柱形量子点中弱耦合磁极化子的性质

应用线性组合算符方法和幺正变换方法,研究在抛物势作用下的柱形量子点中磁极化子的性质。对ZnS量子点的数值计算表明,量子点中磁极化子的基态能量随特征频率、回旋共振频率的增大而增加,这是由于特征频率增加时振动能量、回旋共振频率增加时外磁场中的附加能量增加所致。当特征频率(或回旋共振频率)增加到某一值时,磁极化子能量由负变为正。基态能量随柱高的减小而增加,且柱高越小,增加越快;当柱高减小到某一值时,磁极化子能量也由负变为正。总之,柱形量子点中的磁极化子,其基态能量与量子点的尺度、外磁场、特征频率等有关。

Properties of Weak-Coupling Magnetopolaron in Cylinderical Quantum Dot

With the development of molecular beam epitaxy (MBE) technology and metal organic chemical vapor deposition (MOCVD) technology, there has been great interest in investigating quantum dot both in material science and condensed state physics field. Due to size of quantum dot was small, they had a series of new and serious character, for example, quantum size effect, quantum coherent effect, quantum tunnel effect, coulomb resistance effect and surface effect, etc., these had brought infinite chance and hope on development and use of new materials. Especially, electron in quantum dot was subject to a strong three-dimension (3D) confinement, so that quantum effect was quite different from those of the bulk materials, these would brought about great society benefit and economic benefit. So many scientists has been investigating properties of quantum dots. Zhu J L, et al. studied the properties of spherical quantum dot by using a few bodies method, results indicated that binding energy of donor state had depended on shape, dimension and confined potential of the quantum dots. Charrour R, et al. studied the ground state binding energy of hydrogenic impurity in cylindrical quantum dot that subjected to external strong magnetic field by using the variational procedure and considering an infinite confined potential on all surface of the system. They found that the impurity binding energy depended strongly on the impurity position, magnetic field strength and the dot size(radius and height). Zhou H Y and Gu Shiwei had studied the properties of strong-coupling magnetopolaron in a disk-shape quantum dot, they pointed that the ground state energy and the excited state energy depended on resonance frequency and confined strength. The properties of magnetopolaron with electron-LO-phonon weak-coupling in cylindrical quantum dot, which was in parabolic potential, were investigated by using the linear combination operator and unitary transformation methods. Numerical calculations for ZnS quantum dot indicated that the ground state energy increased with increa sing characteristic frequency and cyclotron-resonance frequency,since vibration energy increased with increasing characteristic frequency and additional energy in external magnetic field increased with increasing cyclotron-resonance frequency, the energy of magnetiopolaron changed position from negative when characteristic frequency(or cyclotron-resonance frequency) increased to the value,for example, which was 0.27ω_LO for the case of cylinder height L =20 nm and cyclotron resonance frequency ω_c=0.5ω_LO (or ω_c was 0.5ω_LO for the case of L=20 nm and characteristic frequency ω₀=0.27ω_LO ). The ground state energy increased with increasing cylinder height, the smaller cylinder height was, the faster it increased, the energy of magnetopolaron also changed positive from negative when cylinder height decreased to 33.1 nm for the case of ω_c=ω₀=0.5ω_LO. In short, ground state energy of bounding magnetopolaron in cylindrical quantum dot had something to do with size of quantum dot, external magnetic field and characteristic frequency.