Search Results (3)

The exploration initiated by the discovery of the topological insulator (Bi_xSb_1−x)₂Te₃ has extended to unlock the potential of quantum anomalous Hall effects (QAHEs), marking a revolutionary era for topological quantum devices, low-power electronics, and spintronic applications. In this study, we present the epitaxial growth of Cr-doped (Bi_0.4Sb_0.6)₂Te₃ (Cr:BST) thin films via molecular beam epitaxy, incorporating various Cr doping concentrations with varying Cr/Sb ratios (0.025, 0.05, 0.075, and 0.1). High-quality crystalline of the Cr:BST thin films deposited on a c-plane sapphire substrate has been rigorously confirmed through reflection high-energy electron diffraction (RHEED), X-ray diffraction (XRD), and high-resolution transmission electron microscopy (HRTEM) analyses. The existence of a Cr dopant has been identified with a reduction in the lattice parameter of BST from 30.53 ± 0.05 to 30.06 ± 0.04 Å confirmed by X-ray diffraction, and the valence state of Cr verified by X-ray photoemission (XPS) at binding energies of ~573.1 and ~583.5 eV. Additionally, the influence of Cr doping on lattice vibration was qualitatively examined by Raman spectroscopy, revealing a blue shift in peaks with increased Cr concentration. Surface characteristics, crucial for the functionality of topological insulators, were explored via Atomic Force Microscopy (AFM), illustrating a sevenfold reduction in surface roughness as the Cr concentration increased from 0 to 0.1. The ferromagnetic properties of Cr:BST were examined by a superconducting quantum interference device (SQUID) with a magnetic field applied in out-of-plane and in-plane directions. The Cr:BST samples exhibited a Curie temperature (T_c) above 50 K, accompanied by increased magnetization and coercivity with increasing Cr doping levels. The introduction of the Cr dopant induces a transition from n-type ((Bi_0.4Sb_0.6)₂Te₃) to p-type (Cr:(Bi_0.4Sb_0.6)₂Te₃) carriers, demonstrating a remarkable suppression of carrier density up to one order of magnitude, concurrently enhancing carrier mobility up to a factor of 5. This pivotal outcome is poised to significantly influence the development of QAHE studies and spintronic applications. Full article

Materials with strong spin-orbit interaction and superconductivity are candidates for topological superconductors that may host Majorana fermions (MFs) at the edges/surfaces/vortex cores. Bulk-superconducting carrier-doped topological crystalline insulator, indium-doped tin telluride (In-SnTe) is one of the promising materials. Robust superconductivity of In-SnTe nanostructures has been demonstrated recently. Intriguingly, not only 3-dimensional (3D) nanostructures but also ultra-thin quasi-2D and quasi-1D systems can be grown by the vapor transport method. In particular, nanostructures with a controlled dimension will give us a chance to understand the dimensionality and the quantum confinement effects on the superconductivity of the In-SnTe and may help us work on braiding MFs in various dimensional systems for future topological quantum computation technology. With this in mind, we employed gold nanoparticles (GNPs) with well-identified sizes to tailor In-SnTe nanostructures grown by vapor transport. However, we could not see clear evidence that the presence of the GNPs is necessary or sufficient to control the size of the nanostructures. Nevertheless, it should be noted that a weak correlation between the diameter of GNPs and the dimensions of the smallest nanostructures has been found so far. To our surprise, the ones grown under the vapor–liquid–solid mechanism, with the use of the GNPs, contained gold that is widely and inhomogeneously distributed over the whole body. Full article

Topological crystalline insulators (TCIs) have been of great interest in the area of condensed matter physics. We investigated the effect of indium substitution on the crystal structure and transport properties in the TCI system (Pb_1−xSn_x)_1−yIn_yTe. For samples with a tin concentration $x\le 50\%$ , the low-temperature resisitivities show a dramatic variation as a function of indium concentration: with up to ∼2% indium doping, the samples show weak-metallic behavior similar to their parent compounds; with ∼6% indium doping, samples have true bulk-insulating resistivity and present evidence for nontrivial topological surface states; with higher indium doping levels, superconductivity was observed, with a transition temperature, $T_c$ , positively correlated to the indium concentration and reaching as high as 4.7 K. We address this issue from the view of bulk electronic structure modified by the indium-induced impurity level that pins the Fermi level. The current work summarizes the indium substitution effect on (Pb,Sn)Te, and discusses the topological and superconducting aspects, which can be provide guidance for future studies on this and related systems. Full article