This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high trans...This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the ＇hard gap＇ energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained.展开更多
A series of high quality single crystalline epitaxial Zn 0.95 Co 0.05 O thin films is prepared by molecular beam epitaxy.Superparamagnetism and ferromagnetism are observed when the donor density is manipulated in a ra...A series of high quality single crystalline epitaxial Zn 0.95 Co 0.05 O thin films is prepared by molecular beam epitaxy.Superparamagnetism and ferromagnetism are observed when the donor density is manipulated in a range of 10 18 cm 3-10 20 cm 3 by changing the oxygen partial pressure during film growth.The conduction shows variable range hopping at low temperature and thermal activation conduction at high temperature.The ferromagnetism can be maintained up to room temperature.However,the anomalous Hall effect is observed only at low temperature and disappears above 160 K.This phenomenon can be attributed to the local ferromagnetism and the decreased optimal hopping distance at high temperatures.展开更多
On the insulating side of the metal-insulator transition (MIT), the study of the effect of low Temperatures T on the electrical transport in amorphous silicon-nickel alloys a-Si1-yNiy:H exhibits that the electrical co...On the insulating side of the metal-insulator transition (MIT), the study of the effect of low Temperatures T on the electrical transport in amorphous silicon-nickel alloys a-Si1-yNiy:H exhibits that the electrical conductivity follows, at the beginning, the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T-1/2. This behaviour showed that long range electron-electron interaction reduces the Density Of State of carriers (DOS) at the Fermi level and creates the Coulomb gap (CG). For T higher than a critical value of temperature TC, we obtained the Mott Variable Range Hopping regime with T-1/4, indicating that the DOS becomes almost constant in the vicinity of the Fermi level. The critical temperature TC decreases with nickel content in the alloys.展开更多
We demonstrate transitions of hopping behaviors for delocalized electrons through the discrete dopant-induced quantum dots in n-doped silicon junctionless nanowire transistors by the temperature-dependent conductance ...We demonstrate transitions of hopping behaviors for delocalized electrons through the discrete dopant-induced quantum dots in n-doped silicon junctionless nanowire transistors by the temperature-dependent conductance characteristics.There are two obvious transition platforms within the critical temperature regimes for the experimental conductance data,which are extracted from the unified transfer characteristics for different temperatures at the gate voltage positions of the initial transconductance gm peak in Vg1 and valley in Vg2. The crossover temperatures of the electron hopping behaviors are analytically determined by the temperature-dependent conductance at the gate voltages Vg1 and Vg2. This finding provides essential evidence for the hopping electron behaviors under the influence of thermal activation and long-range Coulomb interaction.展开更多
In this paper, we discuss low-temperature hopping-conductivity behavior in the insulating phase, in the absence of a magnetic field. We conduct a theoretical study of the crossover from hopping to activated transport ...In this paper, we discuss low-temperature hopping-conductivity behavior in the insulating phase, in the absence of a magnetic field. We conduct a theoretical study of the crossover from hopping to activated transport in a GaAs two-dimensional hole system at low temperatures, finding that a crossover takes place from the Efros-Shklovskii variable-range hopping(VRH)regime to an activated regime in this system. This conductivity behavior in p-GaAs quantum wells is qualitatively consistent with the laws laid down in theories of localized electron interactions. Given sufficiently strong interactions, the holes in the localized states are able to hop collectively.展开更多
We reanalyzed experimental data already published in Friedman J R, Zhang Y, Dai P, et al. Phys Rev B, 1996, 53（15）： 9528. Variable range hopping （VRH） conduction in the insulating three-dimensional n-CdSe samples...We reanalyzed experimental data already published in Friedman J R, Zhang Y, Dai P, et al. Phys Rev B, 1996, 53（15）： 9528. Variable range hopping （VRH） conduction in the insulating three-dimensional n-CdSe samples has been studied over the entire temperature range from 0.03 to 1 K. In the absence of a magnetic field, the low temperature conductivity a of the three samples （A, B and C） obeys the Mott VRH conduction with an appropriate temperature dependence in the prefactor （a = σ0 exp [- （T0/T）]^p with p ≈ 0.25）. This behavior can be explained by a VRH model where the transport occurs by hopping between localized states in the vicinity of the Fermi level, EF, without creation of the Coulomb gap （CG）. On the contrary, no Efros-Shklovskii VRH is observed, suggesting that the density is constant in the vicinity of the EF.展开更多
通过电阻率-温度(temperature dependence of resistivity,ρ-T)曲线、磁化强度-温度(temperature depen-dence of magnetization,M-T)曲线、ESR谱线的测量,研究了La0.45Ca0.55MnO3样品的电磁特性。结果表明,样品在整个测量温区呈现绝...通过电阻率-温度(temperature dependence of resistivity,ρ-T)曲线、磁化强度-温度(temperature depen-dence of magnetization,M-T)曲线、ESR谱线的测量,研究了La0.45Ca0.55MnO3样品的电磁特性。结果表明,样品在整个测量温区呈现绝缘体行为,输运机制满足可变程跃迁模型。样品存在电荷有序(charge ordering,CO)相,相变温度TCO≈240K,并随温度降低发生顺磁(paramagnetism,PM)→电荷有序(CO)→反铁磁(antiferromagnetism,AFM)变化。值得注意的是,由于样品低温下存在多种复杂的磁相互作用,在40K发生自旋玻璃转变,表现为再入型自旋玻璃行为。展开更多
为了有效地解决多跳频信号的盲源分离问题,提出了一种变步长的EASI(Equivariant Adaptive Separation via Independence)盲源分离算法。该算法在传统EASI算法的等变化性基础上,用性能指标(串音误差)作为准则,通过改变函数的取值范围及形...为了有效地解决多跳频信号的盲源分离问题,提出了一种变步长的EASI(Equivariant Adaptive Separation via Independence)盲源分离算法。该算法在传统EASI算法的等变化性基础上,用性能指标(串音误差)作为准则,通过改变函数的取值范围及形状,自适应更新步长,使其在一个固定小的范围内,达到算法收敛速度和稳定性能的一个较理想的平衡点,改善了当步长固定时存在的缺陷。经过实验仿真,证明该算法对步长有很好的调整能力,性能稳定且收敛速度较快,能很好地将多个跳频信号进行分离,较传统的EASI算法有更高的适用性。展开更多
提出一种单相电源供电时适用于异步电机传动的单相–三相变换器。由于仅采用7个晶闸管和1个移相电容,该变换装置具有造价低、结构简单的特点。分析该变换器的工作原理及开关过程,并提出一种基于开环变压变频(variable voltage variable ...提出一种单相电源供电时适用于异步电机传动的单相–三相变换器。由于仅采用7个晶闸管和1个移相电容,该变换装置具有造价低、结构简单的特点。分析该变换器的工作原理及开关过程,并提出一种基于开环变压变频(variable voltage variable frequency,VVVF)和变压恒频(variable voltage constant frequency,VVCF)控制的单相–三相离散跳频控制策略,用于电机的起动和稳态运行控制,一方面保证了电机在低频阶段足够大的起动力矩,另一方面可使电机稳步起动到额定转速。仿真和实验结果表明了该控制策略的有效性以及系统方案的可行性。展开更多
基金Project supported by the National Basic Research Program of China (Grant Nos. 2007CB924903 and 2009CB929202)the National Natural Science Foundation of China (Grant No. 10974120)
文摘This paper proposes a universal spin-dependent variable range hopping theoretical model to describe various experimental transport phenomena observed in wide-band-gap oxide ferromagnetic semiconductors with high transition metal concentration. The contributions of the ＇hard gap＇ energy, Coulomb interaction, correlation energy, and exchange interaction to the electrical transport are considered in the universal variable range hopping theoretical model. By fitting the temperature and magnetic field dependence of the experimental sheet resistance to the theoretical model, the spin polarization ratio of electrical carriers near the Fermi level and interactions between electrical carriers can be obtained.
基金Project supported by the State Key Project of Fundamental Research of China (Grant No. 2009CB929202)the National Natural Science Foundation of China (Grant Nos. 10834001 and 51125004)
文摘A series of high quality single crystalline epitaxial Zn 0.95 Co 0.05 O thin films is prepared by molecular beam epitaxy.Superparamagnetism and ferromagnetism are observed when the donor density is manipulated in a range of 10 18 cm 3-10 20 cm 3 by changing the oxygen partial pressure during film growth.The conduction shows variable range hopping at low temperature and thermal activation conduction at high temperature.The ferromagnetism can be maintained up to room temperature.However,the anomalous Hall effect is observed only at low temperature and disappears above 160 K.This phenomenon can be attributed to the local ferromagnetism and the decreased optimal hopping distance at high temperatures.
文摘On the insulating side of the metal-insulator transition (MIT), the study of the effect of low Temperatures T on the electrical transport in amorphous silicon-nickel alloys a-Si1-yNiy:H exhibits that the electrical conductivity follows, at the beginning, the Efros-Shklovskii Variable Range Hopping regime (ES VRH) with T-1/2. This behaviour showed that long range electron-electron interaction reduces the Density Of State of carriers (DOS) at the Fermi level and creates the Coulomb gap (CG). For T higher than a critical value of temperature TC, we obtained the Mott Variable Range Hopping regime with T-1/4, indicating that the DOS becomes almost constant in the vicinity of the Fermi level. The critical temperature TC decreases with nickel content in the alloys.
基金Project supported by the National Key R&D Program of China(Grant No.2016YFA0200503)the National Natural Science Foundation of China(Grant No.61327813)
文摘We demonstrate transitions of hopping behaviors for delocalized electrons through the discrete dopant-induced quantum dots in n-doped silicon junctionless nanowire transistors by the temperature-dependent conductance characteristics.There are two obvious transition platforms within the critical temperature regimes for the experimental conductance data,which are extracted from the unified transfer characteristics for different temperatures at the gate voltage positions of the initial transconductance gm peak in Vg1 and valley in Vg2. The crossover temperatures of the electron hopping behaviors are analytically determined by the temperature-dependent conductance at the gate voltages Vg1 and Vg2. This finding provides essential evidence for the hopping electron behaviors under the influence of thermal activation and long-range Coulomb interaction.
文摘In this paper, we discuss low-temperature hopping-conductivity behavior in the insulating phase, in the absence of a magnetic field. We conduct a theoretical study of the crossover from hopping to activated transport in a GaAs two-dimensional hole system at low temperatures, finding that a crossover takes place from the Efros-Shklovskii variable-range hopping(VRH)regime to an activated regime in this system. This conductivity behavior in p-GaAs quantum wells is qualitatively consistent with the laws laid down in theories of localized electron interactions. Given sufficiently strong interactions, the holes in the localized states are able to hop collectively.
文摘We reanalyzed experimental data already published in Friedman J R, Zhang Y, Dai P, et al. Phys Rev B, 1996, 53（15）： 9528. Variable range hopping （VRH） conduction in the insulating three-dimensional n-CdSe samples has been studied over the entire temperature range from 0.03 to 1 K. In the absence of a magnetic field, the low temperature conductivity a of the three samples （A, B and C） obeys the Mott VRH conduction with an appropriate temperature dependence in the prefactor （a = σ0 exp [- （T0/T）]^p with p ≈ 0.25）. This behavior can be explained by a VRH model where the transport occurs by hopping between localized states in the vicinity of the Fermi level, EF, without creation of the Coulomb gap （CG）. On the contrary, no Efros-Shklovskii VRH is observed, suggesting that the density is constant in the vicinity of the EF.
文摘通过电阻率-温度(temperature dependence of resistivity,ρ-T)曲线、磁化强度-温度(temperature depen-dence of magnetization,M-T)曲线、ESR谱线的测量,研究了La0.45Ca0.55MnO3样品的电磁特性。结果表明,样品在整个测量温区呈现绝缘体行为,输运机制满足可变程跃迁模型。样品存在电荷有序(charge ordering,CO)相,相变温度TCO≈240K,并随温度降低发生顺磁(paramagnetism,PM)→电荷有序(CO)→反铁磁(antiferromagnetism,AFM)变化。值得注意的是,由于样品低温下存在多种复杂的磁相互作用,在40K发生自旋玻璃转变,表现为再入型自旋玻璃行为。
文摘为了有效地解决多跳频信号的盲源分离问题,提出了一种变步长的EASI(Equivariant Adaptive Separation via Independence)盲源分离算法。该算法在传统EASI算法的等变化性基础上,用性能指标(串音误差)作为准则,通过改变函数的取值范围及形状,自适应更新步长,使其在一个固定小的范围内,达到算法收敛速度和稳定性能的一个较理想的平衡点,改善了当步长固定时存在的缺陷。经过实验仿真,证明该算法对步长有很好的调整能力,性能稳定且收敛速度较快,能很好地将多个跳频信号进行分离,较传统的EASI算法有更高的适用性。
文摘提出一种单相电源供电时适用于异步电机传动的单相–三相变换器。由于仅采用7个晶闸管和1个移相电容,该变换装置具有造价低、结构简单的特点。分析该变换器的工作原理及开关过程,并提出一种基于开环变压变频(variable voltage variable frequency,VVVF)和变压恒频(variable voltage constant frequency,VVCF)控制的单相–三相离散跳频控制策略,用于电机的起动和稳态运行控制,一方面保证了电机在低频阶段足够大的起动力矩,另一方面可使电机稳步起动到额定转速。仿真和实验结果表明了该控制策略的有效性以及系统方案的可行性。
