Surface versus bulk state in topological insulator Bi2Se3 under environmental disorder

Abstract

Abstract:Topological insulators (TIs) are predicted to be composed of an insulating bulk state along with conducting channels on the boundary of the material. In Bi 2 Se 3 , however, the Fermi level naturally resides in the conduction band due to intrinsic doping by selenium vacancies, leading to metallic bulk states. In such non-ideal TIs it is not well understood how the surface and bulk states behave under environmental disorder. In this letter, based on transport measurements of Bi 2 Se 3 thin films, we show that the bulk states are sensitive to environmental disorder but the surface states remain robust.

Transport properties of topological insulators: Band bending, bulk metal-to-insulator transition, and weak anti-localization

“…What can be seen from Fig. 4 is that if the crystals start with upward band bending and low carrier densities on the surface and in the bulk, then as time increases the band bending flattens out, and upward band bending will eventually give way to downward bending; such an effect has been linked to charge doping by water vapor in atmospheric gases [24,[39][40][41]. This change of band bending character will be accompanied with the development of quantum well states on the surfaces, which are in parallel with the TSS.…”

Time-resolved terahertz dynamics in thin films of the topological insulator Bi2Se3

“…One reason is the chemical potential shift into the conduction band due to electron doping, typically by Se vacancies and anti-site defects. [11] Another effect interfering with ideal TI response occurs when the bulk bands cross the Fermi level near the material surface (band bending) and generate two dimensional electron gas (2DEG). This 2DEG is confined within ∼20 nm from the surface [12,13] and coexists with the topological surface states.…”

Stability of low-carrier-density topological-insulator Bi2Se3 thin films and effect of capping layers

“…Due to the initial high carrier densities, the carrier densities remain relatively stable in air with the change in carrier densities limited only to a few tens of percent. 7,12 The relative stability of these high-carrier-density samples has helped attaining numerous consistent results across different probing techniques even without any special care to protect the surface layers. 9,13 In contrast, recently developed low-carrier-density bulk-insulating Bi 2 Se 3 films 14,15 exhibit quite significant aging effect in air.…”

“…There have been transport and spectroscopic studies on how the properties of Bi 2 Se 3 evolve when it is exposed to atmospheric gases. [6][7][8] In regular Bi 2 Se 3 thin films grown on different substrates including sapphire, 9 silicon, 10 and amorphous silicon oxide, 11 the surface Fermi level generally resides above the bottom of bulk conduction band and their sheet carrier densities are generally much higher than ∼1 × 10 13 cm −2 with the bulk state of the samples metallic. Due to the initial high carrier densities, the carrier densities remain relatively stable in air with the change in carrier densities limited only to a few tens of percent.…”

“…Similar short-time decrease in carrier density was observed in our previous study of high-carrier-density Bi 2 Se 3 samples. 7 The trigger point of this decrease depends on ambient conditions, such as relative humidity and temperature. This shows that there are competing processes such that there is a short-time window in which the sample properties improve, and after that, it gets worse rapidly until the carrier density reaches twice the initial value after a day.…”