Computer experiment on propagation of solitons in crystals

Molecular dynamics computer simulation was carried out for homogeneous one-dimensional crystals and Langmuir–Blogett chain crystals. A mass-spring model was used, and the anharmonic interatomic potential up to the fourth order was taken into account. The total number of atoms was 120, and an end of the crystal was free to move and the other end fixed. An input pulse was applied to a couple of free end atoms, and the displacements and kinetic energies of all atoms in the crystal were computed. Solitons and phonons were produced, propagated and reflected at the ends of the crystal. Long-period propagation of stable solitons was observed in homogeneous crystals and in one-layer LB chain crystals.     

Influence of hot Phonons on the Transport Properties of Single-Wall Carbon Nanotubes

We investigate the effects of hot phonons on the transport properties of metallic single-wall carbon nanotubes lying on a substrate. A deterministic numerical scheme is applied to solve the system of Boltzmann equations for electrons and phonons. The simulations demonstrate that the optical phonons are strongly driven out of thermal equilibrium and considerably influence the electron transport at high bias. Comparisons of the theoretical results with experimental current-voltage characteristics exhibit very good agreement.     

Raman Spectroscopy, Structural Modifications, and Phase Transitions in the High-Temperature Superconductors

The formation of phases is investigated from a systematic study of the Raman active phonons in the whole range of oxygen doping of YBa₂Cu₃O _x (6 < x < 7). Changes in the spectral characteristics of the in-phase vibrations of the plane oxygen atoms in the overdoped region are related, with slight modifications of the buckling in the CuO₂ planes. A softening of the A _g symmetry apical oxygen phonon is accompanied with an increase in the intensity of the high-frequency mode at 600 cm^–1 and attributed to the breaking of the chains into small segments. The analysis of the apex and the in-phase phonon modes indicates the formation of superstructures, which are embedded as spatially separated phases in the whole oxygen concentration region of 6.35 < x < 6.95. A similar separation into small domains of phases may also occur in the underdoped compounds (x < 6.35) down to a critical oxygen concentration at x 6.15, where the system breaks into randomly oriented small chains.     

Intersubband dynamics in modulation doped quantum wells

A theoretical investigation of the dynamics of intersubband transitions in modulation doped multiple narrow GaAs / Al_xGa_1−xAs quantum well structures by emission of GaAs (well) and Al_xGa_1−xAs (barrier) slab and interface mode polar optical phonons is presented. Photo-excited carrier behavior is interpreted via Monte Carlo simulations which predict long time constants for electron relaxation.     

声子之间相互作用和库仑势对量子点中束缚极化子性质的影响

研究了库仑场中抛物量子点中束缚极化子的性质,采用线性组合算符和微扰法,导出了量子点中束缚极化子的基态能量,在计及电子在反冲效应中发射和吸收不同波矢的声子之间的相互作用下,研究了其对量子点中束缚极化子的基态能量的影响。数值计算表明：当考虑声子之间的相互作用时,量子点中束缚极化子的基态能量随量子点的有效受限长度的减小而迅速增大,当l0〉1.0时,必须考虑声子之间的相互作用对基态能量的影响。     

声子之间相互作用对半导体量子点中磁极化子性质的影响

研究了半导体量子点中磁极化子的性质.采用线性组合算符和微扰法,导出了半导体量子点中磁极化子的基态能量.在计及电子在反冲效应中发射和吸收不同波矢的声子之间相互作用时,讨论了对半导体量子点中磁极化子的基态能量的影响.通过数值计算表明,半导体量子点中磁极化子的基态能量随量子点的有效受限长度的减小而迅速增大,随磁场的增加而增加,对于弱磁场声子之间相互作用的影响不能忽略.     

Phonon excitation of quasiparticles in niobium and tantalum superconducting tunnel junction photon detectors

We report phonon pulse measurements of quasiparticle (qp) self-recombination and trapping by Abrikosov vortices in Nb and Ta superconducting tunnel junctions. The quasiparticle loss times, determined from the shape of the tunnel junction output pulse, were found to be strongly correlated with flux trapping. The measured results were compared with the model of Golubov and Houwman. It was found that qp self-recombination, as measured from the dependence of responsivity on absorbed phonon energy, was also modified by the presence of traps. A process of phonon-mediated de-trapping is proposed to explain the observed effects.