We present a study of low temperature electron transport (resistivity, magnetoresistance and Hall coefficient) in SmB6 single crystals having different polar (100) and nonpolar (110) and (111) surfaces after mechanical polishing and chemical etching. The estimation of effective parameters for surface and bulk charge carriers allows us to conclude that surface conductivity is very sensitive to the method of surface treatment. The most pronounced change is observed for the polar (100) surface, for which the related Hall concentration of charge carriers at 2 K decreases more than by 2 orders of magnitude and the Hall mobility increases by a factor of 15 after etching these faces in diluted nitric acid. We suggest that the strong dependence of surface properties on the type of treatment may result from both topological protection, which is influenced by intrinsic defects or surface reconstruction, and band bending effects, which modulate the properties of the surface conduction layer in case of polar faces.

The galvanomagnetic characteristics of SmB6 single crystals are studied within the temperature range of 1.9‒3.6 K at different orientations of the crystal faces. As a result, the electrical resistivities of the surfaces corresponding to the (100), (110), (111), and (211) crystallographic planes are determined. It is shown that the effective parameters of charge carriers, which determine the surface conductivity in SmB6, depend both on the orientation of the surface and on the method of its processing. It is found that the etching of polished polar surfaces formed by (100) planes leads at 1.9 K to a decrease in the density and to an increase in the mobility of surface n-type charge carriers from 113/a2 and 1.12 cm2/(V s) to 0.76/a2 and 18 cm2/(V s), respectively (lattice parameter a ≈ 4.134 Å). For etched nonpolar surfaces corresponding to the (110) and (111) planes, the maximum density of surface charge carriers (per unit area of the surface Brillouin zone) is found to increase by factors of 2.3 and 3.9, respectively. It is proposed to use this parameter as a simple criterion to identify the features of electron transport due to the nontrivial topology of the band structure of SmB6.

We present the results of experimental studies on the synthesis by molecular-beam epitaxy of AlGaAs nanowires with InAs quantum dots. The morphological, structural, and optical properties of the grown nanostructures have been studied. It is important to note that the emission from quantum dots is observed in the wavelength range from 750 to 970 nm. Assumptions about the nature of short-wavelength emission from quantum dots are formulated. In particular, one of the reasons may be a significant desorption of indium atoms and the presence of gallium atoms in catalyst drops during the growth at a substrate temperature of 510◦C. The proposed technology opens up new possibilities for integration direct-gap III−V materials with a silicon platform for various applications in photonics and quantum communications.

Seebeck effect in the crystalline samples of Eu

Seebeck effect in the crystalline samples of EuxYb1-xB6(x= 0, 0.082, 0.127, 0.9, 1) was investigated at temperatures 2-300 K. For all the compounds thermopower is shown to be well described by the sum of diffusion (S-d=AT) and phonon drag components. The latter contribution is induced by quasilocal (Einstein) modes of ytterbium and europium ions with characteristic temperatures Theta(E)(YbB6) approximate to 91 K and Theta(E)(EuB6) approximate to 122 K. The estimation of effective massm*of the charge carriers proves that increasing of Eu content induces crossover from 'heavy' holes withm(h)*(x <= 0.127) approximate to 0.3-0.36m(0)to 'light' electrons withm(e)*(x > 0.9) approximate to 0.12-0.13m(0)(m(0)-free electron mass). For the Eu-rich compounds we propose the existence of additional point on the phase diagram, which corresponds to short-range magnetic order with enhanced spin fluctuations preceding the stabilization of magnetic polarons.