Light absorption by a two-dimensional quantum dot superlattice

The monochromatic light absorption in an ideal two-dimensional quantum dot superlattice (QDSL) is considered theoretically. Calculations of the absorption coefficient are done in both the absence and presence of a homogeneous DC electric field with rational and irrational orientations. The explicit dependencies of the absorption coefficient on the frequency of the light, the QDSL parameters and the strength of the electric field are found. Some numerical results for GaAs—Ga_0.7Al_0.3As QDSL are obtained.     

Observation of quantum destructive interference in inelastic two-wave mixing

Using room-temperature 87Rb atoms we demonstrate a quantum destructive interference between two one-photon excitation pathways in an inelastic two-wave mixing scheme that corresponds to the "strong-storage and weak-retrieval" of an optical field. This destructive interference is fundamentally different from the usual electromagnetically induced transparency because it is critically dependent on the generation and propagation of a wave-mixing field. We also show that contrary to the common belief, the maximum atomic coherence in general does not lead to the maximum mixing-wave conversion efficiency.     

Isolated structures in two-dimensional optical superlattice

Overlaying commensurate optical lattices with various configurations called superlattices can lead to exotic lattice topologies and, in turn, a discovery of novel physics. In this study, by overlapping the maxima of lattices, a new isolated structure is created, while the interference of minima can generate various “sublattice” patterns. Three different kinds of primitive lattices are used to demonstrate isolated square, triangular, and hexagonal “sublattice” structures in a two-dimensional optical superlattice, the patterns of which can be manipulated dynamically by tuning the polarization, frequency, and intensity of laser beams. In addition, we propose the method of altering the relative phase to adjust the tunneling amplitudes in “sublattices”. Our configurations provide unique opportunities to study particle entanglement in “lattices” formed by intersecting wells and to implement special quantum logic gates in exotic lattice geometries.     

Strain-induced quantum dot superlattice

Coupled double quantum dots and quantum dot superlattices are formed by utilizing the strain of an InP island on top of a near-surface multi-quantum-well structure. The number and composition of the quantum wells together with the thickness of the barrier separating the quantum wells are varied to investigate the coupling of the wave functions of the carriers confined in separate vertically stacked dots. Photoluminescence studies show that the reduction of the barrier thickness and the increase of the number of wells enhance the coupling, which is observed as red shift and narrowing of the quantum dot peak. The calculated shifts of the peak positions agree closely with the experimental values.     

Structural instabilities of a two-dimensional Wigner crystal in a lateral superlattice

We consider the instability of a two-dimensional Wigner crystal in a short-period lateral superlattice. To find instabilities, we calculate the phonon spectrum of the electron lattice deformed by a periodic potential. We show that one of the transverse modes of the deformed electron crystal becomes soft when the electron density exceeds a critical value. This can result in a phase transition with the formation of a charge-density wave.     

Electron spectrum in a quantum superlattice with cylindrical symmetry

A quantum superlattice with axial symmetry, a heterostructure in which two semiconductor materials in the form of coaxial wires with a nanosize cross section are in contact with one another and form a periodic structure in the radial direction, is studied. It is shown that the electron energy spectrum consists of alternating allowed and forbidden bands. The electron dispersion law is studied for different values of the period of the potential, thicknesses of the semiconductor layers, and radius of the inner crystal of the system. It is shown that the coherent electron effective mass of the quantum superlattice is a tensor: The longitudinal component is close in value to the electron effective mass of the semiconductor material characterizing the quantum well of the superlattice and the radial component depends strongly on the period of the potential, the thicknesses of the coaxial semiconductor layers, and the core radius of the heterosystem, taking on positive or negative values in different allowed bands. Fiz. Tverd. Tela (St. Petersburg) 40, 557–561 (March 1998)     

Ratchet effects in quantum wells with a lateral superlattice

Experimental and theoretical works on the ratchet effects in quantum wells with a lateral superlattice excited by alternating electric fields of terahertz frequency range has been reviewed. We discuss the Seebeck ratchet effect and helicity driven photocurrents and show that the photocurrent generation is based on the combined action of a spatially periodic in-plane potential and a spatially modulated light.     

Quasiparticle states and quantum interference induced by magnetic impurities on a two-dimensional topological superconductor

We theoretically study the effect of localized magnetic impurities on two-dimensional topological superconductor (TSC). We show that the local density of states (LDOS) can be tuned by the effective exchange field m, the chemical potential μ of TSC, and the distance Δr as well as the relative spin angle α between two impurities. The changes in Δr between two impurities alter the interference and result in significant modifications to the bonding and antibonding states. Furthermore, the bound-state spin LDOS induced by single and double magnetic impurity scattering, the quantum corrals and the quantum mirages are also discussed. Finally, we briefly compare the impurities in TSC with those in topological insulators.     

Oscillations of the magnetoresistance of a two-dimensional electron gas in a GaAs quantum well with AlAs/GaAs superlattice barriers in a microwave field

The effect of microwave radiation in the frequency range from 1.2 to 10 GHz on the magnetoresistance of a high-mobility two-dimensional electron gas has been studied in a GaAs quantum well with AlAs/GaAs superlattice barriers. It has been found that the microwave field induces oscillations of this magnetoresistance, which are periodic in the reciprocal magnetic field (1/B). It has been shown that the period of these oscillations in the frequency range under study depends on the microwave radiation power.     

Effective generation of red-green-blue laser in a two-dimensional decagonal photonic superlattice

We demonstrate the effective generation of red, green and blue (RGB) light in a two-dimensional decagonal quasiperiodic LiNbO₃ nonlinear crystal. Owing to the unique abundance in reciprocal vectors (RVs), the RGB signals were generated directly by frequency doublings. Thus the conversion efficiencies of the RGB light were much higher than previously recorded. In addition, the same results were obtained when the crystal was rotated by integral multiples of π/5. This result will aid in the effective generation of RGB in multiple directions and may have important applications in laser-based projection displays. PACS 42.65.Ky; 42.72.Bj; 42.79.Nv     

Spectrum of an electron in a superlattice along a cylindrical quantum wire

The quasi-one-dimensional superlattice of two contacting semiconductor materials along a cylindrical quantum wire (using the example of CdS/HgS) is investigated. It is shown that the energy center of the electron is an alternation of allowed and forbidden bands. The dispersion law for different values of the period of the potential and the radius of the quantum wire is investigated. A transition to the Kronig-Penney model is obtained. The effective masses of the electrons of different bands are found. Chernovits State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 96–103, February, 1998.     

Electron transport across a quantum wire embedding a saw-tooth superlattice

By developing the recursive Green function method, the transport properties through a quantum wire embedding a finite-length saw-tooth superlattice are studied in the presence of magnetic field. The effects of magnetic modulation and the geometric structures of the superlattice on transmission coefficient are discussed. It is shown that resonant peak splitting of this kind of structure is different from that of ‘magnetic' and ‘electric' superlattices in two-dimensional electron gas. The transmission spectrum can be tailored to match requirements through adjusting the size of saw-tooth quantum dot and field strength.     

Observation of completely destructive quantum interference between interacting resonances in molecular predissociation

A unique observation is presented of interacting predissociating resonances which exhibit completely destructive interference in a region between the resonances. The use of a double-resonance technique, in which single rotational levels of the b (1)Sigma(+)(g) state of O2, prepared by pumping the magnetic-dipole b <--X transition, are probed by (2+1) resonance-enhanced multiphoton-ionization spectroscopy, eliminates overlapping rotational structure and enables observation of the interference process. Using a diabatic coupled-channel model, the interacting resonances are shown to be derived from the d (1)Pi(g)(v = 3,J = 17) Rydberg and II (1)Delta(g)(v = 6,J = 17) valence states.