Single-Dirac-Cone Topological Surface States in theTlBiSe2Class of Topological Semiconductors

Abstract

We have investigated several strong spin-orbit coupling ternary chalcogenides related to the (Pb,Sn)Te series of compounds. Our first-principles calculations predict the low temperature rhombohedral ordered phase in TlBiTe2, TlBiSe2, and TlSbX2 (X=Te, Se, S) to be topologically Z2 = -1 nontrivial. We identify the specific surface termination that realizes the single Dirac cone through first-principles surface state computations. This termination minimizes effects of dangling bonds making it favorable for photoemission (ARPES) experiments. Our analysis predicts that thin films of these materials would harbor novel 2D quantum spin Hall states, and support odd-parity topological superconductivity. For a related work also see arXiv:1003.2615v1. Experimental ARPES results will be published elsewhere. PACS numbers:Topological insulators are a recently discovered new phase of quantum matter [1][2][3]. The search for topological insulators in real materials has benefitted from the fruitful interplay between topological band theory of Kane and Mele (2005) and realistic band structure calculations [4][5][6][7][8][9][10][11][12]. As a result, Bi x Sb 1−x , Bi 2 Se 3 and Bi 2 Te 3 have been experimentally realized as three-dimensional topological insulators [6-9, 11, 12]. Recently, this search has been extended to ternary compounds [13,14]. Here, we report first-principles band calculations of Tl-based III-V-VI 2 ternary chalcogenide series, and compare the results to those of the related (Pb,Sn)Te series studied previously in connection with Dirac fermion physics in the 1980s [15]. The low temperature rhombohedral ordered phase in TlBiTe 2 , TlBiSe 2 , and TlSbX 2 (X=Te, Se, S) is predicted to be topologically nontrivial. Moreover, we have carried out first-principles slab computations in order to identify the specific surface termination which gives rise to the simple Dirac-cone surface band for ARPES measurements. An analysis of the symmetry of states indicates that thin films of the present materials would support 2D-quantum spin Hall states.Designing new topological insulators involves modifying atomic structure or doping to shift band orders out of the natural sequence. Consider, for example, the wellknown case of (Pb,Sn)Te with rocksalt structure. The end phase PbTe with face-centered cubic (FCC) lattice is topologically trivial. In contrast, SnTe has band inversions at four equivalent L-points where parities of conduction and valence bands are switched (Fig. 2E). Since this inversion occurs at an even number of points in the Brillouin zone, SnTe is also a topologically trivial band insulator. Fu and Kane [5] proposed that a rhombohedral distortion along a particular 111 direction can induce (Pb,Sn)Te into a strong topological phase because then the band inversion occurs only at the L-point along the 111 direction which is distinguished from the other three L-points (Fig. 1B).The Tl-based III-V-VI 2 ternary chalcogenides M M ′ X 2 are, or can be, approximately viewed as a rhombohedral structure with space group R3m[...

Ab initioelectronic structure of thallium-based topological insulators

“…However, we can compare u with experimental data 36 for the tellurides and find a systematically smaller theoretical u by 1.4%. Also, in a recent calculation, 19 a value of z Te = 0.21Å, which corresponds to u = 0.241, was found for TlSbTe 2 , that is, slightly smaller than the experimental value of u = 0.243. In this publication and a recent work, 21 the importance of optimization of the u parameter for the bulk band structure and topological properties was realized.…”

Termination-dependent topological surface states of the natural superlattice phase Bi4Se3

“…1(c)]. The terraces with different terminations are clearly visible, ranging in size from a few μm 2 to ∼(100 μm) 2 . The fine features in the topography measured in STM clearly reveal two types of surfaces [Figs.…”

“…We find that both terminations exhibit TSS, but with substantially different Kramers point energies and dispersions. We show that many features of the surface band structure can be derived from the idealized case of weakly coupled Bi 2 Crystals of Bi 4 Se 3 were grown by slow cooling a Bi-rich melt. The crystal structure and quality were confirmed by x-ray diffraction.…”

“…Three-dimensional topological insulators (3D TIs) are a new class of materials that exhibit topologically protected helical metallic topological surface states (TSS) and a bulk band gap. [1][2][3][4][5][6][7][8][9][10][11][12] The great interest in 3D TIs is partly due to the fact that they necessarily host exotic bound states at their boundaries when interfaced with other nontopological or topological materials. 13 In addition, several theoretical studies have predicted that novel properties may emerge when topological insulators are interlaced with other materials in a regular superlattice.…”

Observation of a highly spin-polarized topological surface state in GeBi2Te4

“…5,6 A number of materials that hold spin-polarized TSSs have been intensively studied, such as Bi 1−x Sb x , 7,8 Bi 2 Se 3 , 9-12 Bi 2 Te 3 , 13,14 and thallium-and lead-based ternary compounds. [15][16][17][18][19][20][21][22][23] Among these materials, Bi 2 Se 3 has been regarded as the most promising three-dimensional (3D) TI because it possesses a single TSS in a rather wide bulk energy gap. 9,10 However, no surface-isolated conduction has been observed for this binary compound even with the low carrier density realized by the hole doping.…”