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Register a new userPlanar Hall effect from the surface of topological insulators
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A prominent feature of topological insulators (TIs) is the surface states comprising of spin-nondegenerate massless Dirac fermions. Recent technical advances have made it possible to address the surface transport properties of TI thin films while tuning the Fermi levels of both top and bottom surfaces across the Dirac point by electrostatic gating. This opened the window for studying the spin-nondegenerate Dirac physics peculiar to TIs. Here we report our discovery of a novel planar Hall effect (PHE) from the TI surface, which results from a hitherto-unknown resistivity anisotropy induced by an in-plane magnetic field. This effect is observed in dual-gated devices of bulk-insulating Bi$_{2-x}$Sb$_{x}$Te$_{3}$ thin films, in which both top and bottom surfaces are gated. The origin of PHE is the peculiar time-reversal-breaking effect of an in-plane magnetic field, which anisotropically lifts the protection of surface Dirac fermions from back-scattering. The key signature of the field-induced anisotropy is a strong dependence on the gate voltage with a characteristic two-peak structure near the Dirac point which is explained theoretically using a self-consistent T-matrix approximation. The observed PHE provides a new tool to analyze and manipulate the topological protection of the TI surface in future experiments.
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Whether the surface states in SmB6 are topological is still a critical issue in the field of topological Kondo insulators. In the magneto-transport study of single crystalline SmB6 microribbons, we have revealed a positive planar Hall effect (PHE), the amplitude of which increases dramatically with decreasing temperatures but saturates below 5 K. This positive PHE is ascribed to the surface states of SmB6 and expected to arise from the anisotropy in lifting the topological protection from back-scattering by the in-plane magnetic field, thus suggesting the topological nature of surface states in SmB6. On the contrary, a negative PHE is observed for the bulk states at high temperatures, which is almost three orders of magnitudes weaker than the surface-induced positive PHE.
The Hall effect, the anomalous Hall effect and the spin Hall effect are fundamental transport processes in solids arising from the Lorentz force and the spin-orbit coupling respectively. The quant
We report a proximity-driven large anomalous Hall effect in all-telluride heterostructures consisting of ferromagnetic insulator Cr2Ge2Te6 and topological insulator (Bi,Sb)2Te3. Despite small magnetization in the (Bi,Sb)2Te3 layer, the anomalous Hall conductivity reaches a large value of 0.2e2/h in accord with a ferromagnetic response of the Cr2Ge2Te6. The results show that the exchange coupling between the surface state of the topological insulator and the proximitized Cr2Ge2Te6 layer is effective and strong enough to open the sizable exchange gap in the surface state.
Negative longitudinal magnetoresistance, in the presence of an external magnetic field parallel to the direction of an applied current, has recently been experimentally verified in Weyl semimetals and topological insulators in the bulk conduction limit. The appearance of negative longitudinal magnetoresistance in topological semimetals is understood as an effect of chiral anomaly, whereas it is not well-defined in topological insulators. Another intriguing phenomenon, planar Hall effect - appearance of a transverse voltage in the plane of applied co-planar electric and magnetic fields not perfectly aligned to each other, a configuration in which the conventional Hall effect vanishes, has recently been suggested to exist in Weyl semimetals. In this paper we present a quasi-classical theory of planar Hall effect of a three-dimensional topological insulator in the bulk conduction limit. Starting from Boltzmann transport equations we derive the expressions for planar Hall conductivity and longitudinal magnetoconductivity in topological insulators and show the important roles played by the orbital magnetic moment for the appearance of planar Hall effect. Our theoretical results predict specific experimental signatures for topological insulators that can be directly checked in experiments.
We report transport studies on a three dimensional, 70 nm thick HgTe layer, which is strained by epitaxial growth on a CdTe substrate. The strain induces a band gap in the otherwise semi-metallic HgTe, which thus becomes a three dimensional topological insulator. Contributions from residual bulk carriers to the transport properties of the gapped HgTe layer are negligible at mK temperatures. As a result, the sample exhibits a quantized Hall effect that results from the 2D single cone Dirac-like topological surface states.
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