Spin-orbit coupling and resonances in the conductance of quantum wires
We investigate a possibility of pair electron-electron (e−e) collisions in a ballistic wire with spin-orbit coupling and only one populated mode. Unlike in a spin-degenerate system, a combination of spin splitting in momentum space with a momentum-dependent spin precession opens up a finite phase space for pair e−e collisions around three distinct positions of the wire's chemical potential. For a short wire, we calculate the corresponding resonant contributions to the conductance, which have different power-law temperature dependencies, and, in some cases, vanish if the wire's transverse confinement potential is symmetric. Our results may explain the recently observed feature at the lower conductance plateau in InAs wires.
A model of inhomogeneous pores filling during electrodeposition of ordered metal nanowire arrays isdeveloped. The model takes into consideration the ionic transfer both in the varying diffusion layer in thepores and in the diffusion layer above the template, which is determined by the external hydrodynamicconditions. The model takes into account the kinetics of electrochemical reaction (the Tafel equation)and the diffusion transfer of metal cations both in the pores and in the outer diffusion layer. In the quasi-steady-state approximation, two problems were considered. The problem for the case that the initiallength of one pore differs from that of all other pores is solved analytically. The problem for the case thatthe initial lengths of all pores are different is solved numerically. The time dependences of unfilled porelength are obtained for various overpotentials and various initial distributions of pore length. It is foundthat the pores filling inhomogeneity increases with increasing overpotential.
Ensembles of Nanowires (NW) of iron group metals-pure metals (Fe, Ni and Co) and their alloys (Fe-Ni, Fe-Co) were obtained using matrix synthesis technique based on polymer track matrixes. Compositions of electrolytes were chosen – the salt of one corresponding metal (in the first case) and two salts (for second case). The galvanic process was investigated and it was found that it consists of different stages. Deposition of metal inside the pores has non-linear character due to diffusion limitation. The specific features of the next part (formation and growing of the “caps”) was also studied. Electron microscopy, X-rays analysis, Mössbauer spectroscopy and magnetic hysteresis were applied to investigate the dependence of structure and magnetic properties of the NW on electrodeposition conditions. It was found that the composition of two-component NWs differs from the composition of electrolyte and different at different parts of NW. Mössbauer spectroscopy gave possibility to estimate hyperfine parameters for Fe-Co NWs. For Fe-Ni NWs it was supposed that the spectra could be presented as superposition of at least three magnetic sextets with hyperfine parameters Bhf 27-33 T. It was shown that Fe-Co samples have “hard magnetic” properties, while Fe-Ni samples have “soft magnetic” parameters. The dependence of these parameters on the synthesis was demonstrated.
Achievement of the ultimate sensitivity along with a high spectral resolution is one of the frequently addressed problems, as the complication of the applied and fundamental scientific tasks being explored is growing up gradually. In our work, we have investigated performance of a superconducting nanowire photon-counting detector operating in the coherent mode for detection of weak signals at the telecommunication wavelength. Quantum-noise limited sensitivity of the detector was ensured by the nature of the photon-counting detection and restricted by the quantum efficiency of the detector only. Spectral resolution given by the heterodyne technique and was defined by the linewidth and stability of the Local Oscillator (LO). Response bandwidth was found to coincide with the detector's pulse width, which, in turn, could be controlled by the nanowire length. In addition, the system noise bandwidth was shown to be governed by the electronics/lab equipment, and the detector noise bandwidth is predicted to depend on its jitter. As have been demonstrated, a very small amount of the LO power (of the order of a few picowatts down to hundreds of femtowatts) was required for sufficient detection of the test signal, and eventual optimization could lead to further reduction of the LO power required, which would perfectly suit for the foreseen development of receiver matrices and the need for detection of ultra-low signals at a level of less-than-one-photon per second.
A simple model of electrochemical growth of nanowires in the pores of anodic aluminum oxide (AAO) template is developed. The metal deposition is considered at various overpotentials. The model takes into consideration the ionic transfer both in the varying diffusion layer in the pores and in the diffusion layer above the template, which is determined by the external hydrodynamic conditions. The model takes into account the kinetics of electrochemical reaction by means of the Tafel equation and the diffusion transfer of metal cations both in the pores and in the outer diffusion layer. The analytical solution of the problem with several simplifications yields the equations for calculating the time dependence of current, the pore filling time, and other parameters of the process. An example of the application of the model for the analysis of nanowire growth in the template pores is compared with the experimental data showing good agreement.
We report preparation of nanoribbons (crossection ~ 250*25 nm2) by focused ion beam etching of single-crystalline Bi2Se3 and detailed measurements of their magnetoresistance at temperatures down to 4.2 K, magnetic field up to 9 T. In a magnetic field parallel to the axis of nanowire the magnetoresistance shows up oscillations. Surprisingly, the Fourier analysis shows the presence not only of oscillations with a period corresponding to the flux quantum (Φ0 = hc/e), but also oscillations with a period of 2Φ0 and 4Φ0. Possible mechanisms of the observed effect are discussed.
The dynamics of a two-component Davydov-Scott (DS) soliton with a small mismatch of the initial location or velocity of the high-frequency (HF) component was investigated within the framework of the Zakharov-type system of two coupled equations for the HF and low-frequency (LF) fields. In this system, the HF field is described by the linear Schrödinger equation with the potential generated by the LF component varying in time and space. The LF component in this system is described by the Korteweg-de Vries equation with a term of quadratic influence of the HF field on the LF field. The frequency of the DS soliton`s component oscillation was found analytically using the balance equation. The perturbed DS soliton was shown to be stable. The analytical results were confirmed by numerical simulations.
Radiation conditions are described for various space regions, radiation-induced effects in spacecraft materials and equipment components are considered and information on theoretical, computational, and experimental methods for studying radiation effects are presented. The peculiarities of radiation effects on nanostructures and some problems related to modeling and radiation testing of such structures are considered.