In contrast, its parallel component, perpendicular to the current, is discontinuous by the amount equal to the product of the vacuum permeability and the surface current. Like the scalar potential in electrostatics, the vector potential is also continuous...
01:11P-N junction
A p-n junction is formed when p-type and n-type semiconductor materials are joined together. At the interface of the p-n junction, holes from the p-side and electrons from the n-side begin to diffuse into the opposite sides due to the concentration gradient. This diffusion of carriers leads to a region around the junction where there are no free charge carriers, known as the depletion region. The charge density within the depletion region for the n-side and p-side can be described by the...
01:31Transport Number
The transport number is the fraction of the total current carried by an ion in an electrolyte solution. It is defined as the ratio of the current carried by a specific ion to the total current flowing through the solution. The transport number, t, is central to understanding ionic mobility, which describes how fast an ion moves under the influence of an electric field. This link connects the physical behavior of ions in solution to the chemical processes that occur during electrochemical...