V. A. Berezovets

Inverse magnetoresistance in (FeCoB)-(Al2O3) magnetic granular composites

The magnetoresistance, magnetization, and microstructure of granular composites with the general formula (Fe40Co40B20)x(Al2O3)100−x were studied for contents of the amorphous metallic component both above and below the percolation threshold (x≈43). The low-temperature transverse magnetoresistance of the composites is negative at x=41 and practically zero for x=49. For metal contents below the percolation threshold (x=31), a noticeable (7–8%) positive magnetoresistance, reached in magnetic fields of about 17 kOe, was observed. Possible mechanisms of the generation of inverse (positive) magnetoresistance are discussed.

Energy spectrum and quantum magnetotransport in type-II heterojunctions

Specific features of the energy spectrum of a separated type-II heterojunction in an external magnetic field are studied theoretically and experimentally. It is shown that, due to hybridization of the states of the valence band of one semiconductor and the conduction band of the other semiconductor at the heterointerface, there are level anticrossings, which produce quasigaps in the density of states in a nonzero magnetic field. The experimental results of magnetotransport studies for the GaInAsSb/p-InAs quaternary solid solutions with different doping levels are shown to agree well with the results of simulation, and specific features of the energy spectrum of separated type-II heterojunctions are established.

Weak localization with a specific role of t symmetry (2D and 3D holes in tellurium)

The anomalous magnetoresistance in crystalline tellurium is analyzed for different p-type carrier dimensions: a bulk sample, size-quantized accumulation layers on different tellurium crystallographic surfaces, and tellurium clusters (tellurium embedded in a dielectric opal matrix). It is shown that the effect can be interpreted in all cases in terms of the theory of weak localization of noninteracting particles with inclusion of the specific features of the tellurium band spectrum, namely, fully lifted spin degeneracy, trigonal spectrum distortion, and a specific role played by the t symmetry in inter-valley scattering. The differences observed among the various manifestations of the weak localization effect are determined by the hole wave function phase-relaxation channel which is dominant in a particular case. A case is discussed where the time characterizing the inter-valley transition probability becomes comparable to the momentum relaxation time.

Electrical properties of tellurium clusters on the void sublattice of an opal crystal: The important role played by the Te-SiO2 interface

The temperature dependences of electrical resistivity and of the Hall effect of nanocluster tellurium crystals obtained by filling the voids in a dielectric (opal) matrix with a melt of pure and doped Te were studied. The Hall hole concentration peff was found to increase anomalously (by more than two orders of magnitude) in a sample prepared from pure Te and cooled to helium temperatures. At T=1.45 K, the hole concentration in this sample was peff≅6×1017 cm−3. At the same time, the Hall effect in this sample was observed to reverse sign at T≅200 K from positive for T<200 K to negative at higher temperatures. This implies a low impurity concentration (NA is less than at least 1015 cm−3). A nanocluster crystal of doped Te does not exhibit this anomaly; here, we have peff≅6×1017 cm−3 throughout the temperature region covered, as in the original Te. These features are assigned to the formation of a two-dimensional conducting accumulation layer near the Te-amorphous SiO2 (the opal material) interface at low temperatures; such a layer determines the low-temperature properties of nanocluster crystals prepared from pure Te. Actually, we obtained a model of a three-dimensional structure formed from a two-dimensional film.

Quantum corrections to 2D hole conductivity in a quantum well on \((10\bar 10)\)

AbstractThe anomalous positive magnetoresistance of a two-dimensional (2D) layer on Te

Specific features in the magnetoresistance oscillation spectrum from the two-dimensional accumulation layer on \((10\overline 1 0)\) surface

(10\bar 10)

Inverse magnetoresistance in (FeCoB)-(Al 2 O 3 ) magnetic granular composites

is analyzed, and it is shown that this phenomenon can be described within the weak localization theory taking into account the specific features of the band spectrum symmetry of a 2D layer on this tellurium surface and the associated peculiarities in the phase relaxation processes, as well as the existence of several 2D subbands. The main parameters of the theory have been determined, and it has been found that this orientation of the 2D layer is characterized by an extremely high probability of intersubband transitions in elastic scattering, which makes this case qualitatively different from the 2D hole system on the (0001) surface studied previously. The phenomenon is attributed to the difference in the character of electronic states between these crystal interfaces, namely, dangling covalent bonds in the chains making up the tellurium crystal on the (0001) surface, and the disruption of the weaker interchain Van der Waals bonds on the