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Synthesis and characterization of 3D topological insulators: a case TlBi(S 1 − x Se x ) 2

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ABSTRACT

In this article, practical methods for synthesizing Tl-based ternary III-V-VI2 chalcogenide TlBi(SSex)2 are described in detail, along with characterization by x-ray diffraction and charge transport properties. The TlBi(SSex)2 system is interesting because it shows a topological phase transition, where a topologically nontrivial phase changes to a trivial phase without changing the crystal structure qualitatively. In addition, Dirac semimetals whose bulk band structure shows a Dirac-like dispersion are considered to exist near the topological phase transition. The technique shown here is also generally applicable for other chalcogenide topological insulators, and will be useful for studying topological insulators and related materials.

No MeSH data available.


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Transport properties of TlBiSe2 samples. Samples A, B, and C are grown at a temperature sweep rate of 0.5, 1, and 2 °C/h, respectively. Panels (a)–(c) present the temperature dependences of (a) , (b) RH, and (c) .
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Figure 6: Transport properties of TlBiSe2 samples. Samples A, B, and C are grown at a temperature sweep rate of 0.5, 1, and 2 °C/h, respectively. Panels (a)–(c) present the temperature dependences of (a) , (b) RH, and (c) .

Mentions: Figures 6(a)–(c) show the temperature dependences of (a) resistivity, (b) the Hall coefficient, and (c) Hall mobility for three samples of TlBiSe2 single crystals grown in different conditions. Samples A, B, and C are grown at a temperature sweep rate of 0.5, 1, and 2 °C/h, respectively. The temperature dependences of the resistivity of all the three samples show a metallic behavior (figure 6(a)), and this indicates that the samples are degenerate semiconductors. Figure 6(b) shows that the temperature dependences of the Hall coefficient are not strong, and 4.2–6.2·1019 cm−3 of n-type carriers are doped in this system (the Hall resistivity, , shows a linear B-dependence up to ±7 T). The growth-rate dependences of the transport properties are not simple; figure 6(a) shows that the resistivity of sample A grown by the slowest rate shows the highest resistivity of the three, but the fast-grown sample C does not show the lowest resistivity. The Hall coefficient also depends on the growth conditions, and there is a tendency for the absolute value of the Hall coefficient to decrease with increasing resistivity. This suggests that higher resistivity is not caused by a reduction in the charge carriers, but by an increase in disorder. Indeed, the sample A (B) of highest (lowest) resistivity shows the lowest (highest) Hall mobility (figure 6(c)). Apparently sample B is the best among the three samples, because it has lowest carrier concentration and disorder. On the other hand, I applied the growth conditions of sample C (the temperature sweep rate of 2 °C/h) to other TlBi(SSex)2 systems. The quality of sample C is certainly not the best among the three, but it is reasonably good because the mobility is more than three times of that of sample A. The data for lowest-mobility sample A are consistent with that by Mitsas et al [31], and thus in the present experiment the quality of samples is apparently improved. This is probably because of both the higher purity of the raw materials and the optimization of the growth conditions.


Synthesis and characterization of 3D topological insulators: a case TlBi(S 1 − x Se x ) 2
Transport properties of TlBiSe2 samples. Samples A, B, and C are grown at a temperature sweep rate of 0.5, 1, and 2 °C/h, respectively. Panels (a)–(c) present the temperature dependences of (a) , (b) RH, and (c) .
© Copyright Policy - open-access
Related In: Results  -  Collection

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Show All Figures
getmorefigures.php?uid=PMC5036500&req=5

Figure 6: Transport properties of TlBiSe2 samples. Samples A, B, and C are grown at a temperature sweep rate of 0.5, 1, and 2 °C/h, respectively. Panels (a)–(c) present the temperature dependences of (a) , (b) RH, and (c) .
Mentions: Figures 6(a)–(c) show the temperature dependences of (a) resistivity, (b) the Hall coefficient, and (c) Hall mobility for three samples of TlBiSe2 single crystals grown in different conditions. Samples A, B, and C are grown at a temperature sweep rate of 0.5, 1, and 2 °C/h, respectively. The temperature dependences of the resistivity of all the three samples show a metallic behavior (figure 6(a)), and this indicates that the samples are degenerate semiconductors. Figure 6(b) shows that the temperature dependences of the Hall coefficient are not strong, and 4.2–6.2·1019 cm−3 of n-type carriers are doped in this system (the Hall resistivity, , shows a linear B-dependence up to ±7 T). The growth-rate dependences of the transport properties are not simple; figure 6(a) shows that the resistivity of sample A grown by the slowest rate shows the highest resistivity of the three, but the fast-grown sample C does not show the lowest resistivity. The Hall coefficient also depends on the growth conditions, and there is a tendency for the absolute value of the Hall coefficient to decrease with increasing resistivity. This suggests that higher resistivity is not caused by a reduction in the charge carriers, but by an increase in disorder. Indeed, the sample A (B) of highest (lowest) resistivity shows the lowest (highest) Hall mobility (figure 6(c)). Apparently sample B is the best among the three samples, because it has lowest carrier concentration and disorder. On the other hand, I applied the growth conditions of sample C (the temperature sweep rate of 2 °C/h) to other TlBi(SSex)2 systems. The quality of sample C is certainly not the best among the three, but it is reasonably good because the mobility is more than three times of that of sample A. The data for lowest-mobility sample A are consistent with that by Mitsas et al [31], and thus in the present experiment the quality of samples is apparently improved. This is probably because of both the higher purity of the raw materials and the optimization of the growth conditions.

View Article: PubMed Central - PubMed

ABSTRACT

In this article, practical methods for synthesizing Tl-based ternary III-V-VI2 chalcogenide TlBi(SSex)2 are described in detail, along with characterization by x-ray diffraction and charge transport properties. The TlBi(SSex)2 system is interesting because it shows a topological phase transition, where a topologically nontrivial phase changes to a trivial phase without changing the crystal structure qualitatively. In addition, Dirac semimetals whose bulk band structure shows a Dirac-like dispersion are considered to exist near the topological phase transition. The technique shown here is also generally applicable for other chalcogenide topological insulators, and will be useful for studying topological insulators and related materials.

No MeSH data available.


Related in: MedlinePlus