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[en] We calculate the non-symmetrized finite-frequency NS-FF noise for a single-level quantum dot connected to reservoirs in the spinless non-interacting case. The calculations are performed within the framework of the Keldysh Green’s function formalism in the wide band approximation limit. We establish the general formula for NS-FF noise for any values of temperature, frequency and bias voltage. The electron transfer processes from one to the other reservoir act via the transmission amplitude and transmission coefficient depending on the energy. By taking the symmetrized version of this expression, we show that our result coincides with the expression of the finite frequency noise obtained by Büttiker using the scattering theory. We also give the explicit analytical expression for the NS-FF noise in the zero temperature limit. Finally, by performing numerical calculations, we discuss the evolution of the NS-FF noise spectrum with varying temperature, dot energy level, and coupling strength to the reservoirs, revealing a large variety of behaviors such as different symmetry properties and changes of sign in the excess noise. (special issue on unsolved problems of noise in physics, biology and technology)
[en] A very efficiently finite element model is developed for static analysis of nanobeams. Nonlocal differential equation of Eringen is exploited to reveal a scale effect of nanobeams through nonlocal Euler-Bernoulli beam theory. The equilibrium equation of nonlocal beam is derived based on the variational statement. The element stiffness matrix and force vector are presented. The novelty and accuracy of this model is presented and verified. It is found that, this model is more accurate than others and can consider as a benchmark. The effects of nonlocality, boundary conditions, and slenderness ratio are figured out. The deflection of multi-span nanobeam is also illustrated. The present model can be used for static analysis of single-walled carbon nanotubes. Complex geometry and nonlinear boundary conditions can also be included.
[en] We report the prediction of quasibound states (resonant states with very long lifetimes) that occur in the eigenvalue continuum of propagating states for certain systems in which the continuum is formed by two overlapping energy bands. We illustrate this effect using a quantum wire system with two channels and an attached adatom. When the energy bands of the two channels overlap, a would-be bound state that lays just below the upper energy band is slightly destabilized by the lower energy band and thereby becomes a resonant state with a very long lifetime (a second such state lays above the lower energy band). Unlike the bound states in continuum predicted by von Neumann and Wigner, these states occur for a wide region of parameter space
[en] I explicitly construct a strong zero mode in the XYZ chain or, equivalently, Majorana wires coupled via a four-fermion interaction. The strong zero mode is an operator that pairs states in different symmetry sectors, resulting in identical spectra up to exponentially small finite-size corrections. Such pairing occurs in the Ising/Majorana fermion chain and possibly in strongly disordered many-body localized phases. The proof here shows that the strong zero mode occurs in a clean interacting system, and that it possesses some remarkable structure—despite being a rather elaborate operator, it squares to the identity. Eigenstate phase transitions separate regions with different strong zero modes. (letter)
[en] We would like to note that most of the results published in Li et al 2008 New J. Phys. 10 043007 agree with the results of Mueller and Kern 1996 Appl. Surf. Sci. 102 6 that do not appear to be widely known. (comment)
[en] We present a study on the magnetization reversal in Co/Pt multilayer films with an out-of-plane easy axis of magnetization deposited onto substrates with densely distributed perforations with an average period as small as 34 nm. Deposition of magnetic Co/Pt multilayers onto the nanoperforated surface results in an array of magnetic nanodots surrounded by a continuous magnetic film. Following the evolution of the magnetic domain pattern in the system, we suggest that domain walls are pinned on structural inhomogeneities given by the underlying nanoperforated template. Furthermore, a series of micromagnetic simulations was performed in order to understand the modification of the pinning strength of domain walls due to the magnetic interaction between nanodots and the surrounding film. The results of the simulations show that magnetic exchange coupling between the nanodots and the surrounding film strongly influences the pinning behavior of the magnetic domain walls which can be optimized to provide maximal pinning.
[en] Research highlights: → This paper is dedicated to structures based on Cd1-xZnxS. - Abstract: The present work reports on a theoretical investigation of superlattices based on Cd1-xZnxS quantum dots embedded in an insulating material. The system to model is assumed to be a series of flattened cylindrical quantum dots with a finite barrier at the boundary and is studied using a sinusoidal potential. The electronic states of both Γ1 - (ground) and Γ2 - (first excited) minibands have been computed as a function of inter-quantum dot separation and Zn composition. An analysis of the results shows that the widths of Γ1 - and Γ2 - minibands decrease as the superlattice period and Zn content increase separately. Moreover, the sinusoidal shape of the confining potential accounts for the coupling between quantum dots quantitatively less than the Kronig-Penney potential model.
[en] This book includes abstracts of the communications presented at the 5th International Conference on Materials Science and Condensed-Matter Physics and at the Symposium dedicated to the 100th anniversary of academician Boris Lazarenko, the prominent scientist and inventor, the first director of the Institute of Applied Physics of the Academy of Sciences of Moldova. The abstracts presented in the book cover a vast range of subjects, such as: advanced materials and fabrication processes; methods of crystal growth, post-growth technological processes, doping and implantation, fabrication of solid state structures; defect engineering, engineering of molecular assembly; methods of nanostructures and nano materials fabrication and characterization; quantum wells and superlattices; nano composite, nanowires and nano dots; fullerenes and nano tubes, molecular materials, meso- and nano electronics; methods of material and structure characterization; structure and mechanical characterization; optical, electrical, magnetic and superconductor properties, transport processes, nonlinear phenomena, size and interface effects; advances in condensed matter theory; theory of low dimensional systems; modelling of materials and structure properties; development of theoretical methods of solid-state characterization; phase transition; advanced quantum physics for nano systems; device modelling and simulation, device structures and elements; micro- and optoelectronics; photonics; microsensors and micro electro-mechanical systems; microsystems; degradation and reliability, solid-state device design; theory and advanced technologies of electro-physico-chemical and combined methods of materials machining and treatment, including modification of surfaces; theory and advanced technologies of using electric fields, currents and discharges so as to intensify heat mass-transfer, to raise the efficiency of treatment of materials, of biological preparations and foodstuff; modern equipment for electrical materials machining and treatment.
[en] The effects of magnetic field on the magnetic anisotropy of amorphous Co–Fe–B nanowire arrays during the electroless plating process have been investigated. The results show that the easy magnetization direction of the Co–Fe–B nanowire array rotated from in-plane to out-of-plane with the applied magnetic field increasing. A mechanism based on the variation of atomic short-range ordering induced by the applied magnetic field is proposed to interpret this unique anisotropy transformation. - Highlights: • Co–Fe–B nanowires with good quality are obtained by the electroless plating method. • The magnetic anisotropy is tailored by the magnetic field applied during plating. • Short-range order is proposed to explain this unique anisotropy transformation