Topological phase diagram and saddle point singularity in a tunable topological crystalline insulator

Abstract

We report the evolution of the surface electronic structure and surface material properties of a topological crystalline insulator (TCI) Pb1−xSnxSe as a function of various material parameters including composition x, temperature T and crystal structure. Our spectroscopic data demonstrate the electronic groundstate condition for the saddle point singularity, the tunability of surface chemical potential, and the surface states' response to circularly polarized light. Our results show that each material parameter can tune the system between trivial and topological phase in a distinct way unlike as seen in Bi2Se3 and related compounds, leading to a rich and unique topological phase diagram. Our systematic studies of the TCI Pb1−xSnxSe are valuable materials guide to realize new topological phenomena.

Highly Tunable Berry Phase and Ambipolar Field Effect in Topological Crystalline Insulator Pb1–xSnxSe

“…18 Therefore, in the Pb 1−x Sn x Se system two distinct topological phase transitions will occur as the Sn composition x increases. 5 The first one is attributed to the shrink of the lattice constant and the system transforms from trivial to nontrivial states, whereas the second one is a consequence of crystal structure transition, thereby destroying the mirror symmetry and driving the system back to trivial states. 5 Owing to the large gap of SnSe, the Pb 1−x Sn x Se system is believed to be a better platform to study the electric transport behavior of TCI particularly in view of minimizing bulk conduction.…”

“…5 The first one is attributed to the shrink of the lattice constant and the system transforms from trivial to nontrivial states, whereas the second one is a consequence of crystal structure transition, thereby destroying the mirror symmetry and driving the system back to trivial states. 5 Owing to the large gap of SnSe, the Pb 1−x Sn x Se system is believed to be a better platform to study the electric transport behavior of TCI particularly in view of minimizing bulk conduction. In order to explore the intriguing properties of TCI, it is indispensable to realize the ambipolar field effect and achieve the surface dominant conduction, which have not been accessible so far.…”

“…We specially restrict the Sn concentration to be less than x = 0.45 to avoid the structural phase transition. 5 Figure 1a shows the in situ reflection high energy electron diffraction (RHEED) oscillations during the film growth and the inset is a typical RHEED pattern from 16 nm Pb 1−x Sn x Se thin film. A growth rate of 65s/layer enables a good control of film thickness.…”

Magnetooptical determination of a topological index

“…Moreover, the topological phase transition (Fig. 1a) from trivial to non-trivial 5,[28][29][30][31][32][33][34] has also been extensively investigated for both TIs and TCI. However, no direct measurement of a topological index in three-dimensional (3D) condensed matter systems has yet been reported.…”

High-temperature thermoelectric properties of the β-As2−xBixTe3 solid solution

“…Continuously varying the As/Bi ratio could act as a tuning parameter of the spin-orbit coupling that would give rise to a transition from a trivial band insulator to a topological insulator, as observed, for instance, in the Pb 1−x Sn x Se or TlBiSe 2−x S x systems. [16][17][18][19] On a more practical point of view, alloying with Bi may help to increase the power factor of β-As 2 Te 3 and to push the maximum ZT values of β-As 2 Te 3 closer to room temperature.…”