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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.


(a, b) Single-crystal XRD patterns of TlBiSe2 and TlBiS2 taken on the c-plane. Arrows show peaks at (0 0 9). (c) Profiles of TlBi(SSex)2 around the (0 0 9) peak normalized by the intensity of (0 0 6) peaks. The normalized intensity shows a clear decrease with decreasing x.
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Figure 4: (a, b) Single-crystal XRD patterns of TlBiSe2 and TlBiS2 taken on the c-plane. Arrows show peaks at (0 0 9). (c) Profiles of TlBi(SSex)2 around the (0 0 9) peak normalized by the intensity of (0 0 6) peaks. The normalized intensity shows a clear decrease with decreasing x.

Mentions: Figures 4(a) and (b) show the single-crystal x-ray profile of TlBiSe2 and TlBiS2. Apparently the intensity of peaks with integer n is much weaker in TlBiS2. Figure 4(c) shows (0 0 9) peaks normalized by those of (0 0 6) for various compositions of TlBi(SSex)2. The intensity decreases with a change in the composition from TlBiSe2 to TlBiS2. As described above, the crystal structure of a series of the Tl-based ternary compound can be understood as an fcc structure distorted along the (111) direction [17, 29]. However, the displacement of chalcogen sites from the fcc position and the alternate order of Tl and Bi causes longer periodicity and produces (0 0 +3) peaks in the XRD profile. Therefore, the smaller intensity of (0 0 6n+3) peaks suggests that the displacement of chalcogens in TlBiS2 is smaller than that in TlBiSe2. In the calculation by Lin et al, the displacement of chalcogens is a key for producing band inversion [17]; this may be an origin of the absence of band inversion in TlBiS2, along with weakness of the spin-orbit interaction due to the lighter element, S.


Synthesis and characterization of 3D topological insulators: a case TlBi(S 1 − x Se x ) 2
(a, b) Single-crystal XRD patterns of TlBiSe2 and TlBiS2 taken on the c-plane. Arrows show peaks at (0 0 9). (c) Profiles of TlBi(SSex)2 around the (0 0 9) peak normalized by the intensity of (0 0 6) peaks. The normalized intensity shows a clear decrease with decreasing x.
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Figure 4: (a, b) Single-crystal XRD patterns of TlBiSe2 and TlBiS2 taken on the c-plane. Arrows show peaks at (0 0 9). (c) Profiles of TlBi(SSex)2 around the (0 0 9) peak normalized by the intensity of (0 0 6) peaks. The normalized intensity shows a clear decrease with decreasing x.
Mentions: Figures 4(a) and (b) show the single-crystal x-ray profile of TlBiSe2 and TlBiS2. Apparently the intensity of peaks with integer n is much weaker in TlBiS2. Figure 4(c) shows (0 0 9) peaks normalized by those of (0 0 6) for various compositions of TlBi(SSex)2. The intensity decreases with a change in the composition from TlBiSe2 to TlBiS2. As described above, the crystal structure of a series of the Tl-based ternary compound can be understood as an fcc structure distorted along the (111) direction [17, 29]. However, the displacement of chalcogen sites from the fcc position and the alternate order of Tl and Bi causes longer periodicity and produces (0 0 +3) peaks in the XRD profile. Therefore, the smaller intensity of (0 0 6n+3) peaks suggests that the displacement of chalcogens in TlBiS2 is smaller than that in TlBiSe2. In the calculation by Lin et al, the displacement of chalcogens is a key for producing band inversion [17]; this may be an origin of the absence of band inversion in TlBiS2, along with weakness of the spin-orbit interaction due to the lighter element, S.

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.