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NIKOLAEVA, Albina; KONOPKO, Leonid; ROGACKI, Krzysztof; HUBER, Tito; GHERGISHAN, Igor; BOTNARY, Oxana. Dirac states and thermoelectric properties, topological insulators bi2te3 wires and layers. In: Materials Science and Condensed Matter Physics. Ediția a 9-a, 25-28 septembrie 2018, Chișinău. Chișinău, Republica Moldova: Institutul de Fizică Aplicată, 2018, p. 212.
|Materials Science and Condensed Matter Physics
Ediția a 9-a, 2018
Conferința "International Conference on Materials Science and Condensed Matter Physics" |
Chișinău, Moldova, 25-28 septembrie 2018
In this paper, we present a study of Shubnikov de Haas (SdH) oscillations at 4.2 and 2.1 K and temperature dependences of thermopower α(T) and resistivity ρ(T) for layers and wires based on Bi2Te3 topological insulators (TIs) in a range of 4.2–300 K. Single-crystal Bi2Te3 layers of n- and p-type with a thickness of 10–30 μm were prepared by the mechanical exfoliation of layers from a bulk single-crystal ingot of a similar composition using a scotch tape. The mechanical exfoliation mostly results in breaking the Te(1) - Te(1) van der Waals bond and the formation of few-quintuples layers. The X-ray diffraction studies revealed that the layers had a single-crystal structure; the cleavage plane of the layers was perpendicular to the C3 trigonal axis. Glass-insulated Bi2Te3 microwires were prepared by the Ulitovsky–Taylor method ; in general, the microwire core had a polycristalline structure consisting of large disoriented single-crystal blocks. High quantum mobilities μg~2*104 cm2/V*s were determined from SdH oscillations in longitudinal (HïïI) and transverse (HￌI) magnetic fields of up to 14 T at 4.2–2.1 K; the mobilities are substantially higher than those in bulk Bi2Te3 samples of the same composition. A phase shift in SdH oscillations in longitudinal (HïïI) and transverse (HￌI) magnetic fields was found at H→ꝏ, which is characteristic of the Dirac state of TIs at the surface . Analysis of the experimental data on the temperature dependences of resistivity ρ(T) and thermopower α(T) in layers and wires of n- and p-type makes it possible to calculate the power factor P.f.= α2σ(T) . It was found that the power factor has a maximum value for n-type layers and p-type wires in a temperature range of about 300 K. Taking into account that heat conductivity χ in thin layers is essentially lower than that in the bulk Bi2Te3 samples, it is reasonable to expect a considerable increase in the thermoelectric efficiency (figure of merit) ZT=α2σ/χ*T. The results allow us to recommend the use of wires and layers of Bi2Te3 as two branches in micro – electro-thermal systems for thermoelectric applications.