Single Dirac Cone Topological Surface State and Unusual Thermoelectric Property of Compounds from a New Topological Insulator Family

Abstract

Angle resolved photoemission spectroscopy study on TlBiTe2 and TlBiSe2 from a thallium-based ternary chalcogenides family revealed a single surface Dirac cone at the center of the Brillouin zone for both compounds. For TlBiSe2, the large bulk gap (∼200 meV) makes it a topological insulator with better mechanical properties than the previous binary 3D topological insualtor family. For TlBiTe2, the observed negative bulk gap indicates it as a semimetal, instead of a narrow-gap semiconductor as conventionally believed; this semimetality naturally explains its mysteriously small thermoelectric figure of merit comparing to other compounds in the family. Finally, the unique band structures of TlBiTe2 also suggest it as a candidate for topological superconductors.

Discovery of a single topological Dirac fermion in the strong inversion asymmetric compound BiTeCl

“…On the contrary, in an IATI, a uniform magnetic field (or ferromagnetic order) will be sufficient to induce the TME effects (Fig. 1c,e) 6), which is inversion asymmetric owing to its zinc blende structure. However, the inversion asymmetry in HgTe is weak in the sense that the crystal shows no net charge polarization (as we will discuss later).…”

“…However, the inversion asymmetry in HgTe is weak in the sense that the crystal shows no net charge polarization (as we will discuss later). In addition, the small bulk bandgap (∼20 meV) of HgTe induced by strain 6 severely limits the temperature under which new topological phenomena can be observed.…”

“…All of the topological insulators discovered so far in experiment are inversion symmetric [1][2][3][4][5] -except for strained HgTe, which has weak inversion asymmetry, a small bulk gap but no bulk charge polarization 6 . Strong inversion asymmetry in topological insulators would not only lead to many interesting phenomena, such as crystalline-surface-dependent topological electronic states, pyroelectricity and intrinsic topological p-n junctions, but would also serve as an ideal platform for the realization of topological magneto-electric effects 7,8 , which result from the modification of Maxwell equations in topological insulators.…”

Organic topological insulators in organometallic lattices

“…The first one is two-dimensional (2D) TI (quantum spin Hall system) in an HgTe-based quantum well 5,6 . Subsequently, several binary (Bi 2 Te 3 , Bi 2 Se 3 and Sb 2 Te 3 ) [7][8][9][10] , ternary (TlBiTe 2 , TlBiSe 2 and PbBi 2 Te 4 ) [11][12][13] and Heusler compounds [14][15][16] have been found to be three-dimensional (3D) TIs. Most recently, the Bi bilayer [17][18][19][20][21] and actinide-based binary compounds 22 have been predicted to be new families of 2D and 3D TIs, respectively.…”

Layered Cobaltites and Natural Chalcogenides for Thermoelectrics

“…On the other hand, ternary chalcogenides serve as an ideal platform for investigating intricate physical and chemical characteristics controlling the efficiency of thermoelectric materials, and also are promising materials for potential applications in photovoltaics, luminescence, as well as thermoelectric and spintronic devices [10][11][12][13]. Ternary chalcopyrite-structured chalcogenides, such as CuFeS 2 , have attracted particular attention owing to their unique optical, electrical, magnetic, and thermal properties [14][15][16][17][18][19][20][21][22][23][24][25][26][27][28].…”