We study experimentally the transport properties of "inverted" semiconductor HgT e-based quantum well, which is related to the two-dimensional topological insulator, in diffusive transport regime. We perform nonlocal electrical measurements in the absence of the magnetic field and observe large signal due to the edge states. It demonstrates, that the edge states can propagate over long distance ∼ 1mm, and, therefore, there is no difference between local and non local electrical measurements in topological insulator. In the presence of the in-plane magnetic field we find strong decrease of the local resistance and complete suppression of the nonlocal resistance. We attribute this observation to the transition between topological insulator and bulk metal induced by the in-plane magnetic field. Recently, a novel class of the topological state of a quantum matter has emerged, called topological insulator [1][2][3][4]. The first famous example of the two dimensional topological insulator (2DTI) is the integer quantum Hall effect (QHE) state on the resistance minima [5]. Such system represents the 2D electron gas in the presence of the strong perpendicular magnetic field, when all current is carried by the edge states, while electrons in the bulk region are localized. The number of the edge states are determined by the Landau level filling factor ν. The edge states are unidirectional because of the breaking of the time-reversal (TR) symmetry due to the magnetic field and robust against impurity scattering. Note, that disorder plays the crucial role in establishment of the Hall plateau in the finite region of the magnetic field or electron density.Another class of 2DTI is the quantum spin Hall effect state, which can be realized in 2D system with strong spin-orbit interaction in the absence of the magnetic field [1][2][3][4]. It has been shown that an "inverted" semiconductor HgTeCdTe quantum well [2,4], possess the insulating phase having the gap in the bulk electron spectrum and a single pair of counterpropagating or helical edge states for the two opposite spin polarizations. Remarkable consequence of the presence of the edge states in ballistic 2DTI is a quantized longitudinal resistance R = h/2e 2 , which has been observed in micrometer scale Hall bars [4]. The edge states are expected to be insensitive to weak, nonmagnetic impurity scattering due to destructive interference between two backscattering paths of the helical edge states ( see review [6]). It is worth noting that the backscattering does not destroy the edge states, therefore any 2DTI sample represents almost ideal natural one dimensional (1D) wire localized near the sample edge.In this letter we present an experimental study of the transport properties of "inverted" HgT e-based quantum well which possesses a pair of counter-propagating or helical edge states strongly mixed by spin flip scattering. When the Fermi level passes the bulk insulating gap, the devices revel unusual behaviour, which is characterized by high resistance R >> h/e 2 with metallic...

Our experimental studies of electron transport in wide (14 nm) HgTe quantum wells confirm the persistence of a two-dimensional topological insulator state reported previously for narrower wells, where it was justified theoretically. Comparison of local and nonlocal resistance measurements indicate edge state transport in the samples of about 1 mm size at temperatures below 1 K. Temperature dependence of the resistances suggests an insulating gap of the order of a few meV. In samples with sizes smaller than 10  μm a quasiballistic transport via the edge states is observed.

No abstract