共查询到20条相似文献,搜索用时 125 毫秒
1.
2.
3.
4.
《低温物理学报》2016,(5)
晶体的物理性质可以通过晶体掺杂的方式来改变.因此,在这工作中,我们研究了Br掺杂效应对(CH_3)_2NH_2Cu(Cl_(1-x)Br_x)_3(0≤x≤1)晶体的结构,物理性质及比热的影响.研究表明,晶体结构几乎不受Br掺杂影响,而温度T2K的磁性质,其随掺杂浓度的变化而变化.掺杂浓度从x=0到x=1变化过程中,磁相互作用从顺磁态变为铁磁态.这现象可理解为随着掺杂浓度增大,最近邻磁性离子间相互作用发生改变,导致x=0晶体的磁结构中反铁磁二聚化解体.不同磁场下x=0和x=1掺杂的晶体比热研究,x=1晶体的磁比热在温度2-4.5K区域呈现出一个随磁场变化的"肩",表明存在于x=0晶体中的自发反铁磁有序相和磁场诱导有序相被抑制.综上所述,磁性质和比热特征均表明掺杂能有效改变物理性质:x=0晶体的磁结构中反铁磁二聚化解体,x=1掺杂的磁结构演变成铁磁二聚化的反铁磁链. 相似文献
5.
一维受限反铁磁光子晶体的性质 总被引:4,自引:0,他引:4
采用传输矩阵法计算了一维受限反铁磁光子晶体的带结构和透射比.研究结果表明:除来源于结构周期性的光子带隙外,体系还存在一种频率带隙,与反铁磁材料的共振性质以及受限尺寸有关.适当调节反铁磁各向异性轴的方向和受限尺寸,在反铁磁共振频率处可以出现比大块反铁磁材料的带隙宽约15倍的频率带隙.一定条件下,在大块反铁磁材料带隙的频率区间上,一些电磁波模式是可以在受限光子晶体中传播的.最后分析了几种典型的透射谱,与带结构吻合. 相似文献
6.
基于密度泛函理论(DFT),使用局域密度近似(LDA)研究了Heusler合金Cu1-xFex MnSb的电子结构和反铁磁-铁磁相变.研究发现,两种磁状态下的合金晶格常数随掺杂浓度x变化很好地满足Vegard定理.当x0.5时,铁磁态合金的总磁矩很好地符合SP规律,然而当x0.5时,却发生了明显的偏离.由于整个体系存在RKKY和超交换磁耦合的竞争,因而在x=0.25时,我们观察到了独特的反铁磁—铁磁相变.进一步的态密度分析发现,Cu的掺杂浓度可以有效调整铁磁态合金的费米面位置,并且反铁磁态合金由于不同自旋方向的Mn原子的分波态密度相互补偿,总态密度形成了几乎完全对称的自旋向上带和自旋向下带. 相似文献
7.
利用光学传输矩阵方法,模拟计算了由铁磁材料组成的一维光子晶体的光学传输特性.研究了能带结构随介质层厚度h(O ≤h≤0.5λ0 λ0=1.2×10-6m)变化的规律,并与相同周期结构的普通光子晶体的传输特性进行了比较.结果表明,当O.15λ0<h<0.165λ0时,铁磁光子晶体的带隙宽度略小于普通光子晶体的带隙宽度;在h取其他值时铁磁光子晶体的带隙宽度远远大于普通光子晶体的带隙宽度,并且在h=0.25λ0时存在最大值.这种结构的光子晶体通过掺杂有望在多通窄带滤波技术中得到广泛的应用. 相似文献
8.
利用电化学结晶的方法制备了高质量的(BEDT-TTF)[FeBr4]单晶, 通过四圆单晶衍射确定了其晶体结构为三斜晶系. 在高温区, 晶体电阻率与电子的热激发效率以及载流子受电离杂质散射的强弱有关. 在低温区, 晶体的导电性只依赖体内杂质缺陷等的电离. 由于电子受到Lorentz力的作用增加了与晶格的碰撞次数, 晶体的磁阻率表现为正值. 晶体的磁性主要由三价铁离子决定, 晶体中三价铁离子之间不具有铁磁耦合或反铁磁耦合. 电子顺磁共振谱中同时发现πup 电子和d电子的共振信号, 温度降低可使πup 电子和d电子的耦合作用增强, 晶体沿着不同轴旋转, 其共振信号随旋转角度的变化存在着巨大的差异. 相似文献
9.
10.
使用基于自旋局域密度泛函理论的第一性原理方法对3d过渡金属(TM=V,Cr,Mn,Fe,Co和Ni)掺杂的Ⅲ-Ⅴ族半导体(GaAs和GaP)的电磁性质进行了计算.结果发现:用V,Cr和Mn掺杂时体系将出现铁磁状态,而Fe掺杂时将出现反铁磁状态,Co和Ni掺杂时,其磁性则不稳定.其中,Cr掺杂的GaAs和GaP将可能是具有较高居里温度的稀磁半导体(DMS).在这些DMS系统中,V离子的磁矩大于理论期待值,Fe,Co和Ni离子的磁矩小于理论期待值,Cr和Mn离子的磁矩与期待值的差距取决于晶体的对称性以及磁性离子的能带分布.此外,使用Si和Mn共同对Ⅲ-Ⅴ族半导体进行掺杂,将有利于DMS表现为铁磁状态,并可以使体系的TC进一步提高.
关键词:
稀磁半导体
过渡金属
掺杂
共掺杂 相似文献
11.
Using the basic ingredient of supersymmetry, a simple alternative approach is developed to perturbation theory in one-dimensional non-relativistic quantum mechanics. The formulae for the energy shifts and wavefunctions do not involve tedious calculations which appear in the available perturbation theories. The model applicable in the same form to both the ground state and excited bound states, unlike the recently introduced supersymmetric perturbation technique which, together with other approaches based on logarithmic perturbation theory, are involved within the more general framework of the present formalism. 相似文献
12.
《中国科学:物理学 力学 天文学(英文版)》2020,(11)
We investigate the implication of trans-Planckian censorship conjecture(TCC) for the initial state of primordial perturbations. It is possible to set the state of perturbation modes in the infinite past as the Minkowski vacuum, only if the pre-inflationary era is past-complete. We calculate the evolution of the perturbation modes in such a pre-inflationary era and show that at the beginning of inflation the perturbation modes with wavelengths much shorter than the Hubble scale(but still larger than the Planck length scale) will behave as they are in the Bunch-Davis state. Therefore, a past-complete pre-inflationary evolution may automatically prepare the initial state required for the inflationary perturbations at the CMB window while obeying the TCC. 相似文献
13.
Analysis of a dissipative two-state system at zero temperature shows that the model Hamiltonian may be exactly reduced to a modified quantum sine-Gordon model, which describes the effective interactions between the low-frequency phonons under coupling with a tunneling system. Directly considering the infrared divergence encountered in the conventional perturbation treatment, we have developed a new perturbation approach for the effective Hamiltonian, and derived the exact critical conditions for the localization transition. In the critical regime, a gap will be opened near zero momentum in the elementary excitation spectrum of the low-frequency phonons, and the corresponding ground state wave function is found to be a pairing quasi-particle state, analogous to the BCS superconducting state. 相似文献
14.
Density perturbations are considered during the radiation-dominated and the dust-dominated periods of the expanding universe. The perturbations are taken to have spherical symmetry and the investigation is carried out in the de Donder gauge. In order to guarantee the energy-momentum conservation of the perturbation in the de Donder gauge a compatibility condition is obtained. Equations for the propagation of a spherically symmetric perturbation in linear approximation on a FRW cosmological background are presented. It turns out that the evolutiontendency of the formation is mainly predicted by the state of the cosmic background. A radiation-dominated universe does not stimulate growth processes; the perturbation will be in a frozen state or it will diffuse. It is found that the dust-dominated universe stimulates the perturbation mass to grow. The rate of this cosmic affected growing process is proportional toR
–1 (R being the scale factor of the universe), so that it seems that almost all galaxies were formed at the beginning of the present dust-dominated era. 相似文献
15.
Variational-integral perturbation corrections of some lower excited states for hydrogen atoms in magnetic fields 下载免费PDF全文
A variational-integral perturbation method(VIPM) is established by combining the variational perturbation with the integral perturbation.The first-order corrected wave functions are constructed,and the second-order energy corrections for the ground state and several lower excited states are calculated by applying the VIPM to the hydrogen atom in a strong uniform magnetic field.Our calculations demonstrated that the energy calculated by the VIPM only shows a negative value,which indicates that the VIPM method is more accurate than the other methods.Our study indicated that the VIPM can not only increase the accuracy of the results but also keep the convergence of the wave functions. 相似文献
16.
We study the stability of steady state solutions of a resonantly tuned bidirectional homogeneously broadened ring laser retaining the complete longitudinal spatial dependence. We prove that in two limits, the stable steady states are only weakly stable since the relaxation rates are very large. This implies a high sensitivity to any kind of perturbation which will easily induce a transition from one direction of propagation to the other one. We also analyze a popular approximation which uses a truncated harmonic expansion and the adiabatic elimination of the polarization. When the adiabatic elimination is justified, we show that the harmonic truncation does not further limit the range of applicability of the stability analysis. 相似文献
17.
18.
We discuss the evolution of the state and the average energy of the Fermi Ulam model in the case of periodic perturbation. By a perturbation technique, the time-dependent Sehr6dinger equation is solved and it is found that the particle will continuously absorb or radiate energy Jf the frequency of the oscillating wall meets the resonance condition. Usually, these two states cannot exist together at a certain frequency. However, there is an exception if the frequency is at some special values. We find these values and reveal that the energy for transmission has the minimum equivalent unit, which is in the form of a harmonic oscillator. 相似文献
19.
本文证明,Cioslowski所引入的一个全新的量子力学计算方案,非简并基态最陡下降微扰理论,通过按对称性选择合适的零级试探波函数后,可以处理简并基态的微扰分裂问题由于最陡下降微扰理论既避免了通常的其他微扰理论需要对各个基矢量无限求和的或求解一组微分方程的缺陷,又具有逐步迭代改善计算结果的优点,本文引进的计算方案可望在原子分子及其他多粒子体系能级的微扰分裂计算中得到广泛应用。
关键词: 相似文献
20.
InAs量子环中类氢杂质能级 总被引:1,自引:0,他引:1
在有效质量近似下,利用微扰法研究了InAs量子环内类氢杂质基态及低激发态的能级分布。受限势采用抛物形势,在二维平面极坐标下,用薛定谔方程的精确解析解进行计算。数值计算结果显示,电子能级敏感地依赖于量子环半径,能级存在极小值,这是由于限制势采用抛物势的结果。如果减小环的半径,可以增加能级间距。第一激发态类氢杂质能级的简并没有消除,n≥2时简并的能级发生分裂并且间距随半径的增大而增大。电子能级间距还敏感地依赖于角频率并随角频率的增大而增大。第一激发态的简并没有消除,第二激发态的简并被部分地消除。在计算InAs量子环中类氢杂质的基态和低激发态的能级时,角频率改变的影响也是很深刻的。文章结果对研究量子环的光跃迁及光谱结构有重要指导意义。 相似文献