Yu. A. Kolesnichenko

Structure and magnetic properties of multi-walled carbon nanotubes modified with iron

Magnetic properties of multi-walled carbon nanotubes modified with iron MWCNT+Fe are studied in detail in the temperature range 4.2–300 K. Carbon encapsulated Fe nanoparticles were produced by chemical vapor deposition. Low-temperature SQUID magnetization measurements are supplemented by structural studies employing thermogravimetric TG analysis, transmission electron microscopy TEM , x-ray diffraction spectroscopy XRD , and scanning electron microscopy SEM . The magnetic susceptibility of MWCNT+Fe was also studied above room temperature to provide a complete picture of its magnetic phase transitions.

Method to determine defect positions below a metal surface by STM

The oscillatory voltage dependence of the conductance of a quantum point contact in the presence of a single pointlike defect has been analyzed theoretically. Such signals are detectable and may be exploited to obtain information on defect positions below a metal surface. Both tunnel junctions and ballistic contacts of adiabatic shape have been considered. The effect of quantum interference has been taken into account between the principal wave that is directly transmitted through the contact and the partial wave that is scattered by the contact and the defect. This effect leads to oscillations of the conductance as a function of applied voltage. We obtain the dependence of the period and amplitude of the conductance oscillations on the position of the defect inside the metal.

Magnetoresistance of nanocarbon materials based on carbon nanotubes

The results of experimental investigations of magnetoresistance in nanocarbon material (NCM) containing carbon nanotubes in magnetic field up to 5 T and at temperature up to 0.54 K are reported. The obtained experimental magnetoresistance curves of NCM are described satisfactorily within the framework of the shrinkage effect of wave function of localized state in a magnetic field along with the spin-polarization mechanism.

Signature of Fermi-surface anisotropy in point contact conductance in the presence of defects

like, here we investigate the effects of Fermi surface anisotropy. We demonstrate that the amplitude and period of the conductance oscillations are determined by the local geometry of the Fermi surface. The signal results from those points for which the electron velocity is directed along the vector connecting the point contact to the defect. For a general Fermi surface geometry the position of the maximum amplitude of the conductance oscillations is not found for the tip directly above the defect. We have determined optimal conditions for determination of defect positions in metals with closed and open Fermi surfaces.

Spontaneous currents in Josephson junctions between unconventional superconductors and d-wave qubits. (Review)

The modern physics of superconductivity can be called the physics of unconventional superconductivity. The discovery of the d-wave symmetry of the order parameter in high-temperature superconductors and the triplet superconductivity in compound Sr2RuO4 has caused a huge stream of theoretical and experimental investigations of unconventional superconductors. In this review we discuss some novel aspects of the Josephson effect which are related to the symmetry of the order parameter. The most intriguing of them is spontaneous current generation in an unconventional weak link. The example of a Josephson junction in the form of a grain boundary between two disorientated d-wave or f-wave superconductors is considered in detail. Josephson current–phase relations and the phase dependences of the spontaneous current that flows along the interface are analyzed. The spontaneous current and spontaneous phase difference are manifestations of the time-reversal symmetry (T ) breaking states in the system. We analyzed t...

Josephson and spontaneous currents at the interface between two d-wave superconductors with transport current in the banks

A stationary Josephson effect in the ballistic contact of two d-wave superconductors with different orientation of the axes and with transport current in the banks is considered theoretically. The influence of the transport current on the current–phase relation of the Josephson and tangential currents at the interface is studied. It is demonstrated that the spontaneous surface current at the interface depends on the transport current in the banks due to the interference of the angle-dependent condensate wave functions of the two superconductors.

Magneto-quantum oscillations of the conductance of a tunnel point contact in the presence of a single defect

The influence of a strong magnetic field

Theory of oscillations in STM conductance caused by subsurface defects (Review Article)

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Conductance of a tunnel point contact of noble metals in the presence of a single defect

to the conductance of a tunnel point contact in the presence of a single defect has been considered. We demonstrate that the conductance exhibits specific magneto-quantum oscillations, the amplitude and period of which depend on the distance between the contact and the defect. We show that a nonmonotonic dependence of the point-contact conductance results from a superposition of two types of oscillations: A short period oscillation arising from the electrons being focused by the field

Nonlocal mixing of supercurrents in Josephson ballistic point contacts

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