Group members:

 

Main areas of research

 

●  Studying the flow of spin-polarized current in composites made of CrO2 half-metal nanoparticles.

 

● Determining electron transport characteristics of low-dimensional systems made of carbon nanotubes and graphite by studying quantum corrections to the resistance caused by Weak Localization (WL) and Electron-Electron Interaction (EEL) phenomena.

 

● Studying of Shubnikov-de Haas magneto-quantum oscillations and quantum interference effects in a two-dimensional gas of charge carriers (holes) in Si0.6Ge0.4/Si0.2Ge0.8/Si0.6Ge0.4 heterostructures.

 

● Studying of metal-insulator transitions in transition metal oxides.

 

 

Equipment

 

● Equipment for in situ studies of galvanomagnetic properties of quench-condensed thin metal films in magnetic fields up to 6 T in the temperature range 0.3 – 300 K Deep oil-free vacuum is provided by zeolite pumps, a magnetic discharge diode pump, and a high-vacuum pump of the «Orbitron» type.

 

● Revolving at an arbitrary angle Kapitsa’s-design solenoid with a cryostat for studies of galvanomagnetic anisotropy of single crystals. Magnetic field sweeping from   0.03 to 2 T with a smooth transition through zero in the temperature range from 4.2 to 450 K.

 

● Equipment for studies of galvanomagnetic and thermomagnetic properties of metal and semiconductor specimens of single crystals and films in the temperature range from 1.6 to 350 K with a steady or sweeping smoothly from – 2 T to + 2 T magnetic field.

 

● Equipment with superconducting solenoid for quantum oscillations measurements (magnetic fields up to 6 T  in  the temperature range 1.7 – 300 K). Simple compensation method and high selective deep modulation of magnetic field method are provided.

 

● Equipment for studying  single crystal samples conductivity and quantum oscillations under uniaxial compression (magnetic field up to 6 T in the temperature range 1.7 – 4.2 K).

 

● Equipment for studies of galvanomagnetic properties of samples in pulse magnetic field of 16 ms up to 20 T.

 

 

Important results in recent years

 

● The influence of the shape of CrO2 nanoparticles, as well as the thickness and material properties of intergranular dielectric layers (chromium oxide Cr2O3 or chromium oxyhydroxide β-CrOOH) on tunnel resistance and magnetoresistance (MR) of pressed powder samples was studied. Non-metallic temperature resistance behavior and giant negative tunnel MR were found for all samples at low temperatures. The maximum value of MR at T ≈ 5 K and a relatively small magnetic field (H = 0.5 T) is approximately 37%. With increasing temperature, MR rapidly decreased (to ≈1% at H = 1 T, T ≈ 200 K) [1].

 

● The temperature dependences of resistance and magnetoresistance of two ceramics samples RuSr2(Eu1.5Ce0.5)Cu2O10−δ were analyzed after their long-term storage (10 years) in an ambient atmosphere and losing most of their superstoichiometric and some of their stoichiometric oxygen. The issues of stability of the superconducting state in ruthenocuprates, as well as the peculiarities of interaction of various types of hopping conductivity and superconductivity in granular magnetic materials, have been clarified [2].

 

● Studies of the negative magnetoresistance of multilayer carbon nanotubes in the temperature range of 4.2 ÷ 200 K and magnetic fields up to 9 T have shown that for small magnetic fields and low temperatures, the dependence of conductivity on the magnetic field is quadratic. Further, as the magnetic field increases, the dependence becomes logarithmic, which can be described by models of weak localization and interaction of charge carriers. It is shown that the quantum correction to the conductivity due to the weak localization of charge carriers significantly exceeds the addition due to the effect of the charge carriers’ interaction. Within the framework of these models, using experimental data on the field and temperature dependence of magnetoresistance, the Fermi energy, the value of the charge carrier interaction constant, and the exact form of the temperature dependence of the phase relaxation time for the wave function of the charge carriers were estimated [3].

 

● Using the example of a pressed sample made of chromium dioxide nanoparticles covered with insulating shells, the connection between the electron transport subsystem and the magnetic subsystem in granular spin-polarized metals was studied. It is shown that the spin-polarized tunnel transport current can affect the characteristic fields of the coercive force for the percolation cluster, which is formed in the sample with decreasing temperature [4].

 

● Temperature and magnetic field dependences of the resistance of functionalized multiwalled carbon nanotubes (MWCNTs) were studied in the temperature range T = 4.2–200 K and magnetic fields up to B = 9 T. The contribution to conductivity of functionalized MWCNTs due to the weak localization effect exceeded the quantum correction due to the effect of charge carrier interaction for all temperatures and in the entire range of applied magnetic fields, with the exception of magnetic fields above B = 6.5 T at T = 5 K. Within the framework of weak localization and charge carriers’ interaction models, the Fermi energy was estimated, the explicit form of the temperature dependence of the phase relaxation time for the wave function was determined, and the charge carrier interaction constant was calculated at different temperatures. It is shown that the functionalization of MWCNTs leads to the weakening of the temperature dependence of phase relaxation time for the wave function and the shift of the Fermi energy toward the valence band compared to non-functionalized MWCNTs [5].

 

● Shubnkov-de-Haas magneto-quantum oscillations and quantum interference effects in a two-dimensional gas of charge carriers (holes) in Si0.6Ge0.4/Si0.2Ge0.8/Si0.6Ge0.4 heterostructures were studied. For samples of quantum wells with a width of 8 nm, 19.5 nm, and 25.6 nm the analysis of the dependences of the resistance on the magnetic field made it possible to calculate the kinetic characteristics of the charge carriers for the cases of one and two occupied subbands and to observe the transition from the diffusion mode of manifestation of quantum corrections, caused by the effect of weak hole localization, to the intermediate one. In all regimes, the behavior of quantum correction caused by the effect of the charge carriers' interaction agrees with theoretical predictions. The temperature dependence of the phonon-hole relaxation time was calculated [6].