Magnetoresistance of a two-dimensional electron gas in a parallel magnetic field

The conductivity of a two-dimensional electron gas in a parallel magnetic field is calculated. We take into account the magnetic-field-induced spin-splitting, which changes the density of states, the Fermi momentum, and the screening behavior of the electron gas. For impurity scattering, we predict a positive magnetoresistance for low electron density and a negative magnetoresistance for high electron density. The theory is in qualitative agreement with recent experimental results found for Si inversion layers and Si quantum wells.     

Conductance asymmetry of a slot gate Si‐MOSFET in a strong parallel magnetic field

We report measurements on a Si‐MOSFET sample with a slot in the upper gate, allowing for different electron densities n_1,2 across the slot. The dynamic longitudinal resistance was measured by the standard lock‐in technique, while maintaining a large DC current through the source‐drain channel. We find that the conductance of the sample in a strong parallel magnetic field is asymmetric with respect to the DC current direction. This asymmetry increases with magnetic field. The results are interpreted in terms of electron spin accumulation or depletion near the slot.     

Magnetoresistance of two-dimensional tight-binding electrons in a weak magnetic field

We study the Anderson model on a two-dimensional square lattice with an applied weak magnetic field B which causes the hopping matrix elements to have Peierls phase factors. The recursion method is applied and B dependent conductivity σ(B) is calculated from the Kubo formula for different system sizes N and degree of disorder W. For large W there is no appreciable change of σ(B) with B, but its system size dependence is first an increasing and then a decreasing behavior.     

Rashba effect in an asymmetric quantum dot in a magnetic field

We derive an expression for the total spin-splitting energy in an asymmetric quantum dot with ferromagnetic contacts, subjected to a transverse electric field. Such a structure has been shown by one of us to act as a spintronic quantum gate with in-built qubit readers and writers (Phys. Rev. B61, 13813 (2000)). The ferromagnetic contacts result in a magnetic field that causes a Zeeman splitting of the electronic states in the quantum dot. We show that this Zeeman splitting can be finely tuned with a transverse electric field as a result of nonvanishing Rashba spin–orbit coupling in an asymmetric quantum dot. This feature is critical for implementing a quantum gate.     

The equatorial asymmetry of a magnetic field

Solution of the inverse problem for Parker’s one-dimensional mean-field dynamo model in a thin spherical layer is considered. The method allows the spatial distribution of energy sources, the α- and Ω-effects, to be found provided specified constraints occur on the solution. The highest ratio of the magnetic energies for the Northern and Southern hemispheres is discussed as such a constraint. The method is a modification of the Monte-Carlo technique; it is convenient for parallel computations and based on minimization of the cost function that characterizes the deviation of the model solution properties from the desired ones. The calculations show that the ratio of the energies in the hemispheres may exceed an order of magnitude for both poloidal and toroidal components of the magnetic energy. The ratio depends on the distance of the effective zone of the generation of the magnetic field from the equator and the number of harmonics in the spectrum. The greater this distance is and the higher the number of harmonics is, the stronger the magnetic field asymmetry can be.     

Two-dimensional metal in a parallel magnetic field

We have investigated the effect of an in-plane parallel magnetic field (B(axially) on two high mobility metallic-like dilute two-dimensional hole gas systems in GaAs quantum wells. The experiments reveal that, while suppressing the magnitude of the low temperature resistance drop, B(axially) does not affect E(a), the characteristic energy scale of the metallic resistance drop. The field B(c) at which the metallic-like resistance drop vanishes is dependent on both the width of the quantum well and the orientation of B(axially). It is unexpected that E(a) is unaffected by B(axially) up to B(c) despite the fact that the Zeeman energy at B(c) is roughly equal to E(a).     

Surface plasmon in a parallel magnetic field

Using a hydrodynamic model the dispersion relation for the surface plasmon is calculated in an external magnetic field parallel to the surface when the wave propagates perpendicular to the magnetic field. In the limit of zero wave vector, the results reduce to those of Chiu and Quinn who have used the dielectric constant in the local theory.     

Magnetoresistance of LaCoO3 and an insulator-metal transition induced in it by a high magnetic field

JETP Letters - The transformation of the band structure of LaCoO3 in the applied magnetic field has been theoretically studied. If the field is below its critical value B C ≈ 65 T, the...     

磁场下非对称T型量子波导的电子输运行为

运用模匹配方法和求解单电子薛定谔方程,来演示非对称T型磁量子结构的电子输运性质.结果表明,结构因子和磁势垒都能改变电子散射模数,电子输运谱因此变得复杂而丰富,散射区域出现了完全局域态和磁边缘态.在特定的结构参数和磁场强度下,能观测到宽谷、尖峰、共振透射和共振反射等电子输运现象,即可以通过调节磁场大小和结构参数来实现波矢过滤. 关键词： 介观体系 电子输运 磁效应     

Magnetoresistance of lightly doped TmBa2Cu3Ox crystals. Reorientation of the antiferromagnetic structure in a magnetic field

The magnetoresistance of lightly doped TmBa₂Cu₃O_x single crystals is investigated in the temperature range 4.2–300 K for magnetic fields up to 12 T. For the antiferromagnetic sample (x=6.3), when the current and field lie in the ab plane, the magnetoresistance is the sum of an anisotropic and a background component. The existence of the anisotropic component is attributed to the restructuring of the antiferromagnetic domain structure in a magnetic field. Pis’ma Zh. éksp. Teor. Fiz. 70, No. 5, 350–355 (10 September 1999)     

Wigner liquid conductivity in a parallel magnetic field

It is assumed that comparatively low-mobility objects (clusters of a small number of electrons) can appear in a two-dimensional strongly correlated electronic system (Wigner liquid) against the background of mobile Fermi-type carriers. These formations can get “pinned” to inhomogeneities and play the role of additional scatterers. Clusters of two and three electrons are discussed (for a short-range order in the arrangement of electrons, as in a triangular lattice). The number of these clusters depends on both temperature and the parallel magnetic field. This results in the temperature and field dependences of the resistance and magnetization of the system. According to a simple model, resistance increases and the metal-dielectric transition occurs as the parallel magnetic field grows stronger. The model predicts a nonlinear magnetic field dependence of magnetization.     

System of quantum wells in a parallel magnetic field

The energy spectrum and quantum states of electrons in a system of quantum wells in a strong magnetic field parallel to the heterogeneous boundaries are studied. The combined effect of the quantizing magnetic field and the potential of the system of quantum wells leads to a radical change in the electron dispersion relation owing to the appearance of one-dimensional Landau bands. The neighborhoods of the anticrossing points of the different bands correspond to an effective redistribution of the electron envelope functions, which becomes stronger as the magnetic field is raised. The character of the electron-state density in the size-quantization subbands is examined qualitatively in connection with the change in the system of isoenergy contours when a magnetic field is applied. Fiz. Tverd. Tela (St. Petersburg) 40, 1719–1723 (September 1998)     

Axial-homogeneous oscillations in semiconductor rod with an arbitrary direction of the magnetic field

Theoretical and numerical studies of the electromagnetio properties of the semiconductor rod with an arbitrary direction of the external magnetic field was carried out. It was investigated new types of surface oscillations in semiconductor rod and the regions of their existence with help of exact dispersion equation. It was considered unreciprocal effect at the deviation of external magnetic field direction into opposite.     

相互作用量子点系统中的场致自旋电流

从理论上研究了相互作用量子点在外部旋转磁场下的非平衡自旋输运性质，研究结果表明，量子点中的相干自旋振荡可以导致自旋电流的产生，当计入库仑关联相互作用后，近藤共振效应受外部进动磁场的影响很强，特别是当磁场的进动频率与塞曼能移满足共振条件时，每个自旋近藤峰就会劈裂为两个自旋共振峰的叠加，在低温强耦合区，这种近藤型共隧穿过程对自旋电流带来重要贡献。     

Spin current through a quantum dot in the presence of an oscillating magnetic field

Nonequilibrium spin transport through an interacting quantum dot is analyzed. The coherent spin oscillations in the dot provide a generating source for spin current. In the interacting regime, the Kondo effect is influenced in a significant way by the presence of the processing magnetic field. In particular, when the precession frequency is tuned to resonance between spin-up and spin-down states of the dot, Kondo singularity for each spin splits into a superposition of two resonance peaks. The Kondo-type cotunneling contribution is manifested by a large enhancement of the pumped spin current in the strong coupling low temperature regime.     

Magnetic phase diagram of MnP: Field parallel to the hard direction

The phase diagram of MnP, for magnetic field parallel to the a axis, was determined. Three ordered phases were found. They are tentatively identified as ferromagnetic, fan, and cone phases. The triple point where the ferro, fan, and paramagnetic phases meet has features which are expected for a Lifshitz point.     

Broadening of the spectral line of spin self-oscillations in a nanocolumn magnetic structure upon magnetic field and current variations

The spin dynamics in a thin layer of a nanocolumn layered magnetic structure during the flow of a spin-polarized current in the presence of magnetic fluctuations is theoretically analyzed. Using the macrospin model, the frequency and Q factor of the spin oscillations are calculated as functions of the spin-polarized current upon the occurrence of current self-generation.     

Photogalvanic effect in an asymmetric system of three quantum wells in a strong magnetic field

The photogalvanic effect (PGE) in an asymmetric undoped system of three GaAs/AlGaAs quantum wells illuminated with white light of various intensities is investigated in magnetic fields up to 75 kOe at temperatures ranging from 4.2 K up to 300 K. A maximum of the spontaneous photogalvanic current J ^PGE as a function of the magnetic field predicted by A. A. Gorbatsevich et al., JETP Lett. 57, 580 (1993), is observed. Analysis of the experimental data shows that the main initial characteristic of the PGE is not the spontaneous current but rather the electromotive force E ^PGE arising in the direction perpendicular to the applied magnetic field. It is determined that this emf is independent of the intensity of the incident light, increases linearly with the size d of the illuminated region, and decreases slowly with temperature: E _max ^PGE ∼0.8 V at 300 K and ∼0.1 V at 4.2 K for d∼3 mm. The curve E ^PGE(H) at room temperature is determined with allowance for the strong transverse magnetoresistance of the nanostructure. Pis’ma Zh. éksp. Teor. Fiz. 63, No. 3, 197–202 (10 February 1996)