Manifestation of Topological Protection in Transport Properties of EpitaxialBi2Se3Thin Films

Abstract

The massless Dirac fermions residing on the surface of three-dimensional topological insulators are protected from backscattering and cannot be localized by disorder, but such protection can be lifted in ultrathin films when the three-dimensionality is lost. By measuring the Shubnikov-de Haas oscillations in a series of high-quality Bi2Se3 thin films, we revealed a systematic evolution of the surface conductance as a function of thickness and found a striking manifestation of the topological protection: The metallic surface transport abruptly diminishes below the critical thickness of ~6 nm, at which an energy gap opens in the surface state and the Dirac fermions become massive. At the same time, the weak antilocalization behavior is found to weaken in the gapped phase due to the loss of π Berry phase.

Magneto-transport behaviour of Bi2Se3−xTex: role of disorder

“…The decrease in the mean free path (l e ) makes it conducive for the condition l  > l e (l  : phase coherence length ) to be met leading to the quantum corrections to the transport, viz., the WAL behaviour that points to the involvement of topological surface state in the transport behaviour [12]. With the increase of magnetic field, this WAL feature is seen to transform to the WL behaviour -as has been observed in other experiments [18,24]. As seen in figure 6, the change from WAL to WL occurs when the Hall resistance shows a non-linear behaviour, that requires analysis in terms of two carrier transport involving both the surface and bulk electrons [19].…”

“…It has been shown from earlier studies [19,20] that the cusp like positive magneto-resistance behaviour attributed to WAL gives way to negative magneto-resistance on account of opening of band gap at the Dirac point due to magnetic impurity [21], or due to hybridisation of the bottom and top surface states in very thin samples [18,22]. As our sample is neither thin film nor has any magnetic impurities, we could rule out such interpretation of the WAL-WL crossover.…”

Scanning tunneling microscopy of gate tunable topological insulator Bi2Se3thin films

“…Figure 2(d) shows the STM topography of a nominal 3QL thick film with flat terraces and 1 nm step heights, corresponding to one QL. Figure 3(a) shows the two-terminal resistance measured during sample cool-down, which displays an insulating behavior with resistance increasing about two orders of magnitude between room temperature and 5 K. Similar insulating behavior has always been seen in ultrathin Bi 2 Se 3 films, which could be due to strong interactions [25], or Anderson localization [26,27]. To test the gating ability of the TI/STO device, we measured the 2-terminal resistance through the 3QL film vs. gate voltage (Fig.…”

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

“…In thin-film samples of Bi 2 Se 3 à is not the ideal value of 2, but rather close to half of this at à ≈ 1 [27,[44][45][46][47][48]] (see Fig. 7).…”