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Crystal Growth and Magneto-transport of Bi2Se3 Single Crystals

  • Geet Awana
  • Rabia Sultana
  • P. K. Maheshwari
  • Reena Goyal
  • Bhasker Gahtori
  • Anurag Gupta
  • V. P. S. Awana
Letter

Abstract

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 (ρT) 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.

Keywords

Topological insulators Crystal growth Structural details Magneto-resistance 

1 Introduction

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 [8] 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

Panels a and b of Fig. 1 represent the X-ray diffraction patterns of the synthesized single-crystal Bi 2Se 3 sample. The on-surface XRD pattern of the single-crystal Bi 2Se 3 clearly shows the 00l alignment (see Fig. 1a). The Rietveld refinement was carried out on powdered crystal using the FullProf suite toolbar, and the results are shown in Fig. 1b. The synthesized Bi 2Se 3 sample exhibits a rhombohedral crystal structure with a R3m (D5) space group. The lattice parameters as obtained from the Rietveld refinement are a = 4.14 (2), b = 4.14 (2), and c = 28.7010 (7) Å, and the values of α, β, and γ are 90°, 90°, and 120°.
Fig. 1

a X-ray diffraction pattern of the Bi 2Se 3 single crystal, b Rietveld fitted room temperature X-ray diffraction pattern for the powder Bi 2Se 3 crystal

Figure 2(a) represents the SEM image of the Bi 2Se 3 single crystal. The morphology of the synthesized Bi 2Se 3 single crystal exhibits a layered structure, similar to that reported by some of us recently for Bi 2Te 3 single crystals [8]. The left inset of Fig. 2(b) shows the compositional constituents of the studied Bi 2Se 3 single crystal. Only Bi and Se are seen, thus confirming the purity of the synthesized crystal. Further, this implies that the crystal is not contaminated by any abundant impurities like carbon or oxygen. The right inset of Fig. 2(c) depicts the quantitative weight% values of the atomic constituents (Bi and Se). The determined quantitative amounts of Bi and Se in the studied Bi 2Se 3 crystal were found to be very near to stoichiometric, i.e., close to Bi 2Se 3.
Fig. 2

(a) Scanning Electron Microscopy image of Bi 2Se 3 Single Crystal, (b) and (c) shows elemental analysis of Bi 2Se 3 Single Crystal

Figure 3 represents the percentage change of magneto-resistance (MR) under applied magnetic fields of up to 14 T at various temperatures ranging from 2 to 200 K. The MR is obtained using the equation MR = [ R(H) − R(0)] / R(0). Figure 3 clearly shows that the synthesized Bi 2Se 3 crystal exhibits linearly increasing MR (%) values, reaching up to 240 % at 2 K under an applied magnetic field of about 14 T. Also, oscillations are seen in MR above say 10 T field at 2 K, which are marked by the arrows. These quantum oscillations can be referred to as the Shubnikov-de Haas (SdH) oscillations. More work is underway to quantify the observed MR oscillations. Clearly, the MR is linear and positive with quantum oscillatory changes at higher magnetic fields (>∼ 10 T). The MR oscillatory behavior is observed at 2 K only, and at higher temperatures of 100 and 200 K, though the MR is yet large enough and linear, the oscillations are not seen. The linear MR and low-temperature oscillatory changes are in agreement with some of the earlier reported literature on topological insulators [9, 11]. The inset of Fig. 3 represents the resistivity versus temperature plots under applied magnetic fields [ ρ(T)H] of 0, 5, and 10 T magnetic fields for the synthesized Bi 2Se 3 single crystal. Clearly, the ρT plots for Bi 2Se 3 with and without the magnetic field are of metallic nature. The resistivity at 200 K under the absence of a magnetic field (0 T) is found to be around 0.52 m Ω-cm, and the same increases to 0.62 and 0.756 m Ω-cm, respectively, under applied magnetic fields of 5 and 10 T. All the ρ(T)H plots show positive temperature coefficients, representing that the synthesized single crystal exhibits a metallic behavior.
Fig. 3

MR (%) as a function of the magnetic field for Bi 2Se 3 at different temperatures; the inset shows the temperature-dependent electrical resistivity of the Bi 2Te 3 single crystal under different applied magnetic fields

Figure 4 represents Kohler’s plot for the synthesized Bi 2Se 3 single crystal. According to Kohler’s rule, the ratio of Δρ/ ρ o and B/ ρ o at different temperatures should consolidate onto a single line in the case of a single type of charge carriers under applied magnetic fields [12]. Here, ρ o is the residual resistivity at 0 K, as being obtained from the extrapolated ρ(T) plot. Interestingly, Kohler’s plot of the magneto-resistance of Bi 2Se 3 consolidates onto a single line. Consequently, we can say that the synthesized Bi 2Se 3 single crystal does obey Kohler’s rule in contrast to previously reported Bi 2Te 3 [8].
Fig. 4

Kohler plot for Bi 2Te 3 in a field range from 0 to 14 T at several temperatures

Figure 5 depicts the Shubnikov-de Haas (SdH) oscillations of the Bi 2Se 3 single crystal at 2 K under different applied magnetic fields ranging from 4 to 14 T. Here, the SdH oscillations plotted as Δρ/ ρ o versus the magnetic field at 2 K are calculated by subtracting the experimentally obtained MR (%) versus the magnetic field from the linear-fitted MR (%). One can observe the SdH oscillations with an increase in the magnetic field from say above 8 T to about 14 T. As mentioned before, more studies are underway to quantify the SdH oscillations.
Fig. 5

Possible Shubnikov-de Haas oscillations of the Bi 2Se 3 single crystal at 2 K

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.

Notes

Acknowledgments

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.

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Copyright information

© Springer Science+Business Media New York 2017

Authors and Affiliations

  • Geet Awana
    • 1
  • Rabia Sultana
    • 2
  • P. K. Maheshwari
    • 2
  • Reena Goyal
    • 2
  • Bhasker Gahtori
    • 2
  • Anurag Gupta
    • 2
  • V. P. S. Awana
    • 2
  1. 1.Department of Physics and AstrophysicsDelhi UniversityNew DelhiIndia
  2. 2.CSIR-National Physical LaboratoryNew DelhiIndia

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