A. A. Zhukov

Low-temperature conductance of the weak junction in InAs nanowire in the field of AFM scanning gate

We have investigated the conductance of an InAs nanowire in the presence of an electrical potential created by an AFM scanning gate at liquid helium temperature. The influence of the direction of a local electrical field on the tunneling rate through a weak junction in the InAs wire is clearly observed. To explain this behavior, the redistribution of the electrons among conductive channels in the wire must be taken into account. We have confirmed that the pattern of Coulomb blockade diamonds gives the same result for the ratio of quantum dot sizes as that revealed by scanning gate imaging.

Suppression of 2D superconductivity by the magnetic field: Quantum corrections vs. The superconductor-insulator transition

Magnetotransport of superconducting Nd2−xCexCuO4+y(NdCeCuO) films is studied in the temperature interval 0.3–30 K. The microscopic theory of the quantum corrections to conductivity, both in the Cooper and in the diffusion channels, qualitatively describes the main features of the experiment, including the negative magnetoresistance in the high-field limit. Comparison with the model of the field-induced superconductor-insulator transition is included and a crossover between these two theoretical approaches is discussed.Magnetotransport of superconducting Nd_{2-x}Ce_xCuO_{4+y} (NdCeCuO) films is studied in the temperature interval 0.3-30 K. The microscopic theory of the quantum corrections to conductivity, both in the Cooper and in the diffusion channels, qualitatively describes the main features of the experiment including the negative magnetoresistance in the high field limit. Comparison with the model of the field-induced superconductor-insulator transition (SIT) is included and a crossover between these two theoretical approaches is discussed.

Characteristic features of the temperature dependence of the surface impedance of YBa2Cu3O6.95 single crystals

The real and imaginary parts of the surface impedance Zs=Rs+iXs of YBa2Cu3O6.95 single crystals are measured at a frequency ω/π=9.4 GHz. The quantities Rs(T) and Xs(T) are linear functions of temperature for T<0.3Tc (Tc=93.5 K). A maximum of Rs(T) and a plateau of Xs(T) are observed in the interval 35<T<65 K. Our experimental data, just as all recent measurements of Rs(T) in YBa2Cu3O6.95 single crystals in the temperature range 0<T<1.3Tc, are described well in a two-fluid model which assumes electron-phonon scattering of quasiparticles.

Dependence of transport through carbon nanotubes on local Coulomb potential.

In this paper, we present the results of helium temperature transport measurements through carbon nanotubes using an AFM conductive tip as a mobile gate for creation of a local distributive Coulomb potential. In semiconducting nanotubes we observe shifting of the conductance peaks with changing of the AFM tip position. This result can be explained with a particle in the box quantum model. In high quality metallic nanotubes we observe that the local Coulomb potential does not destroy the fourfold degeneracy of the energy levels.

c-axis penetration depth in Bi2Sr2CaCu2O8+δ single crystals measured by ac-susceptibility and cavity perturbation technique

The c-axis penetration depth Δλc in Bi2Sr2CaCu2O8+δ (BSCCO) single crystals as a function of temperature has been determined using two techniques, namely, measurements of the ac-susceptibility at a frequency of 100 kHz and the surface impedance at 9.4 GHz. Both techniques yield an almost linear function Δλc(T)∝T in the temperature range T<0.5Tc. Electrodynamic analysis of the impedance anisotropy has allowed us to estimate λc(0)≈50 µm in BSCCO crystals overdoped with oxygen (Tc≈84 K) and λc(0)≈150 µm at the optimal doping level (Tc≈90 K).

Linear low-temperature dependence of the surface impedance of a Ba0.6K0.4BiO3 single crystal

The temperature dependences of the real part Rs and the imaginary part Xs of the surface impedance Zs=Rs+iXs of the superconductor Ba0.6K0.4BiO3 (Tc≃30 K) are measured at a frequency of 9.4 GHz. Its temperature dependence Zs(T) and that of the complex conductivity σs(T) can be described on the basis of a two-fluid model under two assumptions: The density of superconducting carriers increases linearly, and the relaxation time increases as a power law (∝1/T5), with decreasing temperature T<Tc. This model also describes well the curves Zs(T) and σs (T) recently measured for YBa2Cu3O6.95 and Bi2Sr2CaCu2O8 single crystals.

Measurements of work function of pristine and CuI doped carbon nanotubes

We report the results on measurements of the work function of carbon nanotubes and carbon-nanotube-based materials including pristine multi-walled and single-walled carbon nanotubes as well as single-walled carbon nanotubes intercalated by CuI with the Kelvin probe technique. We found the work function value 4.97–4.98 eV for pristine carbon nanotubes, while carbon nanotubes infilled with CuI demonstrate the work function value decreased by more than 0.1 eV (4.86–4.96 eV).

The electronic transport of top subband and disordered sea in an InAs nanowire in the presence of a mobile gate

We performed measurements at helium temperatures of the electronic transport in an InAs quantum wire (R(wire) ∼ 30 kΩ) in the presence of a charged tip of an atomic force microscope serving as a mobile gate. The period and the amplitude of the observed quasi-periodic oscillations are investigated in detail as a function of electron concentration in the linear and non-linear regime. We demonstrate the influence of the tip-to-sample distance on the ability to locally affect the top subband electrons as well as the electrons in the disordered sea. Furthermore, we introduce a new method of detection of the subband occupation in an InAs wire, which allows us to evaluate the number of electrons in the conductive band of the wire.

Investigations of local electronic transport in InAs nanowires by scanning gate microscopy at liquid helium temperatures

A set of experiments dedicated to investigations of local electronic transport in undoped InAs nanowires at liquid helium temperatures in the presence of a charged atomic-force microscope tip has been presented. Both nanowires without defects and with internal tunneling barriers were studied. The measurements were performed at various carrier concentrations in the systems and opacity of contact-to-wire interfaces. The regime of Coulomb blockade is investigated in detail including negative differential conductivity of the whole system. The situation with open contacts with one tunneling barrier and undivided wire is also addressed. Special attention is devoted to recently observed quasi-periodic standing waves.

Distortions of the coulomb blockade conductance line in scanning gate measurements of inas nanowire based quantum dots

We performed measurements at helium temperatures of the electronic transport in the linear regime in an InAs quantum wire in the presence of a charged tip of an atomic force microscope (AFM) at low electron concentration. We show that at certain concentration of electrons, only two closely placed quantum dots, both in the Coulomb blockade regime, govern conductance of the whole wire. Under this condition, two types of peculiarities—wobbling and splitting—arise in the behavior of the lines of the conductance peaks of Coulomb blockade. These peculiarities are measured in quantum-wire-based structures for the first time. We explain both peculiarities as an interplay of the conductance of two quantum dots present in the wire. Detailed modeling of wobbling behavior made in the framework of the orthodox theory of Coulomb blockade demonstrates good agreement with the obtained experimental data.