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Milling of 2D flakes is a simple method to fabricate nanomaterial of any desired shape and size. Inherently milling process can introduce the impurity or disorder which might show exotic quantum transport phenomenon when studied at the low temperature. Here we report temperature dependent weak antilocalization (WAL) effects in the sculpted nanowires of topological insulator in the presence of perpendicular magnetic field. The quadratic and linear magnetoconductivity (MC) curves at low temperature indicate the bulk contribution in the transport. A cusp feature in magnetoconductivity curves (positive magnetoresistance) at ultra low temperature and at magnetic field, less than 1T represent the WAL indicating the transport through surface states. The MC curves are discussed by using the 2D Hikami Larkin Nagaoka theory. The crossover interplay nature of positive and negative magnetoresistance observed in the MR curve at ultra low temperature. Our results indicate that transport through topological surface states (TSS) in sculpted nanowires of Bi2Te3 can be achieved at mK range and linear MR observed at 2 K could be the coexistence of electron transport through TSS and contribution from the bulk band., Comment: 8 pages 3 fig

Studies of negative magnetoresistance in novel materials have recently been in the forefront of spintronic research. Here, we report an experimental observation of the temperature dependent negative magnetoresistance in Bi2Te3 topological insulator (TI) nanowires at ultralow temperatures (20 mK). We find a crossover from negative to positive magnetoresistance while increasing temperature under longitudinal magnetic field. We observe a large negative magnetoresistance which reaches -22% at 8T. The interplay between negative and positive magnetoresistance can be understood in terms of the competition between dephasing and spin-orbit scattering time scales. Based on the first-principles calculations within a density functional theory framework, we demonstrate that disorder (substitutional) by Ga+ ion milling process, which is used to fabricate nanowires, induces local magnetic moments in Bi2Te3 crystal that can lead to spin-dependent scattering of surface and bulk electrons. These experimental findings show a significant advance in the nanoscale spintronics applications based on longitudinal magnetoresistance in TIs. Our experimental results of large negative longitudinal magnetoresistance in 3D TIs further indicate that axial anomaly is a universal phenomenon in generic 3D metals., Comment: 14 pages, 4 figures

Proximity induced superconducting energy gap in the surface states of topological insulators has been predicted to host the much wanted Majorana fermions for fault tolerant quantum computation. Recent theoretically proposed architectures for topological quantum computation via Majoranas are based on large networks of Kitaevs one dimensional quantum wires, which pose a huge experimental challenge in terms of scalability of the current single nanowire based devices. Here, we address this problem by realizing robust superconductivity in junctions of fabricated topological insulator Bi2Se3 nanowires proximity coupled to conventional s wave superconducting W electrodes. Milling technique possesses great potential in fabrication of any desired shapes and structures at nanoscale level, and therefore can be effectively utilized to scale up the existing single nanowire based design into nanowire based network architectures. We demonstrate the dominant role of ballistic topological surface states in propagating the long range proximity induced superconducting order with high IcRN product in long Bi2Se3 junctions. Large upper critical magnetic fields exceeding the Chandrasekhar Clogston limit suggests the existence of robust superconducting order with spin triplet cooper pairing. An unconventional inverse dependence of IcRN product on the width of the nanowire junction was also observed., Comment: 12 pages

We report the experimental observation of variable range hopping conduction in focused-ion-beam (FIB) fabricated ultra-narrow nanowires of topological insulator (Bi2Se3). The value of the exponent in the hopping equation was extracted as ~ 1/2 for different widths of nanowires, which is the proof of the presence of Efros-Shklovskii hopping transport mechanism in a strongly disordered system. High localization lengths (0.5nm, 20nm) were calculated for the devices. A careful analysis of the temperature dependent fluctuations present in the magnetoresistance curves, using the standard Universal Conductance Fluctuation theory, indicates the presence of 2D topological surface states. Also, the surface state contribution to the conductance was found very close to one conductance quantum. We believe that our experimental findings shed light on the understanding of quantum transport in disordered topological insulator based nanostructures., Comment: 14pages, 4 figures

Since last few years, research based on topological insulators (TI) is in great interests due to intrinsic exotic fundamental properties and future potential applications such as quantum computers or spintronics. The fabrication of TI nanodevices and study on their transport properties mostly focused on high quality crystalline nanowires or nanoribbons. Here we report robust approach of Bi2Se3 nanowire formation from deposited flakes using ion beam milling method. The fabricated Bi2Se3 nanowire devices have been employed to investigate the robustness of topological surface state (TSS) to gallium ion doping and any deformation in the material due to fabrication tools. We report the quantum oscillations in magnetoresistance curves under the parallel magnetic field. The resistance versus magnetic field curves have been studied and compared with Aharonov-Bohm (AB) interference effects which further demonstrate the transport through TSS. The fabrication route and observed electronic transport properties indicate clear quantum oscillations and can be exploited further in studying the exotic electronic properties associated with TI based nanodevices., Comment: 14 pages, 5 figures, accepted in JPCM

Since the discovery of topological insulators (TI), there are considerable interests in demonstrating metallic surface states, their shielded robust nature to the backscattering and study their properties at nanoscale dimensions by fabricating nanodevices. Here we address an important scientific issue related to TI whether one can clearly demonstrate the robustness of topological surface states (TSS) to the presence of disorder that does not break any fundamental symmetry. The simple straightforward method of FIB milling was used to synthesize nanowires of Bi2Se3 which we believe an interesting route to test robustness of TSS and obtained results are new compared to many of the earlier papers on quantum transport in TI demonstrating robustness of metallic SS to gallium doping. In presence of perpendicular magnetic field, we have observed the co-existence of Shubnikov de Haas oscillations and linear magnetoresistance which was systematically investigated at different channel lengths indicating the Dirac dispersive surface states. The transport properties and estimated physical parameters shown here demonstrate the robustness of SS to the fabrication tools triggering flexibility to explore new exotic quantum phenomena at nanodevice level., Comment: Accepted in JPCM