Abstract
Two-dimensional (2D) topological surface states in a three-dimensional topological insulator (TI) should produce uniform 2D surface current distribution. However, our transport current imaging studies on Bi2Se3 thin film reveal non-uniform current sheet flow at 15 K with strong edge current flow. This is consistent with other imaging studies on thin films of Bi2Se3. In contrast to strong edge current flow in thin films, in single crystal of Bi2Se3 at 15 K our current imaging studies show the presence of 3.6 nm thick uniform 2D sheet current flow. Above 70 K, this uniform 2D sheet current sheet begins to disintegrate into a spatially non-uniform flow. The flow becomes patchy with regions having high and low current density. The area fraction of the patches with high current density rapidly decreases at temperatures above 70 K, with a temperature dependence of the form 1/left| {T - 70} right|^{0.35}. The temperature scale of 70 K coincides with the onset of bulk conductivity in the crystal due to electron doping by selenium vacancy clusters in Bi2Se3. Thus our results show a temperature dependent competition between surface and bulk conductivity produces a temperature dependent variation in uniformity of current flow in the topological insulator.
Highlights
Two-dimensional (2D) topological surface states in a three-dimensional topological insulator (TI) should produce uniform 2D surface current distribution
We use this current imaging technique to study the nature of surface and bulk current distribution TI thin film and single crystal
As the TI material gets electron doped via the Se vacancies, a conventional fluid of electrons appears in the material bulk at finite temperatures
Summary
Two-dimensional (2D) topological surface states in a three-dimensional topological insulator (TI) should produce uniform 2D surface current distribution. Motivated by the above issues, we image the current flow in a Bi2Se3 from 15 upto 290 K, using the high sensitivity magneto-optical self-field imaging technique We use this current imaging technique to study the nature of surface and bulk current distribution TI thin film and single crystal. In Bi2Se3 single crystal at low T we readily observe highly uniform topological 2D sheet current flow associated with 2D surface state in 3D TI. With increasing temperature above 70 K, the uniform 2D conducting sheet disintegrates into smaller patches with high and low current density (J) distribution Such imaging of uniform 2D sheet current flow in 3D TI single crystal and tracking its evolution as a function of temperature, to the best of our knowledge hasn’t been shown before. The temperature dependence of the high J area fraction above 70 K follows the form, 1 |T − 70|0.35
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