Electronic and spin structure of a family of Sn-based ternary topological insulators

Abstract

We report the bulk and surface electronic properties and spin polarization of a rich family of Sn-based ternary topological insulators studied by means of first-principles calculations within the framework of density functional theory. These compounds exist with the following stoichiometries: SnX 2 Te 4 , SnX 4 Te 7 , and SnBi 6 Te 10 (X = Sb and Bi). Where a septuple layer or a quintuple layer and septuple layer blocks alternate along the hexagonal axis. We reveal that the bulk band gap in these compounds is about 100 meV and recognize a strong dependence of the spin polarization on the cleavage surface. The calculated spin polarization reaches 85% in some cases, that is one of the highest predicted values hitherto. Since the electron spin polarization is a relevant parameter for spintronics technology, this new family is suitable for applications within this field.

Surface electronic structure of the wide band gap topological insulator PbBi4Te4Se3

“…According to our DFT calculations [see Fig. 1(b)] and previous theoretical and experimental results for other systems (PbBi 4 Te 7 [9,19], Sn(Bi, Sb) 4 Te 7 [17], PbBi 4 Te 4 S 3 [22]), the "inner" state DC1, lying closer to the Fermi level, is associated with TSS originated from the 7L-terminated surface, while another "outer" state DC2 can be regarded as TSS induced by the 5L-terminated surface. As for the photoemission intensity, DC1 is less pronounced at low photon energies.…”

“…The calculated band gap is of 270 meV [ Fig. 1(b)], which is notably larger than those computed for SbBi 4 Te 7 (75-100 meV) [17,18] and PbBi 4 Te 7 (100 meV) [19]. The edges of the band gap are formed along the¯ -M direction and, according to the well-known problem of the underestimation of the band gap width obtained in terms of DFT, the many-body correction calculations using, for example, the GW approximation can overcome this issue and bring the theoretical band gap value closer to the experimental one [31].…”

“…Due to unique properties, TSSs are of great interest for the observation of many novel quantum phenomena, in particular, quantum spin Hall effect and quantum anomalous Hall effect [3]. So far, a wide variety of compounds hosting spin-polarized TSSs have been thoroughly studied [4][5][6][7][8][9][10][11][12][13][14][15][16][17][18][19][20][21][22]. After the discovery of narrow-gap tetradymite-type semiconductors with quintuple-layer (QL) crystal structure [4][5][6], further efforts at controlling the electronic structure of TIs and TSSs led to fabrication and study of septuple-layer (SL) compounds [7][8][9].…”

“…Recently, a series of the heterostructures [PbBi 4 Te 7 , PbBi 6 Te 10 , Sn(Bi, Sb) 4 Te 7 ] formed by alternating QL (X 2 Te 3 ) and SL (YX 2 Te 4 ) (X = Bi, Sb; Y = Pb, Sn) blocks of TIs have been theoretically proposed [9,10,[16][17][18] and experimentally verified [9,19,20]. In such a case, terraces with nonequivalent 5L-and 7L-surface terminations are possible after crystal cleavage.…”

Interplay of Topological States on TI/TCI Interfaces

“…For the second ingredient of TCI/TI interface, we have chosen SnBi Te TI [ 9 , 46 , 47 ], which has reasonable matching with in-plane lattice parameters of the SnTe(111) film and, even more important, naturally includes SnTe bilayers. SnBi Te is composed of hexagonally ordered SL blocks stacked along the c axis and separated by van der Waals spacings ( Figure 1 a, right panel).…”