Crystal Growth and Magneto-transport of Bi2Se3 Single Crystals
In this letter, we report on the growth and characterization of bulk Bi 2Se 3 single crystals. The studied Bi 2Se 3 crystals are grown by the self-flux method through the solid-state reaction from high-temperature (950 °C) melt of constituent elements and slow cooling (2 ℃/h). The resultant crystals are shiny and grown in the [00l] direction, as evidenced from surface XRD. Detailed Reitveld analysis of powder X-ray diffraction (PXRD) of the crystals showed that these are crystallized in the rhombohedral crystal structure with a space group of R3m (D5), and the lattice parameters are a = 4.14 (2), b = 4.14 (2), and c = 28.7010 (7) Å. Temperature versus resistivity (ρ−T) plots revealed metallic conduction down to 2 K, with typical room temperature resistivity (ρ 300 K) of around 0.53 m Ω-cm and residual resistivity (ρ 0 K) of 0.12 m Ω-cm. Resistivity under magnetic field [ ρ(T)H] measurements exhibited large + ve magneto-resistance right from 2 to 200 K. Isothermal magneto-resistance [ ρH] measurements at 2, 100, and 200 K exhibited magneto-resistance (MR) of up to 240 %, 130 %, and 60 %, respectively, at 14 T. Further, the MR plots are nonsaturating and linear with the field at all temperatures. At 2 K, the MR plots showed clear quantum oscillations at above say 10 T applied field. Also, the Kohler plots, i.e., Δρ/ ρ oversus B/ ρ, were seen consolidating on one plot. Interestingly, the studied Bi 2Se 3 single crystal exhibited the Shubnikov-de Haas (SdH) oscillations at 2 K under different applied magnetic fields ranging from 4 to 14 T.
KeywordsTopological insulators Crystal growth Structural details Magneto-resistance
Topological insulators (TI) are a kind of wonder material of topical interest today, whereby the interior of the material is band insulating and the surface states are conducting [1, 2]. Interestingly, the conducting surface states of the topological insulators are symmetry protected [3, 4, 5]. Further, the surface state carriers are quantized as their spins are locked in right angle to their momentum [1, 2, 3, 4, 5]. This gives rise to time reversal symmetry-driven protected states. Clearly, the role of both the spin and the momentum of the protected surface states is important and hence the topological insulators are often called the futuristic potential spintronic materials [4, 5, 6, 7]. No wonder, topological insulators with their rich physics and potential applications are the hottest topic today for condensed matter physicists including both theoreticians and experimentalists alike [1, 2, 3, 4, 5, 6, 7].
For experimental condensed matter physicists, the work line starts from material, measurement to mechanism, i.e., MMM. Basically, first and foremost, the task is to identify the master material and synthesize the same in the right structure with the best possible purity. The state-of-the-art measurements for various physical properties are the next step. Once the quality material is in place and the physical property characterization is over, one sits back and tries to analyze the results and explore the theoretical explanation and mechanism for the obtained physical property.
Keeping in view the fact that the topological insulators are the real hot cakes presently for condensed matter physicists and, often in the beginning of a new field, the material quality is not always optimized to the best levels, we focus on the growth and physical property characterization of by now one of the popular TI, i.e., Bi 2Se 3. We did grow large (cm size) bulk Bi 2Se 3, exhibiting the metallic character down to 2 K and large + ve linear magneto-resistance of up to 250 % at 2 K under an applied field of 14 T coupled with clear quantum oscillations above say 10 T.
2 Experimental Details
The Bi2Se 3 sample is grown via the self-flux method  in an evacuated sealed quartz tube heating up to a temperature of 950 ℃(2 ℃/min) and then cooling down slowly to 650 °C (2 ℃/h). Both bismuth (Bi) and selenium (Se) powder were accurately weighed according to the stoichiometric ratio of 2:3 and then well mixed with the help of a mortar and pestle. The above steps were performed in the presence of high-purity argon atmosphere within a glove box (MBRAUN Labstar). The obtained mixed powder was then pelletized into a rectangular pellet form under a pressure of 50 kg/cm 2 by means of a hydraulic press. After the pelletization was over, the pellet was then sealed into an evacuated (10 −3 Torr) quartz tube and placed inside the tube furnace. The furnace was heated up to 950 ℃(2 ℃/min) and then cooled very slowly to 650 ℃(2 ℃/h), after which the same was switched off and allowed to cool naturally to room temperature. The structural characterization was performed through room temperature X-ray diffraction (XRD) using Cu-K α radiation (λ = 1.5418 Å). However, the magnetic measurements were done using the quantum design Physical Property Measurement System (PPMS). Also, scanning electron microscopy (SEM) and energy-dispersive X-ray spectroscopy (EDAX) were carried out using ZEISS-EVO MA-10.
3 Results and Discussions
Summarily in current letter, we reported the growth, structure, and brief magneto-transport characterization of self-flux grown Bi 2Se 3 single crystals. The as-grown crystals are large (few cm) in size having a metallic conductivity down to 2 K and high non-saturating + ve magneto-resistance to the tune of above 240 % at 2 K in an applied field of 14 T. The high MR (250 %, 2 K, 14 T) also exhibited the quantum oscillations.
The authors from CSIR-NPL acknowledge the encouragement and support of their director Prof. D. K. Aswal. Geet Awana thanks Prof. Sanjay Jain, Head of the Department of Physics and Astrophysics, Delhi University, for his support.
- 10.Akiyama, R., Sumida, K., Ichinokura, S., Kimura, A., Kokh, KA., Tereshchenko, O.E., Hasegawa, S.: arXiv:1701.00137