Spin-orbit coupling and phase-coherence in InAs nanowires

We investigated the magnetotransport of InAs nanowires grown by selective area metal-organic vapor phase epitaxy. In the temperature range between 0.5 and 30 K reproducible fluctuations in the conductance upon variation of the magnetic field or the back-gate voltage are observed, which are attributed to electron interference effects in small disordered conductors. From the correlation field of the magnetoconductance fluctuations the phase-coherence length l_phi is determined. At the lowest temperatures l_phi is found to be at least 300 nm, while for temperatures exceeding 2 K a monotonous decrease of l_phi with temperature is observed. A direct observation of the weak antilocalization effect indicating the presence of spin-orbit coupling is masked by the strong magnetoconductance fluctuations. However, by averaging the magnetoconductance over a range of gate voltages a clear peak in the magnetoconductance due to the weak antilocalization effect was resolved. By comparison of the experimental data to simulations based on a recursive two-dimensional Green's function approach a spin-orbit scattering length of approximately 70 nm was extracted, indicating the presence of strong spin-orbit coupling.Comment: 8 pages, 7 figure

Superlattice with hot electron injection: an approach to a Bloch oscillator

A semiconductor superlattice with hot electron injection into the miniband is considered. The injection changes the stationary distribution function and results in a qualitative change of the frequency behaviour of the differential conductivity. In the regime with Bloch oscillating electrons and injection into the upper part of the miniband the region of negative differential conductivity is shifted from low frequencies to higher frequencies. We find that the dc differential conductivity can be made positive and thus the domain instability can be suppressed. At the same time the high-frequency differential conductivity is negative above the Bloch frequency. This opens a new way to make a Bloch oscillator operating at THz frequencies.Comment: RevTeX, 8 pages, 2 figures, to be published in Phys. Rev. B, 15 Januar 200

Suppressed absolute negative conductance and generation of high-frequency radiation in semiconductor superlattices

We show that space-charge instabilities (electric field domains) in semiconductor superlattices are the attribute of absolute negative conductance induced by small constant and large alternating electric fields. We propose the efficient method for suppression of this destructive phenomenon in order to obtain a generation at microwave and THz frequencies in devices operating at room temperature. We theoretically proved that an unbiased superlattice with a moderate doping subjected to a microwave pump field provides a strong gain at third, fifth, seventh, etc. harmonics of the pump frequency in the conditions of suppressed domains.Comment: 8 pages. Development of cond-mat/0503216 . Version 2: Final version, erratum is include

Проблемы проведения биоаналитической части исследований биоэквивалентности лекарственных препаратов в России

In the review of the main problems holding bioanalytical part of bioequivalence studies of medicines in Russia. The analysis of the major causes of failure when performing studies of bioequivalence and pharmacokinetics.В обзоре рассмотрены основные проблемы проведения биоаналитической части исследований биоэквивалентности лекарственных препаратов в России. Проведен анализ основных причин неудач при выполнении исследований по биоэквивалентности и фармакокинетике

Spin-orbit coupling and phase-coherent transport in InN nanowires

The low-temperature quantum transport properties of gated InN nanowires were investigated. Magnetic-field-dependent as well as gate-dependent measurements of universal conductance fluctuations were performed to gain information on the phase coherence in the electron transport. We found a pronounced decrease in the variance of the conductance by about a factor of 2 in gate-dependent fluctuation measurements if a magnetic field is applied. This effect is explained by the suppression of the Cooperon channel of the electron correlation contributing to the conductance fluctuations. Despite the fact that the diameter of the nanowire is less than 100 nm a clear weak antilocalization effect is found in the averaged magnetoconductance being in strong contrast to the suppression of weak antilocalization for narrow quantum wires based on planar two-dimensional electron gases. The unexpected robustness of the weak antilocalization effect observed here is attributed to the tubular topology of the surface electron gas in InN nanowires

Electrical properties of rolled-up p-type Si/SiGe heterostructures

We report a theoretical study of the hole density and the low-field mobility in modulation p-doped rolled-up Si/SiGe heterostructures. Solving coupled Poisson and Schrödinger equations, we show that the total hole density is strongly affected by charged surface states and can reach value of 1011 cm−2 for available doping level at room and low temperature. The simulation of the hole transport along the structure axis based on a Monte Carlo method reveals that the interface roughness scattering is a main mechanism limiting the mobility magnitude, which reaches the value of 104 cm2/V s

Bloch gain for terahertz radiation in semiconductor superlattices of different miniband widths mediated by acoustic and optical phonons

We report a study of the role of electron scattering at acoustic and polar optic phonons for Bloch gain of a terahertz radiation in semiconductor superlattices of different miniband widths. A three-dimensional Monte Carlo method was employed to calculate the dynamic mobility of miniband electrons in GaAs/AlAs superlattices subject to both static and high-frequency fields at low temperature (4 K); Bloch gain is indicated by a negative real part of the dynamic mobility. We found that for a superlattice with a miniband width smaller than the optic phonon energy (36 meV), scattering of electrons at acoustic phonons alone mediates the formation of electron bunches in momentum space and introduces gain, while for larger miniband widths, optic phonon scattering is dominant for gain. Due to a decrease of the energy-relaxation time of the miniband electrons, the alteration of the superlattice miniband width from smaller to larger magnitude, with respect to the optic phonon energy, results in broadening of the resonancelike dynamic mobility curve and considerable extension of the frequency range for the strong Bloch gain. The study delivers criteria for the observation of the Bloch gain

Amplification of a terahertz field in a semiconductor superlattice via phase-locked-k-space bunches of Bloch oscillating electrons

Applying a Monte Carlo technique for the simulation of the dynamics of electrons in a semiconductor superlattice, we studied the action of a terahertz field on the motion of electrons by performing Bloch oscillations subject to inelastic scattering. We found that, due to polar optic phonon emission, the Bloch oscillating electrons can form k-space bunches phase locked to the terahertz field. For frequencies smaller than the Bloch frequency, this gives rise to the amplification of the terahertz field. Our study may contribute to the development of a Bloch laser for terahertz radiation