![]() Moreover XRD analysis reveals the disordered occupation of Te/Se atoms in the quintuple layer unit unlike BTS which has ordered occupation of Te/Se atoms in its skippenite crystal structure and due to this fact it has highest possible bulk resistivity found in any topological insulator candidate till now. One can clearly see that the films grow along the c-axis. XRD pattern of a typical thin film is shown in Fig. To determine the chemical composition and crystalline nature of the thin films we performed Raman spectroscopy, EDX and X- ray diffraction (XRD) measurements. 23,26 A large spin texture promises a non-trivial Berry phase that restrains the backscattering. 28 Furthermore, it has been theoretically proposed that BST has a large spin texture with a Dirac point in the bulk band gap. 25–27 We were interested in the intermediate ternary compound BST since there has been limited study on it despite BST being predicted as an ideal candidate for intrinsic TI like its sister compound BTS. 24,25 We believe that an intrinsic TI state can be created by alloying two TI materials Bi 2Te 3 and Bi 2Se 3 to form either Bi 2Se 2Te (BST), Bi 2Te 2Se (BTS) or some intermediate ternary tetradymide alloys. Apart from gating, doping these alloys with Ca, Sb and Sn has proved to be useful in tuning the chemical potential in the bulk band gap but these doping in turn create defects, thereby rendering it impossible to realize an intrinsic TI. 2 It is possible to control the Fermi surface by gating thereby pushing it in the bulk band gap. In the second generation binary alloys there has always been a problem of unintentional doping which result in dominant bulk charge carriers which overwhelm the surface state conduction. 18,19 In addition to this, owing to the topologically protected surface states, these systems also open new platforms for device applications (low power spintronics) and quantum computing. 9,11,12,15–17 In recent times, intense research work has been carried out from a fundamental point of view both in theory as well as experiments to explore the new and exotic properties that topological insulators exhibit owing to their unique phase of quantum matter. 11,14 These electronic states are metallic and robust to the time reversal invariant perturbations like non-magnetic impurities, defects and vacancies in the sample and have been experimentally probed by various experimental techniques, such as angle resolved photoemission spectroscopy (ARPES), scanning tunnelling microscopy (STM) and quantum interference experiments at low temperatures. 8 This is a hallmark for a topological insulator, which is characterised by an odd number of Dirac cones at the Fermi surface, as opposed to an analogous material, Graphene, which has an even number of Dirac cones. 13 These electronic surface states exhibit a relativistic energy – momentum dispersion relation, constituting a single Dirac cone at the Fermi surface. 9–12 Ideally topological insulators have insulating bulk band gap and spin polarized conducting electronic surface states (or edge states in two- dimension) arising out of strong spin orbit interaction. 1–3 These class of materials were predicted theoretically 4–8 and subsequently experimentally realized a few years ago in HgTe quantum wells which is a 2D TI and bismuth based materials Bi 2Se 3, Bi 2Te 3 and Sb 2Te 3 which are 3D TI by separate groups. The extremely large magnetoresistance and high mobility of topological insulators have great technological value and can be exploited in magnetoelectric sensors and memory devices.Topological insulators (TI) are a new state of quantum matter characterized by spin momentum locked gapless surface states which are protected by time reversal symmetry. At high charge-carrier concentrations, there is a greater number of conduction channels and a decrease in the phase coherence length compared to low charge-carrier concentrations. The physical parameters characterizing the WAL effects are calculated using the Hikami-Larkin-Nagaoka formula. The observations of an extremely large nonsaturating magnetoresistance and ultrahigh mobility in the samples with lower carrier density further support the presence of surface states. ![]() WAL due to topological surface states shows no dependence on the nature (electrons or holes) of the bulk charge carriers. At high charge-carrier density the WAL curves scale with neither the applied field nor its normal component, implying a mixture of bulk and surface conduction. At low charge-carrier density the WAL curves scale with the normal component of the magnetic field, demonstrating the dominance of topological surface states in magnetoconductivity. Weak antilocalization (WAL) effects in Bi 2 Te 3 single crystals have been investigated at high and low bulk charge-carrier concentrations. ![]()
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