Collective electron transport causes a weakly coupled semiconductor superlattice under dc voltage bias to be an excitable system with $2N+2$ degrees of freedom: electron densities and fields at $N$ superlattice periods plus the total current and the field at the injector. External noise of sufficient amplitude induces regular current self-oscillations (coherence resonance) in states that are stationary in the absence of noise. Numerical simulations show that these oscillations are due to the repeated nucleation and motion of charge dipole waves that form at the emitter when the current falls below a critical value. At the critical current, the well-to-well tunneling current intersects the contact load line. We have determined the device-dependent critical current for the coherence resonance from experiments and numerical simulations. We have also described through numerical simulations how a coherence resonance triggers a stochastic resonance when its oscillation mode becomes locked to a weak ac external voltage signal. Our results agree with the experimental observations.
Electron transmission through semiconductor superlattices is studied with transfer matrix method and resonance theory. The formation of electron band-pass transmission is ascribed to the coupling of different modes in those semiconductor superlattices with the symmetric unit cell. Upon Fabry-Pérot resonance condition, Bloch modes and two other resonant modes are identified to be related to the nature of the superlattice and its unit cell, respectively. The bands related to the unit cell and the superlattice overlap spontaneously in the tunneling region due to the shared wells, and the coupling…
The exciton absorption coefficient is determined analytically for a semiconductor superlattice in crossed electric and magnetic fields, for the magnetic field being parallel and the electric field being perpendicular to the superlattice axis. Our investigation applies to the case where the magnetic length, while being much smaller than the exiton Bohr radius, considerably exceeds the superlattice period. The optical absorption in superlattices displays a spectral fine structure related to the sequences of exciton states bound whose energies are adjacent to the Landau energies of the charge car…
Interlayer coupling in ferromagnetic semiconductor superlattices
本文发展了稀磁半导体载流子感生铁磁性的平均场论。我们的方法代表了一个标准的RKKY模型的改进，允许系统的空间不均匀性，自由载流子自旋极化，有限的温度，自由载流子交换和相关性要考虑自洽。作为一个例子，我们计算了Mn $_x$ Ga $_{1-x}$ As/GaAs超晶格的电子结构，证明了半导体磁电阻系统具有设计特性的可能性。
In semiconductor superlattices, when Bragg oscillating electrons interact with an input electromagnetic field, frequency multiplication is possible. An ideal superlattice has a purely antisymmetric voltage current response and can thus produce only odd harmonics. However, real world superlattices can also have even harmonic response and that increases the range of possible output frequencies. These effects have been recently explained with a predictive model that combines an Ansatz solution for the Boltzmann Equation with a Nonequilibrium Green's Functions approach. This predictive tool, coupl…
Weakly coupled semiconductor superlattices under dc voltage bias are excitable systems with many degrees of freedom that may exhibit spontaneous chaos at room temperature and act as fast physical random number generator devices. Superlattices with identical periods exhibit current self-oscillations due to the dynamics of charge dipole waves but chaotic oscillations exist on narrow voltage intervals. They disappear easily due to variation in structural growth parameters. Based on numerical simulations, we predict that inserting two identical sufficiently separated wider wells increases superlat…
In twisted homobilayer transition metal dichalcogenides, intra- and inter-layer valley excitons hybridize with the layer configurations spatially varying in the moiré. The ground state valley excitons are trapped at two high-symmetry points with opposite electric dipoles in a moiré supercell, forming a honeycomb superlattice of nearest-neighbor dipolar attraction. We find that the spatial texture of layer configuration results in a luminescence anomaly of the moiré trapped excitons, where a tiny displacement by interactions dramatically increases the brightness and changes polarization from ci…
When quantized, traces of classically chaotic single particle systems include eigenvalue statistics and scars in eigenfuntions. Since 2001, many theoretical and experimental works have argued that classically chaotic single electron dynamics influences and controls collective electron transport. For transport in semiconductor superlattices under tilted magnetic and electric fields, these theories rely on a reduction to a one-dimensional self-consistent drift model. A two-dimensional theory based on self-consistent Boltzmann transport does not support that single electron chaos influences colle…
