THESIS
2014
xvi, 79 pages : color illustrations ; 30 cm
Abstract
The electrical transport properties of topological insulators Bi
2Te
3, Bi
2Se
3 and related specific structures have been investigated in this thesis. Three topics of topological insulators are systematically studied, including the electron-electron interaction in antidot nanostructured Bi
2Te
3 thin films, the interface effect of Nb-Bi
2Te
3 hybrid structure and the anisotropy transport properties of high-index Bi
2Se
3 (221) thin films.
Recently, a logarithmic decrease of conductivity has been observed in topological insulators at low temperatures, implying a tendency of localization of surface electrons, and is attributed to electron-electron interaction. By introducing different antidots nanostructure in Bi
2Te
3 thin films, we studied the Altshuler-Aronov effect on topological insulator Bi
2T...[
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The electrical transport properties of topological insulators Bi
2Te
3, Bi
2Se
3 and related specific structures have been investigated in this thesis. Three topics of topological insulators are systematically studied, including the electron-electron interaction in antidot nanostructured Bi
2Te
3 thin films, the interface effect of Nb-Bi
2Te
3 hybrid structure and the anisotropy transport properties of high-index Bi
2Se
3 (221) thin films.
Recently, a logarithmic decrease of conductivity has been observed in topological insulators at low temperatures, implying a tendency of localization of surface electrons, and is attributed to electron-electron interaction. By introducing different antidots nanostructure in Bi
2Te
3 thin films, we studied the Altshuler-Aronov effect on topological insulator Bi
2Te
3. A systematic change of the conductivity-lnT slope with the antidot density is observed, which indicates the achievement of tuning the electron-electron interaction in disorder topological insulator system. Meanwhile, the magnetoresistance measurements manifest that the weak antilocalization effect weakens and the electron-electron interaction becomes a dominant decoherence mechanism as the antidot density increases. This also provides additional evidence for the success in tuning the electron-electron interaction. A possible explanation based on the Dirac Fermions theory is further tentatively provided, which implies antidot nanostructure will change the dielectric constant of the sample and finally affect the electron-electron interaction.
Superconductor and topological insulator hybrid structures attract lots of attention due to the possibility for the detection of Majorana Fermions. In our Nb-Bi
2Te
3 hybrid structures, transport measurements show that an upturn of the resistance occurs below the Nb superconducting transition temperature. Meanwhile, a differential resistance central peak and a negative magnetoresistance are observed. The resistance upturn, differential resistance peak, and negative magnetoresistance can be suppressed by increasing measurement current, temperature, and applied magnetic field. These phenomena are explained in terms of an energy barrier effect induced by the Nb superconducting gap and the suppression of Andreev reflection due to the low transparency at the Nb-Bi
2Te
3 interface.
Bi
2Se
3 thin films are normally grown along its c-axis and previous transport measurements are mainly obtained from the (111) surface of topological insulators. We studied the transport properties of high-index Bi
2Se
3 (221) thin films. Hall measurements demonstrate a non-linear magnetic field dependent resistance at high temperatures and two-band model fitting reveals the existence of the multiband conduction. The magnetoresistance studies show a quasi-2D linear magnetoresistance at high temperature region, which is probably caused by surface accumulation layer and is different from others’ works observed in topological insulator which are attributed to the gapless linear energy dispersion. In addition, an abnormal negative magneto-resistance that shows a non-monotonic temperature dependence and persists even at high temperatures and in strong magnetic fields, is also observed.
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