Giant Rashba Splitting in Pb_1–xSn_xTe (111) Topological Crystalline Insulator Films Controlled by Bi Doping in the Bulk

Abstract

to external perturbations. [10,15,16] Therefore, the trivial to nontrivial topological phase transition can be controlled by many different means, such as by varying temperature, [1,6] pressure, [2] hybridization in ultrathin film geometries, [17][18][19] magnetic interactions, [20] or by breaking of mirror symmetries by strain, [16,[21][22][23] electrostatic fields, [18] or ferroelectric (FE) lattice distortions. [24,25] This provides ample degrees of freedom for topology control not available in conventional Z 2 TIs. For this reason, TCIs offer an ideal template for observation of exotic phenomena such as partially flat band helical snake states and interfacial superconductivity, [16] large-Chern-number quantum anomalous Hall effect, [26] as well as for realization of novel topology-based devices such as topological photodetectors, [23] spin transistors, [18] and spin torque devices. [27] For most of such applications, thin film structures with precisely controlled composition and Fermi level are required. Up to now, most work has been performed on highly p-type bulk crystals exploiting the natural (001) cleavage plane of the IV-VI compounds, [3,4,6] whereas for other surface orientations and practical devices epitaxial TCI film structures are required. [18,[28][29][30][31][32] The (111) orientation is particularly interesting due to the polar nature of its surface [12] as well as the ease of lifting the fourfold valley degeneracy at the L-points of the Brillouin zone (BZ) [33] by opening a gap at particular Dirac points by strain [16] and quantum confinement [17][18][19] to induce a transition from a TCI to a normal Z 2 -TI material. [25]

Ferromagnetic phase transition in topological crystalline insulator thin films: Interplay of anomalous Hall angle and magnetic anisotropy

“…The Sn vacancies and thus the hole concentration in SnTe can be controlled and tuned by adjusting the Te flux during deposition. The desired Mn concentrations have been achieved by regulating the Mn flux calibrated according to well-established growth protocols [40,42]. The actual Mn concentrations have been confirmed via high-resolution x-ray diffraction (HRXRD) measurements.…”

“…In the present study, the growth of the Sn 1−x Mn x Te thin films is carried out in excess of Te flux in order to control the stoichiometry of the crystal. The film thickness is determined on-line with a quartz microbalance [40] and the epitaxial process is monitored by means of in situ reflection high-energy electron diffraction (RHEED). A protocol of surface and structural characterization, including atomic force microscopy (AFM) and HRXRD provides control on the quality of the layers and confirms the absence of Mn-precipitation, ruling out the formation of secondary phases.…”

“…The IV-VI compounds have been widely studied as thermoelectric materials, as photodetectors and as dilute magnetic semiconductors [41][42][43][44][45]. The interest in the topological behavior of undoped and magnetically doped IV-VI compounds, both in the bulk and thin layer arrangement, has significantly increased recently [39,40,[43][44][45][46][48][49][50]. By means of ARPES, it was demonstrated, that the four Dirac cones of the TCIs are spin non-degenerate and helically spin-polarized [9,10,38].…”

Dirac Landau Level Spectroscopy in Pb1−xSnxSe and Pb1−xSnxTe across the Topological Phase Transition: A Review

“…We have reported a thorough quantification of the bulk band gap near the topological phase transition, and have not yet observed a bulk gap closure [17]. Pb 1−x Sn x Te samples having high Sn content are, however, Bi-doped (0.01%-0.2%) [38]. The Bi content is likely to have some impacts on the band gap.…”

“…Electron-electron correlations and electron-phonon coupling were among the possible interactions considered [39][40][41]. More conventionally, alloy disorder and impurity doping were also argued to lead to the gapping of the 3D Dirac state [37,38].…”