Excited states of two-dimensional hydrogen atom in tilted magnetic field: Quantum chaos

The aim of the current work is the research of the influence of a tilted magnetic field direction on the spectrum and the energy level spacing distribution of a two-dimensional (2D) hydrogen atom and of an exciton in GaAs/Al_0.33Ga_0.67As quantum well. It was discovered that the quantum chaos (QC) is initiated with an increasing angle α between the magnetic field direction and the normal to the atomic plane. It is characterized by the repulsion of levels leading to the eliminating of the shell structure and by changing the spectrum statistical properties. The statement about the initiation of chaos and its dominance over regular motion with increasing angle α is confirmed by the results of our calculations of the classical dynamics presented in this paper. The evolution of the spatial distribution of the square of the absolute value of the wave function at an increasing angle α was observed. The differences of calculated dependencies of energies for various excited states on the tilt angle at a wide range of the magnetic field strength were described.     

Quantum phase transitions in mesoscopic Rashba rings

Novel quantum phases are found in the ground state of Rashba ring: the orbital magnetic phase (OMP), non-OMP, pseudo-OMP and quasi-OMP, which depend on the spin-orbit interaction (SOI) strength, electron number and ring size. We give the phase diagram and their quantum-phase-transition conditions.     

Anomalous hysteretic phenomena in cyclotron resonance spectra of GaAs/AlGaAs quantum well under tilted magnetic fields of short pulse up to 150 T

We observed a new type of hysteresis in cyclotron resonance spectra of two-dimensional electron gas confined in GaAs/AlGaAs multi quantum wells when we applied high magnetic fields tilted from the growth direction. Pulsed high magnetic fields up to 150 T were generated by the single turn coil technique. We investigated in detail the condition for the occurrence of the hysteresis which is a disagreement between two traces in the up- and down-sweeps of the pulsed magnetic fields. The dependencies of the hysteresis on the wavelength, sweep rate of the fields and temperature has led to the conclusion that the hysteresis is due to inequilibrium states in the up-sweep of tilted magnetic fields. The relaxation time from inequilibrium to equilibrium states was revealed to be of the order of microsecond.     

亥姆霍兹线圈磁场均匀范围的研究

推导了双环电流磁感应强度在直角坐标系中的解析式,将公式无量纲化,通过第一类和第二类完全椭圆积分计算场强的两个分量,从而计算合场强,画出亥姆霍兹线圈内外磁感应强度合场强曲面和三维均匀区域,发现磁场的均匀区域是"八爪"形状,并与双环电流不同距离的场强和均匀范围进行了比较.     

Electronic structures of GaAs/AlGaAs concentric double rings in applied electric and magnetic field

The electronic structures of GaAs/Al_0.35Ga_0.65As concentric double rings are calculated based on the effective mass envelope function theory, with and without the applied electric and magnetic field along the growth direction. The Hamiltonian matrix elements are determined through the Fourier transform method. As the heterostructure evolves from a single ring to the concentric double rings, our simulation is performed on the bound state energies of the electron and the hole. The results show that the energy levels undulate with the evolution of the ring. The applied magnetic field increases the ground state energies both of the electron and of the hole, as well as the transition energy between the first conduction subband and valence subband. However, the electric field decreases the electronic energies linearly.     

Optical and electronic properties of anisotropic parabolic quantum disks in the presence of tilted magnetic fields

In the present work, the electronic and optical properties of anisotropic parabolic quantum disks are studied in the presence of an applied magnetic field. For this goal, we first obtain the electron energy levels of an anisotropic parabolic quantum disk under axial, tilted, and in-plane magnetic fields. According to the results obtained for the energy levels reveal that there is no degeneracy at zero magnetic field due to symmetry breaking. With increasing the anisotropy, the energy level spacing increases. At a constant anisotropy, the energy levels splitting decreases with increasing tilt angle of magnetic field. The total refractive index changes decrease when the tilt angle of magnetic field and the anisotropy increase. Also, the total absorption coefficients increase as the tilt angle of magnetic field and anisotropy increase.     

磁场下含结构缺陷多组分超晶格中的局域电子态和电子输运

在有效质量近似理论下，利用转移矩阵和有效垒高方法研究了有限磁场下含结构缺陷的多组分超晶格中局域电子态的性质.在考虑各组分层有效质量的失配时，外加磁场会导致磁耦合效应的出现.磁耦合效应不仅引起局域电子能级的量子化，并且随着朗道指数或磁场强弱的变化，局域能级及其局域程度都会发生显著移动，特别是对高能区域的局域电子态影响更大.此外，还计算了电子输运系数，讨论了含结构缺陷的三组分超晶格中局域电子能级与输运谱透射禁区中的共振透射峰的关系，发现两者之间有着很好的对应关系，为相应的实验研究提供了依据. 关键词： 超晶格 局域电子态 磁场     

Tilted electric field effects on the electronic states in a GaAs quantum disk

In the present work we report the effects of a geometrical confinement and tilted applied electric field on the electronic energy levels in a semiconducting quantum disk. Calculations are performed in the effective mass approximation and using a variational method. The results can be summarized as follows: (1) due to the infinite confinement along the all directions of the heterostructure, the variational calculation with two parameters for tilted applied electric field can be treated with two independent each other variational parameters; (2) the magnitude of the energy shift is an increasing function of the applied electric field; (3) the effects of the applied electric field are magnified as the dimensions of the heterostructure (height and radius) grow; and finally (4) for large enough applied electric field the energy shift is a linear function of the applied electric field.     

Quantum transport in coupled resonators enclosed synthetic magnetic flux

Quantum transport properties are instrumental to understanding quantum coherent transport processes. Potential applications of quantum transport are widespread, in areas ranging from quantum information science to quantum engineering, and not restricted to quantum state transfer, control and manipulation. Here, we study light transport in a ring array of coupled resonators enclosed synthetic magnetic flux. The ring configuration, with an arbitrary number of resonators embedded, forms a two-arm Aharonov–Bohm interferometer. The influence of magnetic flux on light transport is investigated. Tuning the magnetic flux can lead to resonant transmission, while half-integer magnetic flux quantum leads to completely destructive interference and transmission zeros in an interferometer with two equal arms.     

Transport properties of mesoscopic graphene rings

Based on a recursive Green's function method, we investigate the conductance of mesoscopic graphene rings in the presence of disorder, in the limit of phase coherent transport. Two models of disorder are considered: edge disorder and surface disorder. Our simulations show that the conductance decreases exponentially with the edge disorder and the surface disorder. In the presence of flux, a clear Aharonov-Bohm conductance oscillation with the period Φ₀ (Φ₀=h/e) is observed. The edge disorder and the surface disorder have no effect on the period of AB oscillation. The amplitudes of AB oscillations vary with gate voltage and flux, which is consistent with the previous results. Additionally, ballistic rectification and negative differential resistance are observed in I-V curves, with on/off characteristic.     

Quantum Hall effect in back-gated InAs/GaSb heterostructures under a tilted magnetic field

We investigate the quantum Hall effect (QHE) in the InAs/GaSb hybridized electron–hole system grown on a conductive InAs substrate which act as a back-gate. In these samples, the electron density is constant and the hole density is controlled by the gate-voltage. Under a magnetic field perpendicular to the sample plane, the QHE appears along integer Landau-level (LL) filling factors of the net-carriers, where the net-carrier density is the difference between the electron and hole densities. In addition, longitudinal resistance maxima corresponding to the crossing of the extended states of the original electron and hole LLs make the QHE regions along integer-ν_net discontinuous. Under tilted magnetic fields, these R_xx maxima disappear in the high magnetic field region. The results show that the in-plane magnetic field component enhances the electron–hole hybridization and the formation of minigaps at LL crossings.     

Excitonic transitions in semiconductor concentric quantum double rings

Quantized energy levels of nanoscopic concentric double rings are identified by means of micro photoluminescence spectroscopy. High-yield emissions from a single quantum structures are observed. The spectra show several discrete lines reflecting the carrier confinement in the rings. Effective mass calculation is performed to characterize the quantized motion of carriers with rotational and orbital degrees of freedoms. Excellent agreement between the observed spectra and the numerical ones is found.     

Stability of soliton lattice phase in the bilayer quantum Hall state under tilted magnetic fields

The bilayer quantum Hall (QH) state at the filling factor ν=1 shows various fascinating quantum phenomena due to the layer degree of freedom called ‘pseudospin’. We report an experimental evidence of the soliton lattice (SL) phase, which is a domain structure of pseudospin, by the appearance of a local maximum of magnetoresistance near the ν=1 QH state. We investigate the stability of the SL phase by changing B and the total electron density n_T. Detailed magnetotransport measurements under tilted magnetic fields were carried out to obtain a B–n_T plane phase diagram containing the C, IC and SL phases. We found the SL phase is only stable at low n_T region. Namely, the C–SL–IC phase transition occurs only at low n_T region as B increases. On the contrary, the C–IC phase transition directly occurs without passing through the SL phase at high n_T region.     

Dynamics of nuclear spins appearing in transport measurements of an inter-edge spin diode in tilted magnetic fields

In a wide range of magnetic fields nonlinear transport between spin polarized edge channels is studied. The observed hysteresis of the I–V characteristic is attributed to the dynamic nuclear spin polarization due to the electronic spin-flip processes. We find extremely long nuclear spin relaxation times in the regime where the hyperfine interaction with electrons is switched off.     

Correlated electron states at level crossings of bilayer two-dimensional electron systems in tilted magnetic fields

We have measured the energy-level structure of high mobility, strongly coupled bilayer two-dimensional electron systems in tilted magnetic fields by means of magnetotransport experiments. At tilt angles where single-particle levels with opposite spin and symmetry cross, we observe a surprising sudden broadening of the quantum Hall plateaus and a deepening of the Shubnikov–de Haas minima. This observation is explained by an interaction-induced rearrangement of the energy level structure which strongly increases the energetic splitting of two (anti-)crossing levels.     

Quantum interference rectifier

Electron transport in bent quantum wire in the presence of a magnetic field which is orthogonal to the system plane is considered. Possible constructions of “quantum interference switch” and “quantum interference rectifier” are suggested.     

Raman study of Si–Ge intermixing in Ge quantum rings and dots

The Ge/Si (1 0 0) nanostructures have been studied by atomic force microscopy (AFM) and Micro Raman optical spectroscopy. Two layers of Ge of total thickness 0.75 nm and Si cap with thickness 2.5 nm were deposited by the method of molecular beam epitaxy at the temperature range 640–700 °C. AFM shows both quantum dots and ring-shape Ge nanostructures. From the analysis of the intensity and energy shift of the Raman signal we have found that the average concentration of Ge decreases considerably from 44% to 27%, when the growth temperature increases, whereas the degree of strain relaxation remains roughly the same. This allows us to conclude that intermixing is a dominating mechanism for strain relaxation in processes of transformation of Ge quantum dots to quantum rings.     

强磁场下的科学研究

文章介绍了强磁场在半导体物理、低维物理、高温超导体、重费米子、磁学、原子分子物理、化学、有机化合物、材料科学、微重力、核磁共振等领域中的重要作用.     

Studying quantum current magnification in mesoscopic coupling metallic rings

We propose a quantum Hamiltonian and obtain the relationship between external magnetic field and currents of three mesoscopic coupling rings. The impact of coupling on quantum current magnification in the system is studied. It is found that the quantum current magnification effect strongly depend on both the external magnetic flux and the coupling factors. As a result, by taking use of coupling rings, we can design some circuits to transfer and communicate signals.