Topological delocalization and tuning of surface channel separation in Bi2Se2Te Topological Insulator Thin films

Abstract

The surface states of a 3D topological insulator (TI) exhibit topological protection against backscattering. However, the contribution of bulk electrons to the transport data is an impediment to the topological protection of surface states. We report the tuning of the chemical potential in the bulk in Bi2Se2Te TI thin films, pinning it near the center of the bulk band gap, thereby suppressing the bulk carriers. The temperature dependent resistance of these films show activated behavior down to 50 K, followed by a metallic transition at lower temperatures, a hallmark of robustness of TI surface states. Manifestation of topological protection and surface dominated transport is explained by 2D weak antilocalization phenomenon. We further explore the effect of surface to bulk coupling in TI in this work, which is captured by the number of effective conducting surface channels that participate in the transport. The presence of a single conducting channel indicates a strong surface to bulk coupling which is detrimental to purely topological transport. We demonstrate the decoupling of topological surface states on opposite surfaces of thin films, thereby suppressing the bulk transport. Our findings provide a deeper understanding of surface to bulk coupling along with topological transport behavior and their respective tunability.

Weak Antilocalization and Quantum Oscillations of Surface States in Topologically Nontrivial DyPdBi(110)Half Heusler alloy

“…Fitting parameters obtained from the resistance Vs temperature data indicate that below 25 K e-e scattering dominates the resistivity behavior. This is possibly arising from either the presence of disorder on the surface of TI leading to e-e correlation among surface states or due to freezing of bulk carriers in the impurity bands 52 . Above 25 K, evidently the resistivity behavior can be explained by e-ph scattering and ph -drag effects govern the resistivity behavior.…”

Modeling of magneto-conductivity of bismuth selenide: a topological insulator

“…The HLN is fitted and found to be applicable at a low magnetic field only, (≈1 T) [22,[24][25][26], whereas it deviates from experimental data at a higher field. A quadratic term consisting of quantum and classical contributions is added in conventional HLN [27][28][29], which accounts for the MC in the entire field range. It is suggested that the contribution of bulk carrier starts to dominate above around 100 K. However, we find that these quadratic term does not appropriately account for the MC in our case as apart from these quantum scatterings, there is a possible role of bulk carriers that comes into the picture at higher temperatures and applied magnetic fields.…”

“…The HLN is fitted and found to be applicable at a low magnetic field only, (≈1 Tesla) [23,[25][26][27], whereas it deviates from experimental data at a higher field. A quadratic term consisting of quantum and classical contributions is added in conventional HLN [28][29][30], which accounts for the MC in the entire field range. It is suggested that the contribution of bulk carrier starts to dominate above around 100K.…”

Surface-bulk coupling in a Bi2Te3 nanoplate grown by van der Waals epitaxy

“…, a measure of the strength of the surface-bulk state coupling (with τ φ / τ SB > 1 referring to the surface-bulk-coherently-coupled case and τ φ / τ SB < 1 referring to the case where the surface and bulk states are no longer coherently coupled). 15,19…”

“…Previously, it was shown that the ratio of τ φ / τ SB can be used to characterize the effect of the surface-bulk state coupling. 15,19 When τ φ / τ SB > 1, electrons maintain phase coherence during transfer from one 2D conduction channel to the other 2D channel, leading to the formation of a two-channel-coherently-coupled conduction channel, and the system is described as a strong inter-channel coupling case. However, when τ φ / τ SB < 1, electrons will lose phase coherence before being scattered into the other channel and electrons in the two conduction channels are no longer coherently coupled.…”